Gait & Posture - Articles in Press

The influence of hip abductor muscle performance on dynamic postural stability in females with patellofemoral pain - Corrected Proof

Szu-Ping Lee, Richard B. Souza, Christopher M. Powers — 2012-05-18

Highlights: ► Hip abductor performance is important for maintaining postural stability during unipedal tasks. ► We compared postural stability in females with patellofemoral pain (PFP) to pain-free controls during a step-down task. ► Females with PFP exhibited significant hip abductor weakness and decreased postural stability. ► A hip stabilizing brace helped improving postural stability in females with PFP.Abstract: Hip abductors play an important role in maintaining trunk and pelvis stability during unipedal tasks. The purpose of the study was to compare postural stability between individuals with patellofemoral pain (PFP) and pain-free controls. A secondary purpose was to evaluate the effect of a hip stabilizing brace on postural stability. Twenty females with PFP (27.3±6.3 years) and 19 controls (26.1±4.5 years) participated. Each subject performed a unipedal step-down balance task with the stance leg on a force platform from which center of pressure (COP) excursion was recorded. Quantitative COP excursion patterns (mean and peak displacements) were used as measures of postural stability. For subjects with PFP, postural stability also was quantified following the application of a hip stabilizing brace. Hip abductor strength was significantly lower in PFP group compared to the control group (1.39±0.4 vs. 1.62±0.26N/kg-BW, p=0.046). Peak and mean medial–lateral COP displacements during the balance task were greater in the PFP group (39.8±6.7 vs. 24.3±3.8mm, p<0.001; 24.7±16.3 vs. 13.5±4.4mm, p=0.005). Application of the hip stabilizing brace reduced the peak and mean COP displacement (39.8±6.7 vs. 24.7±4.7mm, p<0.001; 24.7±16.3 vs. 16.8±15.1mm, p=0.02). Our results demonstrate that females with PFP exhibit impaired medial–lateral postural stability when compared to control subjects. Application of a hip stabilizing brace significantly improved stability to a level comparable to the controls.

Foot kinematics and loading of professional athletes in American football-specific tasks - Corrected Proof

2012-05-17

Highlights: ► We measured the foot motion and ground reaction forces of American football specific activities. ► Nine professional level football players, three each from three classes of players participated. ► Activities included initiation of motion, cutting, running, jumping and landing, and planting. ► Foot motion parameters included talocrural, metatarsophalangial joint, and subtalar angles. ► The athlete's foot motion routinely reached the accepted range of motion limits for all joints.Abstract: The purpose of this study was to describe stance foot and ankle kinematics and the associated ground reaction forces at the upper end of human performance in professional football players during commonly performed football-specific tasks. Nine participants were recruited from the spring training squad of a professional football team. In a motion analysis laboratory setting, participants performed three activities used at the NFL Scouting Combine to assess player speed and agility: the 3-cone drill, the shuttle run, and the standing high jump. The talocrural and first metatarsophalangial joint dorsiflexion, subtalar joint inversion, and the ground reaction forces were determined for the load bearing portions of each activity. We documented load-bearing foot and ankle kinematics of elite football players performing competition-simulating activities, and confirmed our hypothesis that the talocrural, subtalar, and metatarsophalangeal joint ranges of motion for the activities studied approached or exceeded reported physiological limits.

Repeatability of a 3D multi-segment foot model protocol in presence of foot deformities - Corrected Proof

2012-05-17

Abstract: Repeatability studies on 3D multi-segment foot models (3DMFMs) have mainly considered healthy participants which contrasts with the widespread application of these models to evaluate foot pathologies. The current study aimed at establishing the repeatability of the 3DMFM described by Leardini et al. in presence of foot deformities.Foot kinematics of eight adult participants were analyzed using a repeated-measures design including two therapists with different levels of experience.The inter-trial variability was higher compared to the kinematics of healthy subjects. Consideration of relative angles resulted in the lowest inter-session variability. The absolute 3D rotations between the Sha-Cal and Cal-Met seem to have the lowest variability in both therapists. A general trend towards higher σsess/σtrial ratios was observed when the midfoot was involved.The current study indicates that not only relative 3D rotations and planar angles can be measured consistently in patients, also a number of absolute parameters can be consistently measured serving as basis for the decision making process.

Gender differences in trunk, pelvis and lower limb kinematics during a single leg squat - Corrected Proof

Valentina Graci, Linda R. Van Dillen, Gretchen B. Salsich — 2012-05-16

Highlights: ► We investigate gender differences in multi-joints movement strategies to complete a squat on a single leg. ► Females flex less their trunk and display greater hip adduction and knee abduction than males. ► Females rotate non weighting trunk and pelvis toward the weight-bearing limb at 45° of knee flexion. ► Males rotate their trunk toward the weight-bearing limb and pelvis toward the nonweight-bearing limb. ► Females show a multi-segmental movement pattern that could expose them to knee injury and pain development.Abstract: The relationship between trunk and lower limb kinematics in healthy females versus males is unclear since trunk kinematics in the frontal and transverse planes have not been systematically examined with lower limb kinematics. The aim of this study was to investigate the existence of different multi-joints movement strategies between genders during a single leg squat. We expected that compared to males, females would have greater trunk and pelvis displacement due to less trunk control and display hip and knee movement consistent with medial-collapse (i.e. greater hip adduction, hip medial rotation, knee abduction, and knee lateral rotation) on the weight-bearing limb.Nine females and 10 males participated in the study. Kinematic data were collected using an 8-camera, 3D-motion-capture-system. Trunk relative to pelvis, pelvis relative to the laboratory, hip and knee angles in three planes (sagittal, frontal and transverse) were examined at two time events relevant to knee joint mechanics: 45° of knee flexion and peak knee flexion.Females flexed their trunk less than males and rotated their trunk and pelvis toward the weight-bearing limb more than males. Females also displayed greater hip adduction and knee abduction than males.Taken together these results suggest that females and males used different movement strategies during a single leg squat. Females displayed a trunk and pelvic movement pattern that may put them at risk of knee injury and pain.

Stair ascent kinematics and kinetics with a powered lower leg system following transtibial amputation - Corrected Proof

Jennifer M. Aldridge, Jordan T. Sturdy, Jason M. Wilken — 2012-05-09

Highlights: ► Eleven individuals with unilateral transtibial amputation were assessed using conventional and powered prostheses. ► We determined if increasing ankle power normalized lower limb kinematics and kinetics during stair ascent. ► The powered device demonstrated greater ankle power generation and plantarflexion during stair ascent. ► Deviations from normal stair ascent gait persisted at the hip and knee despite changes in ankle kinematics and kinetics. ► Additional device specific training may be necessary to utilize the full benefits of a powered device.Abstract: During stair ascent (STA) persons with transtibial amputation (TTA) typically adopt a hip strategy to compensate for the limited ankle motion and joint power that is characteristic of conventional energy storing and returning (ESR) prosthetic feet. The purpose of this investigation was to determine if providing ankle power via a powered prosthetic device (BiOM) normalized STA kinematics and kinetics. Eleven individuals with TTA participated in two STA gait analysis sessions: (1) using an ESR foot, and (2) using the BiOM. Eleven height and weight matched able-bodied controls (CONT) were also assessed. Lower extremity peak kinematic and kinetic values were calculated at a self-selected and controlled cadence (80steps/min). Increased prosthetic limb peak ankle plantarflexion and push-up power were observed while using the BiOM as compared to ESR. Peak ankle power was not significantly different between BiOM and CONT indicating normalization of ankle power generation. However, peak ankle plantarflexion was significantly lower than CONT. Limb asymmetries including greater prosthetic limb hip flexion and power during stance, and decreased prosthetic limb knee power during stance were observed in the BiOM and ESR conditions. The results suggest that the BiOM successfully increased ankle motion and restored ankle power during STA. These differences did not, however, reduce the use of a hip strategy while ascending stairs. Additional device specific training may be necessary to utilize the full benefits of the device.

Dual-tasking interferes with obstacle avoidance reactions in healthy seniors - Corrected Proof

2012-05-07

Highlights: ► Sensitive outcome parameters can reveal subtle dual-task interference. ► Both tasks were attentionally demanding. ► Obstacle avoidance response is slowed during dual-tasking. ► Stroop task performance is decreased during and just after obstacle avoidance.Abstract: Dual-tasking can lead to falls, as does a deterioration of obstacle avoidance (OA) skills. Hence, it is expected that a combination of both would be even more detrimental, especially when OA is time-critical. Previous studies confirmed this expectation, however, due to several limitations in their design it is yet too early to draw any definitive conclusions on the allocation of attentional resources in OA under dual-task conditions. Therefore, attentionally demanding primary and secondary tasks were used with the instruction to perform as well as possible on both tasks. Nineteen healthy senior individuals (60±4.7 years, 8 females) performed an OA task on a treadmill while walking at 3km/h as a single task and combined with an auditory Stroop task. Biceps femoris (BF) muscle response times, OA failure rates and composite scores were used to evaluate the data. Increased OA failure rates (3%, p=0.03) and delayed BF response times (21ms, p<0.001) were found under dual-task conditions. Composite scores were reduced during (p<0.001) and just after obstacle crossing (p=0.003). In conclusion, dual-tasking during time-critical OA affects the motor as well as the cognitive task when subjects are instructed to keep up performance on both tasks. This adds to the evidence indicating an increased risk of tripping or falling when attention is divided during walking in the presence of unexpected obstacles.

A comparison of hip joint centre localisation techniques with 3-DUS for clinical gait analysis in children with cerebral palsy - Corrected Proof

Alana Peters, Richard Baker, M.E. Morris, Morgan Sangeux — 2012-05-07

Highlights: ► A range of regression equations and functional techniques were tested against 3-d ultrasound for determining the hip joint centre location. ► Forty-six children, representing those attending a major clinical gait analysis service were tested. ► Best agreement with ultrasound was for the Harrington equations (mean 14mm, sd 8mm). ► Sphere fitting (mean≈22mm, sd 11mm) performed better than transformational techniques applied locally (mean≈33mm, sd 12mm) or globally (mean=30mm, sd 14mm).Abstract: Functional calibration techniques have been proposed as an alternative to regression equations for estimating the position of the hip within the pelvic co-ordinate system for clinical gait analysis. So far validation of such techniques has focussed on healthy adults. This study evaluated a range of techniques based on regression equations or functional calibration procedures techniques in 46 children representative of those attending a major clinical gait analysis service against previously validated 3-D ultrasound techniques for determining the hip joint centre. Best agreement with ultrasound for the position of the hip within the pelvic coordinate system was found for the Harrington equations (mean 14mm, sd 8mm). Sphere fitting (mean≈22mm, sd 11mm) performed better than transformational techniques applied locally (mean≈33mm, sd 12mm) or globally (mean=30mm, sd 14mm). The participants with cerebral palsy showed reduced range of movement compared with healthy adults. Differences between these results and studies modelling the effects of simulated noise on functional techniques can probably be attributed to differences between that noise and the soft tissue displacements that are actually occurring.

Minimal predicted distance: A common metric for collision avoidance during pairwise interactions between walkers - Corrected Proof

Anne-Hélène Olivier, Antoine Marin, Armel Crétual, Julien Pettré — 2012-05-07

Highlights: ► We experimentally studied collision avoidance between two walkers. ► Walkers were able to accurately predict the risk of a future collision. ► They performed collision avoidance manoeuvres only when required. ► Collision avoidance was solved with anticipation. ► We detail the three phases that compose an avoidance: observation, reaction and regulation.Abstract: This study investigated collision avoidance between two walkers by focusing on the conditions that lead to avoidance manoeuvres in locomotor trajectories. Following the hypothesis of a reciprocal interaction, we suggested a mutual variable as a continuous function of the two walkers’ states, denoted minimum predicted distance (MPD). This function predicts the risk of collision, and its evolution over time captures the motion adaptations performed by the walkers. By groups of two, 30 walkers were assigned locomotion tasks which lead to potential collisions. Results showed that walkers adapted their motions only when required, i.e., when MPD is too low (<1m). We concluded that walkers are able (i) to accurately estimate their reciprocal distance at the time the crossing will occur, and (ii) to mutually adapt this distance. Furthermore, the study of MPD evolution showed three successive phases in the avoidance interaction: observation where MPD(t) is constant, reaction where MPD(t) increases to acceptable values by adapting locomotion and regulation where MPD(t) reaches a plateau and slightly decreases. This final phase demonstrates that collision avoidance is actually performed with anticipation. Future work would consist in inspecting individual motion adaptations and relating them with the variations of MPD.

Testing single and double limb standing balance performance: Comparison of COP path length evaluation between two devices - Corrected Proof

Lars Donath, Ralf Roth, Lukas Zahner, Oliver Faude — 2012-05-07

Highlights: ► The GKS System moderately corresponds to the gold standard. ► The amount of COP path length overestimation of the GKS System decreased with task severity. ► COP path length evaluating systems should be carefully interpreted interchangeably.Abstract: Center of pressure (COP) path length evaluation was commonly applied to measure postural sway and usually obtained from gold standard force plates. Thus, we comparatively investigated the feasible and less-expensive GKS® balance system (GKS) with the Kistler® force platform (KIS).34 non-specifically trained but active adults (14 males, 20 females, age: 25.4±4.8 years; weight: 69.3±12.3kg; height: 1.75±0.09m, sports activity: 5.8±3.6hours per week) were randomly tested on both devices during double and single limb stance with opened and closed eyes.Irrespective of the analysed time frame, repeated measures analyses of variances revealed higher path length readings for GKS compared to KIS for 30s (F=6.8, p=0.01) and 10s (F=21.2, p=0.001). Large effect sizes of the COP path length differences between GKS and KIS decreased from easy tasks (double limb, eyes open; d30-s=2.55, d10-s=2.04) to the most severe task (single limb, eyes closed; d30-s=0.02, d10-s=0.23). According to Bland and Altman, the limits of agreements indicated a high random variability component (between 29%, double limb, eyes open and 67%, single limb, eyes closed). The overall intraclass correlation coefficients (ICC) across all four standing balance tasks were moderate for the 30 s- (0.57) as well as the 10 s-analysis (0.65).In conclusion, the COP path length displacements obtained from the GKS balance system seem to differ with a considerable random variability from Kistler force platform data. Thus, measurements of the evaluated devices should not be used interchangeably. Further methodological investigations regarding balance measures seem warranted.

Biomechanical characteristics of stepping in older Tai Chi practitioners - Corrected Proof

Ge Wu — 2012-05-07

Highlights: ► Compared stepping characteristics of 10 older Tai Chi (TC) and 10 age-matched non-TC individuals. ► Stepping was in the forward and backward directions, with and without mental distractions (MD). ► Both groups had similar step initiation time, step length and forward step width. ► MD delayed step initiation and foot contact time, and shortened step length in both groups. ► TC group had shorter preparation and foot contact time, and wider backward step than non-TC group.Abstract: This study compared the biomechanical characteristics of stepping in 10 older (aged 55+ years) Tai Chi (TC) practitioners and 10 age-matched non-TC (NTC) controls. Subjects were asked to take a step on an auditory cue as fast as possible, in the forward and backward directions, and with and without mental distractions, respectively. Stepping characteristics included step initiation time, preparation time for foot off, foot contact time, and step length and width. The results showed that both groups had similar step initiation time, step length and forward step width (p>0.466). Although mental distraction significantly delayed step initiation time and foot contact time, and shortened step length in both groups (p<0.003), TC practitioners had significantly shorter preparation and foot contact time, and wider backward step width than controls regardless of mental distraction (p<0.024). These group differences are in favor of TC practitioners in situations of postural recovery from potential falls, even with mental distractions, and may explain the positive effect of TC practice on fall reduction in older adults.

Lower limb joints kinematics in essential tremor and the effect of thalamic stimulation - Corrected Proof

2012-05-03

Highlights: ► Thalamic deep brain stimulation modulates the cerebello-thalamo-cortical pathway. ► Joint kinematics of lower limbs are impaired in advanced cases of Essential Tremor. ► Chronic thalamic stimulation normalized this highly variable joints excursion. ► Supratherapeutic thalamic stimulation induces ataxic changes of joint excursion. ► The beneficial effect on ataxic symptoms is limited to a narrow therapeutic window.Abstract: Following the hypothesis that thalamic deep brain stimulation improves ataxia in patients with essential tremor by modulating the cerebello-thalamo-cortical pathway, we examined the joint kinematics of lower limbs during uninterrupted gait in eleven patients who have been treated with bilateral thalamic stimulation for 24.7±20.3 months. Patients were assessed under routine chronic stimulation, supra-therapeutic amplitude, and off stimulation by means of an infrared movement analysis system while walking on a treadmill. Chronic thalamic DBS normalized the highly variable excursion throughout the gait cycle that characterized the subgroup of patients with longest disease duration. Supratherapeutic thalamic DBS amplitude did not reproduce such improvements while, more importantly, it induced ataxic changes of joint excursion. The normalization of kinematic abnormalities argues against the hypothesis of a cerebellar neurodegeneration in ET. Moreover, these results suggest that the beneficial effect of thalamic DBS on ataxic symptoms is limited to a narrow therapeutic window.

The reasons why stroke patients expend so much energy to walk slowly - Corrected Proof

G. Stoquart, C. Detrembleur, T.M. Lejeune — 2012-05-03

Abstract: Background: The energy consumed per covered distance (C) is increased in hemiparetic stroke adults during walking.Objective: To ascertain if increased C in stroke patients is a result of increased mechanical work, of decreased efficiency of work production by muscles or of slow walking speed.Methods: C and mechanical work were computed in 20 patients walking on a force measuring treadmill at speeds ranging from 1kmh−1 to their own maximum speed (WSMAX). Works done by healthy and pathological limbs were computed separately.Results: For hemiparetic patients, C was around 1.7 times greater than normal. When these patients had a slower WSMAX, they had greater C and mechanical work (r=−0.44 and −0.57, respectively). The increased C was related to the external work performed to lift the center of body mass when the healthy limb was supporting the body weight (r=0.77).Conclusions: The increase of C in stroke patients is more pronounced when WSMAX is slow. Moreover, this increase is related to increased mechanical work done by muscles and is not related to slow walking speed or decreased efficiency. As in healthy subjects, C and external work presented optimum speeds, indicating a preserved pendular mechanism of walking.

Integrated assessment techniques for linking kinematics, kinetics and muscle activation to early migration: A pilot study - Corrected Proof

2012-05-03

Highlights: ► It is feasible to integrate fluoroscopic, kinematic and kinetic measurements. ► There seems to be an association between deviant kinematics and early migration. ► The insert and femoral component had comparable axial rotations up to 60° of flexion.Abstract: The goal of this pilot study was to develop and test an integrated method to assess kinematics, kinetics and muscle activation of total knee prostheses during dynamic activities, by integrating fluoroscopic measurements with force plate, electromyography and external motion registration measurements. Subsequently, this multi-instrumental analysis was then used to assess the relationship between kinematics, kinetics and muscle activation and early migration of the tibial component of total knee prostheses. This pilot study showed that it is feasible to integrate fluoroscopic, kinematic and kinetic measurements and relate findings to early migration data. Results showed that there might be an association between deviant kinematics and early migration in patients with a highly congruent mobile-bearing total knee prosthesis. Patients that showed high levels of coactivation, diverging axial rotations of the insert and a deviant pivot point showed increased migration and might be at higher risk for tibial component loosening. In the future, to confirm our findings, the same integrated measurements have to be performed in larger patient groups and different prosthesis designs.

The development, preliminary validation and clinical utility of a shoe model to quantify foot and footwear kinematics in 3-D - Corrected Proof

2012-05-03

Highlights: ► A model to quantify 3-D shoe (foot & footwear) kinematics in clinical situations. ► Preliminary validation through comparison to validated barefoot 3-D models. ► Clinical utility demonstrated with users of Functional Electrical Stimulation (FES).Abstract: Functional electrical stimulation (FES) applied to the common peroneal nerve is commonly prescribed to correct both equinus and excessive foot inversion in swing and initial contact. This paper presents the development of a simple shoe model, to allow quantification of 3-D shoe (foot and footwear) kinematics in clinical situations when footwear is required, e.g. with FES systems requiring footswitches. To preliminarily validate the shoe model, barefoot ‘normal’ adult data (n=11) processed using validated 3-D foot models, were reprocessed with the shoe model. Outputs were compared through calculation of waveform similarity and correlation.Clinical utility of the shoe model is demonstrated through the presentation of 3-D shoe kinematics, calculated from a cohort of existing unilateral common peroneal FES users (n=16), both with and without FES. A trend of reduced inversion at mid-swing and initial contact was seen, although this was not found to be statistically significant (p≤0.0125). The shoe model was found to be practical to use in a clinical environment, and has potential to contribute to the evidence base for interventions such as common peroneal FES.

Reliability of gait parameters during treadmill walking in community-dwelling healthy seniors - Corrected Proof

Oliver Faude, Lars Donath, Ralf Roth, Livia Fricker, Lukas Zahner — 2012-05-03

Highlights: ► We assessed the reliability of gait parameters during treadmill walking in seniors. ► Mostroutine temporal and spatial gait parameters were highly reliable. ► Changes of less than 10% can be detected with 90% confidence in these parameters. ► Gait variability parameters obtained during treadmill walking were less reliable. ► These data may serve as a basis to interpret exercise intervention effects.Abstract: The present study aimed at assessing the between- and within-day-variability of temporal and spatial gait characteristics during treadmill walking in community-dwelling seniors. In 20 active, healthy seniors (10 women, 10 men, age: 64.8 (SD 3.2) years, height: 1.70 (0.10)m, weight: 69.7 (10.9)kg, physical activity: 11 (6)hweek−1) gait characteristics were assessed on three days in weekly intervals (between-day variability). Either on days two or three, testing was repeated 30min after the initial trial (within-day variability). We determined routine spatio-temporal gait parameters as well as gait variability during 400 steps at a normal walking speed (5.0 (0.4)kmh−1) on a one-dimensional ground reaction force measuring treadmill. No significant mean differences occurred in any parameter for between- and within-day comparisons. Between-day ICC were high (ICC≥0.86) for most parameters except for temporal (ICC=0.44) and spatial (ICC=0.22) gait variability. Coefficients of variation (CoV) were also high in the latter parameters (CoV=30.2–36.1%), whereas all other variables showed clearly lower values (CoV<7%). CoV were still lower between days 2 and 3 (CoV<5%). Compared to between-day comparisons, within-day variability was comparable in spatio-temporal gait parameters (CoV<5%, ICC≥0.97) and lower in gait variability parameters (CoV<18%, ICC≥0.72–0.74). In conclusion, most gait parameters were highly reliable during treadmill walking. Changes of less than 10% can be detected with sufficient confidence. Gait variability parameters were less reliable and, thus, should be carefully interpreted.

Adaptive changes of foot pressure in hallux valgus patients - Corrected Proof

Jianmin Wen, Qicheng Ding, Zhiyong Yu, Weidong Sun, Qining Wang, Kunlin Wei — 2012-05-03

Highlights: ► We test plantar foot pressure for 229 Hallux valgus patients, in comparison with healthy controls. ► We systematically control confounding factors in pressure analyses and investigate how pain affects the results. ► We found higher loading in the 1st and 2nd metatarsals and less loading in hallux. ► We found different loading duration and medial-to-lateral load transition. ► All these changes depend on the foot pain.Abstract: Background: Hallux valgus (HV) is one of the most common deformities in podiatric and orthopedic practice. Plantar pressure technology has been widely used in studying the pressure distribution in HV patients for better assessment to plan interventions. However, previous studies produced an array of controversial findings and most of them only focused on the forefoot.Methods: We examined the dynamic changes of foot pressure of the whole foot with a large-sample investigation (229 patients and 35 controls). Foot pain, which has been largely neglected previously, was used to group the participants.Results: Compared to healthy controls, patients had significantly higher loading of the first and second metatarsals, where the transverse arch usually collapses, and significantly less loading of the hallux. Moreover, forces in most regions reached their maximum late, indicating a slow build-up of loading. Patients shortened the loading duration on their forefoot, loaded more on the medial foot starting from early foot contact, and delayed the medial-to-lateral load transition. Notably, nearly all these changes were more pronounced in patients with pain.Conclusions: Biomechanical changes in HV patients are not only caused by physical deformity but also by modified neural control strategies, possibly to alleviate discomfort and to accommodate the foot deformity. Our results suggest that dynamic evaluation of the whole foot and consideration of foot pain are necessary for the functional assessment of foot pressure in HV patients. The foot balance changes have important clinical implications.

Walking velocity and lower limb coordination in hemiparesis - Corrected Proof

2012-05-01

Abstract: Background/objective: Gait training at fast speed has been suggested as an efficient rehabilitation method in hemiparesis. We investigated whether maximal speed walking might positively impact inter-segmental coordination in hemiparetic subjects.Methods: We measured thigh–shank and shank–foot coordination in the sagittal plane during gait at preferred (P) and maximal (M) speed using the continuous relative phase (CRP), in 20 healthy and 27 hemiparetic subjects. We calculated the root-mean square (CRPRMS) and its variability (CRPSD) over each phase of the gait cycle. A small CRPRMS indicates in-phasing, i.e. high level of synchronization between two segments along the gait cycle. A small CRPSD indicates high stability of the inter-segmental coordination across gait cycles.Results: Increase from preferred to maximal speed was 57% in healthy and 49% in hemiparetic subjects (difference NS). In healthy subjects, the main change was shank–foot in-phasing at stance (CRPShank–Foot/RMS, P, 98±10; M, 67±12, p<0.001). In hemiparetic subjects, we also found shank–foot in-phasing at late stance bilaterally (non-paretic CRPShank–Foot/RMS, P, 37±9; M, 29±8, p<0.001; paretic CRPShank–Foot/RMS, P, 38±13; M, 32±12, p<0.001), and thigh–shank in-phasing at mid-stance in the non-paretic limb (CRPThigh–Shank/RMS, P, 57±9; M, 49±9, p<0.001). CRPThigh–Shank variability diminished in the paretic limb (CRPThigh–Shank/SD, P, 18.3±6.3; M, 16.1±5.2, p<0.001).Conclusion: During gait velocity increase in hemiparesis, there is improvement of thigh–shank coordination stability in the paretic limb and of shank–foot synchronization at late stance bilaterally, which optimizes the propulsive phase similarly to healthy subjects. These findings may add incentive for rehabilitation clinicians to explore maximal velocity gait training in hemiparesis.

Spatiotemporal variability during gait initiation in Parkinson's disease - Corrected Proof

2012-04-30

Highlights: ► We investigate variability of gait initiation in persons with Parkinson's disease and their healthy peers. ► Persons with PD demonstrate higher variability in step length and step time during gait initiation. ► Gait initiation variability did not differ between disease stages in persons with Parkinson's disease.Abstract: During gait initiation (GI), consistency of foot placement while stepping is important in making successful transitions from a state of stable static posture to an unstable state of dynamic locomotion. In populations characterized by gait dysfunction and postural instability, such as persons with Parkinson's disease (PD), the ability to generate a consistent stepping pattern during GI may be essential in the prevention of falls. However, little is known about GI variability in persons with PD as compared to their healthy elderly peers. Therefore, this study investigated spatiotemporal variability during the first two steps of GI in 46 persons with idiopathic PD and 49 healthy age-matched adults. Stepping characteristics, including the length, width, and time of the first two steps of GI as well as their coefficients of variation (CV) were compared between groups. Persons with PD initiated gait with significantly shorter steps (swing step length=.463 vs. .537m, stance step length=.970 vs. 1.10m) and higher variability in step length (swing step CV=8.82 vs. 5.45, stance step CV=6.76 vs. 3.61). Persons with PD also showed significantly higher variability in the time of the swing step (swing step CV=10.0 vs. 7.4). GI variability did not differ significantly between disease stages in persons with PD. Because greater variability in these measures during gait is related to an increased risk of falls, we propose that higher GI variability may play a considerable role in falls frequently observed during transitions from quiet standing in PD.

Crouched posture maximizes ground reaction forces generated by muscles - Corrected Proof

Hoa X. Hoang, Jeffrey A. Reinbolt — 2012-04-27

Highlights: ► We used musculoskeletal modeling and optimization to investigate one possible advantage to crouch gait. ► We placed an OpenSim gait model in 45 different postures from upright to crouch during the stance phase. ► We maximized horizontal ground reaction forces in eight compass directions (e.g., force profile) by adjusting muscle forces. ► The largest force profile areas were found for postures from mild crouch (in initial stance) to crouch (in final stance). ► The ability to generate large force profiles represents a mechanical advantage of adopting a crouched posture.Abstract: Crouch gait decreases walking efficiency due to the increased knee and hip flexion during the stance phase of gait. Crouch gait is generally considered to be disadvantageous for children with cerebral palsy; however, a crouched posture may allow biomechanical advantages that lead some children to adopt a crouch gait. To investigate one possible advantage of crouch gait, a musculoskeletal model created in OpenSim was placed in 15 different postures from upright to severe crouch during initial, middle, and final stance of the gait cycle for a total of 45 different postures. A series of optimizations was performed for each posture to maximize transverse plane ground reaction forces in the eight compass directions by modifying muscle forces acting on the model. We compared the force profile areas across all postures. Larger force profile areas were allowed by postures from mild crouch (for initial stance) to crouch (for final stance). The overall ability to generate larger ground reaction force profiles represents a mechanical advantage of a crouched posture. This increase in muscle capacity while in a crouched posture may allow a patient to generate new movements to compensate for impairments associated with cerebral palsy, such as motor control deficits.

Correlation between anatomic foot and ankle movement measured with MRI and with a motion analysis system - Corrected Proof

C. Marquez-Barrientos, X.C. Liu, R. Lyon, C. Tassone, J. Thometz, S. Tarima — 2012-04-27

Highlights: ► The six segment foot model can be correlated using MRI to underlying bone motion at three different joints in the foot at several positions. ► Underlying bone motion at the Calcaneus–Cuboid joint may not be reliably tracked with the six segment foot model. ► The six segment foot model can be used in the pediatric population.Abstract: Several studies have attempted to measure how well external markers track internal bone movement using pins drilled into the foot, but this is too invasive for the pediatric population. This study investigated how well a six segment foot model (6SFM) using external markers was able to measure bone movement in the foot compared to MRI measurements. The foot was moved into different positions using a plastic foot jig and measurements were taken with both systems. The aims were to: (1) Look at the correlation between movement tracked with an Electronic Motion Tracking System (EMTS) and by measurements derived from MRI images, specifically the principal intercept angles (PIAs) which are the angles of intersection between principal axes of inertia of bone volumes. (2) To see how well external motion measured by the 6SFM could predict PIAs. Four bone pairs had their movement tracked: Tibia–Calcaneus, Calcaneus–Cuboid, Navicular–1st Metatarsal, and 1st Metatarsal–Hallux. The results showed moderate correlation between measured PIAs and those predicted at the Tibia–Calcaneus, Navicular–1st Metatarsal, and 1st Metatarsal–Hallux joints. Moderate to high correlation was found between the PIA and movement in a single anatomic plane for all four joints at several positions. The 6SFM using the EMTS allows reliable tracking of 3D rotations in the pediatric foot, except at the Calcaneus–Cuboid joint.

Regional plantar pressure during walking, stair ascent and descent - Corrected Proof

Smita Rao, Sylvester Carter — 2012-04-26

Abstract: Regional plantar pressures during stair walking may be injurious in at risk populations. However, limited data are available examining the reliability of plantar pressure data collected during stair walking. The aims of this study were three fold; to assess the reliability of the plantar pressure data recorded during stair walking, to assess the effects of level ground and stair walking on plantar loading, and to develop regression equations to predict regional plantar pressures in stair walking from those collected on level ground. Fifteen subjects without conditions affecting their ability to walk on level surfaces or stairs were recruited. Each participant performed at least 10 steps in level ground and stair walking while plantar pressure data were recorded in six foot regions. Reliability was assessed using Intraclass Correlation Coefficient. A repeated measures ANOVA was used to assess the effect of activity on plantar pressure, and a linear regression was used to predict forefoot loading during stair walking. A reliability of 0.9 was achieved within 10 steps in all foot regions, with the forefoot requiring fewer steps. Plantar pressures were influenced by both, foot region and activity, with the heel and forefoot regions generally experiencing lower peak pressures and maximal forces during stair walking than level ground walking. The regression equations predicting peak pressure during stair walking accounted for between 37% and 70% of the variance of the stair walking data. These findings establish the reliability of plantar pressure data collected during stair walking. Future studies should investigate these parameters in clinical populations.

WiiFit™ Plus balance test scores for the assessment of balance and mobility in older adults - Corrected Proof

Rebecca J. Reed-Jones, Sandor Dorgo, Maija K. Hitchings, Julia O. Bader — 2012-04-25

Highlights: ► WiiFit™ balance tests do not correlate with standardized functional balance, mobility and fitness tests. ► Wii balance score does correlate with visual processing speed as measured by Useful Field of View. ► WiiFit™ may provide advantageous information supplementary to standard functional mobility and balance tests. ► Caution should be used when using the WiiFit™ balance tests in isolation to test balance ability.Abstract: The Nintendo Wii™ is becoming an increasingly popular technology for the training and assessment of balance in older adults. Recent studies have shown promising results for its use in fall prevention. However, it is not clear how scores on the WiiFit™ balance games relate to current standardized tests of balance and mobility. The purpose of this study was to evaluate the relationship between WiiFit™ Plus balance tests, and standardized tests of older adult fitness, balance, mobility, self-reported balance confidence, and visual attention and processing. Results from 34 older adult participants indicate that WiiFit™ balance tests do not correlate well with standardized functional balance, mobility and fitness tests. However, the Wii balance score, as measured by the Basic Balance Test of the WiiFit™, does correlate with visual processing speed as measured by the Useful Field of View (UFOV®) test. These results indicate that WiiFit™ balance tests may provide advantageous information supplementary to information obtained through standard functional mobility and balance tests; however, caution should be used when using the WiiFit™ balance tests in isolation. Further research is necessary as these technologies become widely used in clinical and home settings for balance training and assessment.

Correlation of radiographic and pedobarograph measurements in planovalgus foot deformity - Corrected Proof

Muayad Kadhim, Laurens Holmes, Freeman Miller — 2012-04-23

Highlights: ► MMF and heel impulse correlate with radiographic indices in CP planovalgus deformity. ► Foot radiograph may explain part of pedobarograph changes in CP planovalgus deformity. ► Talar head coverage radiographic indices can predict the severity of planovalgus in CP.Abstract: Planovalgus foot deformity is common in children with cerebral palsy. Several pathologies contribute to the deformity. It begins with the lateral displacement of the navicular and the talar head becomes uncovered and prominent in the medial side of the midfoot. The purpose of this study was to assess the correlation between the radiographic and the pedobarographic measurements and the ability to predict foot pressure components using radiographic measurement. The patient sample included 43 patients with cerebral palsy who were ambulatory and had planovalgus foot deformity (76 feet). Medial midfoot pressure showed correlation with talonavicular uncoverage index, talonavicular angle, medial arch angle, Meary angle, and lateral talocalcaneal angle. Heel impulse showed negative correlation with talonavicular uncoverage index and talonavicular angle. Simple linear regression was used to assess the relationship between radiographic and foot pressure component measurements. For every unit change in talonavicular uncoverage index, the predicted value of medial midfoot pressure was [9.9+27 (talonavicular uncoverage index)]. This equation accounted for 17.9% of the changes in the medial midfoot pressure. Tibial foot angle and maximum knee extension also contributed to the heel impulse. The radiographic indices of the planovalgus foot can explain the changes in some foot pressure components.

Potential of lower-limb muscles to accelerate the body during cerebral palsy gait - Corrected Proof

2012-04-23

Highlights: ► This study evaluated lower-limb muscle function in 18 cerebral palsy patients and 10 controls. ► Computational modelling was used to assess each muscle's potential to accelerate the body. ► Significant differences in potential accelerations were displayed between crouch, jump and normal gait patterns. ► The vertical ‘support’ potential of gluteus medius was significantly reduced in crouch and jump gait.Abstract: Two of the most common gait patterns in children with spastic diplegic cerebral palsy (CP) are termed ‘crouch gait’ and ‘jump gait’. While outcomes of surgical interventions designed to improve functional mobility are generally positive, many children displaying these gait patterns show minimal or no improvement post-surgery. A poor response to treatment may be partially attributable to incorrect interpretations of muscle function. Computational techniques that assess muscle function may help address this issue, but before studying specific surgeries, the gait patterns themselves must be better understood. The aim of this study was to identify differences in lower-limb muscle function when comparing crouch, jump and able-bodied gait patterns by quantifying the potential of lower-limb muscles to accelerate the body's center of mass. A muscle's potential acceleration was defined as the acceleration induced by a unit of muscle force. Dynamic simulations of walking using musculoskeletal models were developed for eight children with crouch gait, ten with jump gait, and ten controls. There were significant differences (p<0.05) in muscle potential accelerations between crouch and able-bodied gait patterns, and between jump and able-bodied gait patterns, for most of the major muscles of the hip, knee, and ankle. One important outcome was the identification of the significantly reduced potential of gluteus medius to extend the hip in both crouch gait and jump gait. Potential acceleration analyses appear to be suitable for evaluating differences between common gait patterns and may also be applied to study the effects of surgical treatments. The results of such studies may lead to improved treatment outcomes for individuals with impaired mobility.

The influence of heel height on patellofemoral joint kinetics during walking - Corrected Proof

Kai-Yu Ho, Mark G. Blanchette, Christopher M. Powers — 2012-04-23

Highlights: ► The purpose of this study was to determine if heel height increases patellofemoral joint loading during walking. ► Patellofemoral joint stress was found to increase with increasing heel height. ► The increased patellofemoral joint stress was driven mainly by an increase in patellofemoral joint reaction force. ► This finding suggests that wearing high-heeled shoes may be associated with the development of patellofemoral pain. ► Heel height should be taken into consideration while prescribing footwear for individuals with patellofemoral symptoms.Abstract: Although wearing high-heeled shoes has long been considered a risk factor for the development for patellofemoral pain (PFP) in women, patellofemoral joint kinetics during high-heeled gait has not been examined. The purpose of this study was to determine if heel height increases patellofemoral joint loading during walking. Eleven healthy women (mean age 25.0±3.1 yrs) participated. Lower extremity kinematics and kinetics were obtained under 3 different shoe conditions: low heel (1.27cm), medium heel (6.35cm), and high heel (9.53cm). Patellofemoral joint stress was estimated using a previously described biomechanical model. Model outputs included patellofemoral joint reaction force, patellofemoral joint stress and utilized contact area as a function of the gait cycle. One-way ANOVAs with repeated measures were used to compare the model outputs and knee joint angles among the 3 shoe conditions. Peak patellofemoral joint stress was found to increase significantly (p=0.002) with increasing heel height (low heel: 1.9±0.7MPa, medium heel: 2.6±1.2MPa, and high heel: 3.6±1.5MPa). The increased patellofemoral joint stress was mainly driven by an increase in joint reaction force owing to higher knee extensor moments and knee flexion angles. Our findings support the premise that wearing high-heeled shoes may be a contributing factor with respect to the development of PFP.

The relative contributions of the prosthetic and sound limb to balance control in unilateral transtibial amputees - Corrected Proof

Carolin Curtze, At L. Hof, Klaas Postema, Bert Otten — 2012-04-23

Highlights: ► We compared the contribution of the hip and ankle joints to balance control following waist-pull perturbations. ► Perturbations in backward/forward direction are recovered mainly by the ankle strategy. ► Amputees compensate for the absence of active ankle control in the prosthetic limb by increasing the ankle moment in the sound limb. ► The passive properties of the prosthetic foot contribute to balance control. ► Amputees and controls resist perturbations in medio-lateral direction by generating the necessary hip moments.Abstract: In unilateral transtibial amputees maintenance of standing balance is compromised due to the lack of active ankle control in the prosthetic limb. The purpose of this study is to disentangle the contribution of the prosthetic and sound limb to balance control following waist-pull perturbations. We compared the contribution of the hip and ankle joints to balance control of 15 unilateral transtibial amputees and 13 able-bodied controls after been externally perturbed through release of a pulling force. Perturbations were applied in four different directions. Outcome measure was the proportion of joint moment integrated over time generated by the hip and ankle joints in order to restore static stability after perturbation. Analyses revealed that perturbations in backward/forward direction were recovered mainly by the ankle strategy. The amputees compensated for the absence of active ankle control in the prosthetic limb by increasing the ankle moment in the sound limb. Interestingly, the passive properties of the prosthetic foot contributed to balance control, which has important implications for prosthetic fitting and standing stability in lower limb amputees. Amputees and controls resisted perturbations in medio-lateral direction by generating the necessary hip moments. Finally, these findings are discussed with respect to prosthetic design and rehabilitation processes.

Biomechanical strategies to accommodate expected slips in different directions during walking - Corrected Proof

Anderson Souza Castelo Oliveira, Dario Farina, Uwe Gustav Kersting — 2012-04-23

Highlights: ► The first peak of vertical GRF is reduced in catch trials after experiencing slips in different directions. ► EMG of leg muscles is selectively altered during the first half of stance. ► Peroneus longus is affected by both frontal und sagittal plane perturbations.Abstract: The aim of the study was to verify whether heel kinematics, ground reaction forces and electromyography (EMG) during walking are affected when anticipating slips in anterior–posterior (AP) and medial–lateral directions (ML). Eight healthy men walked through a 7-m walkway, stepping on a robotic force platform. Initially, baseline (BASE) gait mechanics were assessed with the platform at rest. Subsequently, two sets of randomized perturbations (10-cm translations with at different platform movement velocities) in the AP and ML direction were applied. Perturbations were interspersed with unperturbed walking (i.e., catch-trials C-AP and C-ML). Heel accelerations, ground reaction forces and activities from the perturbed leg and trunk muscles were analyzed. EMG was analysed in four epochs: PRE (−100ms to heel strike [HS]), EARLY (HS to 150ms after HS), MID (150–300ms after HS) and LATE (300ms to toe-off). Comparisons were made between BASE, C-AP and C-ML. The first peak of the vertical force component (Fz) was decreased for C-AP and C-ML (p<0.05) but no changes were found for braking and propulsion impulses. EMG showed effects of expected slips on tibialis anterior, gastrocnemius lateralis, soleus and peroneus longus, especially for EARLY and MID epochs, with direction-specific increases in activity. In conclusion, expected slips in different directions determine only marginal changes in terms of kinetics and heel kinematics, but selective activation after HS indicates that direction-dependent strategies are adopted when anticipating perturbations.

Arm training in standing also improves postural control in participants with chronic stroke - Corrected Proof

Sandy McCombe Waller, Michelle G. Prettyman — 2012-04-23

Highlights: ► We examine the implicit training of postural control during arm training in standing. ► Gains are seen in both quantitative and functional measures of postural control. ► Arm training in standing improves both arm function and postural control.Abstract: Purpose: To prove the concept that postural control will improve without specific balance control training during arm training in standing with individuals with chronic stroke.Methods: Nine participants (mean age 64±7) received training involving hand orthotic assisted grasp, reach and release in standing 1h, 3×’s/week for 6weeks. Training focused on task completion with no explicit instructions provided for postural alignment, weight shift or balance strategy. Testing consisted of quantified measures using NeuroCom™ Balance Master, Berg Balance Scale (BBS) and Activities-specific Balance Confidence Scale (ABC).Results: Post training participants demonstrate increased (p<.05) composite stability scores for sensory organization testing (mean 71.55±12.7–75.55±11). Velocity and directional control of COP weight shift improved for all 9 subjects with 6/9 achieving 100% target acquisition. Directional control improved (p<.05) for medial/lateral movements for all speeds and composite score. Anterior/posterior rhythmic weight shifting increased significantly in COP velocity control at moderate and fast velocities and composite score. Increases in mean BBS (p<.01) from 41.33±10.1–46.88±8.03 exceeded the clinically important cutoff for the scale. Balance confidence improved with ABC mean scores 70.22±14.5–79.55±12.86 (p<.05). Seven participants demonstrated changes above the minimally important difference for this scale.Conclusions: Postural control improved following task oriented arm training in standing without explicit postural control goals, instruction or feedback challenging current training paradigms of isolated postural control training with conscious attention directed to center of pressure location and movement.

Balance impairment in people with multiple sclerosis: Preliminary evidence for the Balance Evaluation Systems Test - Corrected Proof

Jesse V. Jacobs, Susan L. Kasser — 2012-04-23

Highlights: ► Subjects with and without multiple sclerosis (MS) were evaluated on the Balance Evaluation Systems Test (BESTest). ► The BESTest was validated against lab measures of postural control, and the subjects’ disease severity and fall history. ► Subjects with MS exhibited significantly lower BESTest scores than subjects without MS. ► BESTest scores significantly associated with lab measures, disease severity, and fall history. ► The BESTest offers a valid clinical assessment of balance impairments in people with MS.Abstract: This study examined the validity of the Balance Evaluation Systems Test (BESTest) to identify balance impairments in people with multiple sclerosis (MS) by evaluating differences in BESTest performance between people with and without MS. We also assessed the BESTest's validity by correlation with objective measures of postural performance as well as with disease severity and fall status. Thirteen subjects with MS (Expanded Disability Status Scale; EDSS: 0–4.5) and 13 matched subjects without MS were evaluated on the BESTest, asked about fall history, and assessed by force plates and motion capture as they performed laboratory tasks of step initiation, forward leaning to the limits of stability, and postural responses to rotations of the support surface. Compared to subjects without MS, subjects with MS exhibited lower total BESTest scores (mean (95%) score for subjects with MS=91 (83–99); subjects without MS=105 (104–107)) as well as section scores pertaining to mechanical constraints, limits of stability, anticipatory postural adjustments, and gait. BESTest scores significantly correlated with objective laboratory measures of step velocity during step initiation (Pearson r2=0.48, P<0.01) as well as center-of-pressure displacements during both the leaning (Pearson r2=0.55, P<0.005) and postural-response tasks (Pearson r2=0.76, P<0.0001). BESTest total scores were 92% accurate to identify fallers and non-fallers, and BESTest scores significantly correlated with EDSS scores (Spearman's rho=0.85, P<0.0005). Thus, the BESTest provides a valid clinical assessment of balance impairments in people with MS.

How an acute mastering of balance on a seesaw can improve the relationship between “static” and “dynamic” upright postural control - Corrected Proof

Patrice R. Rougier — 2012-04-19

Highlights: ► Standing on a seesaw modifies the available sensory information and amplifies the motor command with the translational-rotational movement. ► Both standing on a firm surface and standing on a seesaw share close biomechanical and neurophysiological principles. ► Comparing the two tasks can be difficult because of discrepancies in the ability to rapidly master the new seesaw constraints. ► Whereas no correlation was found before training, several significant linear correlations were found after pitch training. ► These results highlight the role played by short-term adaptation in standing performance.Abstract: Postural control ability has been widely evaluated using undisturbed upright stance protocols. However, standing on a seesaw may offer additional insights due to changes in the available sensory information and the amplification of the motor command resulting from the translational and rotational movement of the device. These two tasks share close biomechanical and neurophysiological principles. To highlight their possible linkage, 32 young healthy adults participated in this study, which consisted of testing postural performance while standing on a firm surface or on a seesaw producing rolling or pitching movements. The results showed increased CP displacements along the seesaw's pitching or rolling axis and also along the perpendicular axis. However, comparing the two tasks can be difficult because of discrepancies in the ability to rapidly master the new constraints brought about by the seesaw. To highlight the role played by adaptation, 15 subjects of the whole sample participated in a complementary protocol consisting of a 20-min training session aimed at improving the mastery of the seesaw producing pitch motions. The relationship between the amplitudes of the CP displacements between “static” and “dynamic” tasks was investigated. Interestingly, whereas no statistically significant linear correlation was found before training, several significant correlations were found after pitch training for AP displacements. By emphasizing the key role played by short-term adaptation in standing performance, these results are likely to have potential implications regarding the conception of standardized tests aimed at evaluating postural ability in healthy or disabled subjects.

Accelerometry-based gait analysis, an additional objective approach to screen subjects at risk for falling - Corrected Proof

R. Senden, H.H.C.M. Savelberg, B. Grimm, I.C. Heyligers, K. Meijer — 2012-04-18

Highlights: ► Gait characteristics are different for elderly with different Tinetti scores. ► Speed has best discriminative power to classify elderly according to Tinetti score. ► Fall risk related subtleties in gait are not captured by subjective assessment. ► Objective gait assessment is of added value in fall risk screening.Abstract: This study investigated whether the Tinetti scale, as a subjective measure for fall risk, is associated with objectively measured gait characteristics. It is studied whether gait parameters are different for groups that are stratified for fall risk using the Tinetti scale. Moreover, the discriminative power of gait parameters to classify elderly according to the Tinetti scale is investigated. Gait of 50 elderly with a Tinneti>24 and 50 elderly with a Tinetti≤24 was analyzed using acceleration-based gait analysis. Validated algorithms were used to derive spatio-temporal gait parameters, harmonic ratio, inter-stride amplitude variability and root mean square (RMS) from the accelerometer data. Clear differences in gait were found between the groups. All gait parameters correlated with the Tinetti scale (r-range: 0.20–0.73). Only walking speed, step length and RMS showed moderate to strong correlations and high discriminative power to classify elderly according to the Tinetti scale. It is concluded that subtle gait changes that have previously been related to fall risk are not captured by the subjective assessment. It is therefore worthwhile to include objective gait assessment in fall risk screening.

Gait dynamics following variable and constant speed gait training in individuals with chronic stroke - Corrected Proof

Christopher K. Rhea, Clinton J. Wutzke, Michael D. Lewek — 2012-04-16

Highlights: ► Stroke negatively influences the control of gait and it is unclear which interventions may restore neuromotor control. ► Gait dynamics provide an additional way to examine neuromotor control compared to traditional summary metrics. ► A variable speed treadmill training intervention was used to determine if gait dynamics could be positively influenced. ► No differences between the intervention and a constant speed condition were observed. ► Future interventions will be designed to alter gait dynamics at the stride level and across multiple training sessions.Abstract: Variable practice may be beneficial for learning novel motor patterns. The purpose of this study was to determine the effect of a variable practice intervention during treadmill walking on the dynamic properties of gait. Using a counterbalanced design, 16 subjects with hemiparesis following chronic stroke performed 20min of treadmill walking in constant speed training (CST) and variable speed training (VST) conditions. The dynamic properties of the hip and knee sagittal plane angles for two minutes before (pre-data) and two minutes after (post-data) CST and VST were examined using detrended fluctuation analysis and sample entropy. A main effect for time was observed for sample entropy of the knee angle; no other differences were observed between the pre/post data for the CST or VST conditions. While variable practice conditions are intended to promote movement errors for improved learning, we were unable to detect immediate changes in movement variability as a function of practice condition following a single session of gait training for individuals post-stroke.

Kinematic assessment of stereotypy in spontaneous movements in infants - Corrected Proof

2012-04-16

Highlights: ► Kinematics of infants were recorded at the age of 3 months. ► We investigated the meaning of stereotyped movements in infant motor development. ► At the age of 24 months 10 infants had developed cerebral palsy (CP), 56 had not. ► The presence of self-similar movements of the upper limb correlated with CP. ► Our quantitative score identified CP cases with 90% sensitivity and 96% specificity.Abstract: Movement variation constitutes a crucial feature of infant motor development. Reduced variation of spontaneous infant movements, i.e. stereotyped movements, may indicate severe neurological deficit at an early stage. Hitherto evaluation of movement variation has been mainly restricted to subjective assessment based on observation. This article introduces a method for quantitative assessment yielding an objective definition of stereotyped movements which may be used for the prognosis of neurological deficits such as cerebral palsy (CP).Movements of 3-month-old infants were recorded with an electromagnetic tracking system facilitating the analysis of joint angles of the upper and lower limb. A stereotypy score based on dynamic time warping has been developed describing movements which are self-similar in multiple degrees of freedom. For clinical evaluation, this measure was calculated in a group of infants at risk for neurological disorders (n=54) and a control group of typically developing children (n=21) on the basis of spontaneous movements at the age of 3 months. The stereotypy score was related to outcome at the age of 24 months in terms of CP (n=10) or no-CP (n=53). Using the stereotypy score of upper limb movements CP cases could be identified with a sensitivity of 90% and a specificity of 96%. The corresponding score of the leg movements did not allow for valid discrimination of the groups.The presented stereotypy feature is a promising candidate for a marker that may be used as a simple and noninvasive quantitative measure in the prediction of CP. The method can be adopted for the assessment of infant movement variation in research and clinical applications.

Feedforward postural control in individuals with multiple sclerosis during load release - Corrected Proof

Vennila Krishnan, Neeta Kanekar, Alexander S. Aruin — 2012-04-09

Highlights: ► Feedforward postural control is studied in persons with multiple sclerosis (MS). ► Self-initiated load-release paradigm is used to perturb standing balance. ► Anticipatory postural adjustments are delayed and reduced in magnitude in MS. ► Mildly impaired individuals with MS demonstrate early changes in postural control.Abstract: The aim of the present study was to investigate the organization of anticipatory postural adjustments (APAs) in individuals with multiple sclerosis (MS) during self-initiated perturbation in the sagittal plane. Eleven individuals with MS and eleven age-and-gender matched healthy controls were asked to hold a 2.27kg load in the extended arms and release it using fast arm abduction movements. Electrical activity of six leg and trunk muscles as well as displacements of the center of pressure (COP) were recorded. The results indicate that individuals with MS (1) demonstrate a reduced magnitude of APAs, (2) delayed latency of APAs and (3) smaller anticipatory COP displacement as compared to healthy control subjects. Moreover, in spite of individuals with MS being mildly affected, their balance capacity was significantly diminished. Thus, the outcome of this study demonstrates the underlying impairment in anticipatory postural control of individuals with MS and provides a background for development of rehabilitation strategies focused on balance restoration in this population.

The influence of body weight, body mass index and gender on plantar pressures: Results of a cross-sectional study of healthy children's feet - Corrected Proof

Jill Phethean, Christopher Nester — 2012-04-09

Highlights: ► We studied plantar pressure in 98 children aged 4–7 years. ► We investigated whether plantar pressure was related to BMI, body weight and gender. ► Girls and boys have comparable plantar pressure. ► Plantar pressure was not strongly related to BMI or body weight. ► Plantar pressure should not be normalised by BMI or body weight.Abstract: The purpose of this study was to determine if plantar pressure data in 4–7 year old children with normal development: (1) required normalising by body mass and/or body mass index and (2) should be separated or pooled for boys and girls. The outcome will guide the management of plantar pressure data in future work investigating changes in plantar pressure distribution with increasing age. In a cross-sectional design, 98 British children (45 girls) with no orthopaedic, neurological or developmental disorders provided plantar pressure measurements during walking. Peak plantar pressure and plantar pressure time integrals were obtained from nine areas under the foot: calcaneus, medial and lateral midfoot, each of the five metatarsals and the hallux. Body weight and body mass index demonstrated low and weak degrees of association (r≤0.48, p<0.05) with plantar pressure data. Boys and girls showed no difference in plantar pressures (p<0.05). Plantar pressure data for 4–7 year olds does not require normalisation with body mass or body mass index, and can be pooled for boys and girls.

Do somatosensory conditions from the foot and ankle affect postural responses to plantar-flexor muscles fatigue during bipedal quiet stance? - Corrected Proof

Petra Hlavackova, Nicolas Vuillerme — 2012-04-05

Highlights: ► We assessed postural responses to plantar-flexor muscle fatigue during bipedal standing. ► Three conditions were tested: normal, altered and improved foot and ankle somatosensation. ► We observed an increased reliance on foot and ankle somatosensation with muscle fatigue. ► These findings are discussed in terms of sensory re-weighting mechanisms for controlling posture.Abstract: The present study investigated the effects of somatosensory conditions at the foot and ankle on postural responses to plantar-flexor muscle fatigue during bipedal quiet stance. Twenty-two young healthy adults were asked to stand upright as still as possible with their eyes closed in three somatosensory conditions (normal, altered and improved) both prior to and after exercises inducing plantar-flexor muscle fatigue. In the normal condition, the postural task was executed on a firm support surface constituted by the force platform. In the altered condition, a 2-cm thick foam support surface was placed under the subjects’ feet. In the improved condition, increased cutaneous feedback at the foot and ankle was provided by strips of athletic tape applied across both their ankle joints. Muscle fatigue was induced in the plantar-flexor muscles of both legs through the execution of a repeated standing heel raise exercise. Centre of foot pressure displacements were recorded using a force platform. Results showed that plantar-flexor muscle fatigue yielded increased centre of foot pressure displacements under normal foot and ankle sensory conditions. Furthermore, this effect was exacerbated under altered foot and ankle sensory conditions and mitigated under improved foot and ankle sensory conditions. Altogether, the present findings suggested an increased reliance on somatosensory information from the foot and ankle for controlling upright posture in the presence of plantar-flexor muscle fatigue.

Integrated kinematics–kinetics–plantar pressure data analysis: A useful tool for characterizing diabetic foot biomechanics - Corrected Proof

2012-04-05

Highlights: ► Simultaneous 3-dimensional kinematics kinetics and pressure analysis of 3 foot's subsegments: hindfoot, midfoot, forefoot. ► Comparison between controls and neuropathic subjects’ foot biomechanics. ► A system that integrates 3 commercial devices: a pressure platform, a force platform and a stereophotogrammetric system. ► Data were collected during gait on 24 subjects: 12 controls and 12 diabetic neuropathics. ► Statistically significant alterations on neuropathic subjects: midfoot's excessive pressure, forces increased dorsiflexion.Abstract: The fundamental cause of lower-extremity complications in diabetes is chronic hyperglycemia leading to diabetic foot ulcer pathology. While the relationship between abnormal plantar pressure distribution and plantar ulcers has been widely investigated, little is known about the role of shear stress. Moreover, the mutual relationship among plantar pressure, shear stress, and abnormal kinematics in the etiology of diabetic foot has not been established. This lack of knowledge is determined by the lack of commercially available instruments which allow such a complex analysis. This study aims to develop a method for the simultaneous assessment of kinematics, kinetics, and plantar pressure on foot subareas of diabetic subjects by means of combining three commercial systems. Data were collected during gait on 24 patients (12 controls and 12 diabetic neuropathics) with a motion capture system synchronized with two force plates and two baropodometric systems. A four segment three-dimensional foot kinematics model was adopted for the subsegment angles estimation together with a three segment model for the plantar sub-area definition during gait. The neuropathic group exhibited significantly excessive plantar pressure, ground reaction forces on each direction, and a reduced loading surface on the midfoot subsegment (p<0.04). Furthermore the same subsegment displayed excessive dorsiflexion, external rotation, and eversion (p<0.05). Initial results showed that this methodology may enable a more appropriate characterization of patients at risk of foot ulcerations, and help planning prevention programs.

Catch! Movement kinematics of two-handed catching in boys with Developmental Coordination Disorder - Corrected Proof

2012-04-05

Highlights: ► Sequencing and symmetry of two-handed catching in boys with DCD was examined. ► They displayed longer movement times and altered upper limb kinematics. ► There was greater variability in joint range of motion. ► The action was more asymmetrical. ► These inefficiencies in technique are likely to compromise catching performance.Abstract: Purpose: To quantify two-handed catching in boys with Developmental Coordination Disorder (DCD) by examining sequencing of the upper limb and trunk segments, and degree of symmetry.Method: Thirteen boys with DCD ( years±0.68) and 13 Controls ( years±0.68) participated. Children performed 10 two-handed central catching trials, with the best five trials selected for analysis.Results: The DCD group displayed greater variability in range of motion across all joint rotations in the catch phase. Specifically, increased shoulder flexion, thorax extension and elbow extension. Although the initiation of segmental movement occurred in the same order for the two groups, the DCD group initiated wrist extension considerably earlier. The DCD group also exhibited significant asymmetry in elbow flexion–extension.Conclusion: Despite success in performing this simple catching task (88% successful), the DCD group displayed an inefficient, variable and less symmetrical catching technique.

Influence of constrained visual and somatic senses on controlling centre of mass during sit-to-stand - Corrected Proof

2012-04-05

Highlights: ► We examined sit-to-stand movement under constraining vision and somatic senses. ► The variability of velocity and position of Center of mass (COM) were computed. ► Velocity's variability in two major directions decreased when constraining two senses. ► Position's variability in the right-left direction increased. ► The nervous system sets priorities for COM control in the moving direction.Abstract: This study aimed to investigate the manner in which healthy individuals execute robust whole body movements despite unstable body structure from the perspective of perception–action coupling. Twelve healthy adults performed sit-to-stand (STS) movements under conditions of constrained visual and somatic senses. During this movement, centre of mass (COM) of the body in the anterior–posterior, upward–downward and right–left directions was computed. The conditions of perceptual constraint were set as vision-restricted, somatosensory-restricted, vision- and somatosensory-restricted, and normal conditions. To evaluate COM control under these perceptual constraints, the variability in position and velocity of COM were assessed. The variabilities in COM velocity in the anterior–posterior and upward–downward directions decreased around the lift-off period only when both vision and somatic senses were constrained, whereas the variability of the COM position in the right–left direction increased under the somatosensory-restricted condition. Our findings suggested that control of COM velocity was enhanced in the major moving directions (anterior and upward directions) around the lift-off period during STS when both modalities of perception with regard to postural orientation were constrained. These motor regulations with perceptual constraints facilitate better adaptation to changes in body and environmental situations in daily life.

Influence of real and virtual heights on standing balance - Corrected Proof

Taylor W. Cleworth, Brian C. Horslen, Mark G. Carpenter — 2012-04-05

Highlights: ► Postural and psychophysiological factors compared between real and virtual heights. ► Arousal, anxiety and fear increase with height in both real and virtual environments. ► COP amplitude decreases and frequency increases with height in both environments. ► Virtual reality may be a useful tool to study fear and anxiety effects on balance.Abstract: Fear and anxiety induced by threatening scenarios, such as standing on elevated surfaces, have been shown to influence postural control in young adults. There is also a need to understand how postural threat influences postural control in populations with balance deficits and risk of falls. However, safety and feasibility issues limit opportunities to place such populations in physically threatening scenarios. Virtual reality (VR) has successfully been used to simulate threatening environments, although it is unclear whether the same postural changes can be elicited by changes in virtual and real threat conditions. Therefore, the purpose of this study was to compare the effects of real and virtual heights on changes to standing postural control, electrodermal activity (EDA) and psycho-social state. Seventeen subjects stood at low and high heights in both real and virtual environments matched in scale and visual detail. A repeated measures ANOVA revealed increases with height, independent of visual environment, in EDA, anxiety, fear, and center of pressure (COP) frequency, and decreases with height in perceived stability, balance confidence and COP amplitude. Interaction effects were seen for fear and COP mean position; where real elicited larger changes with height than VR. This study demonstrates the utility of VR, as simulated heights resulted in changes to postural, autonomic and psycho-social measures similar to those seen at real heights. As a result, VR may be a useful tool for studying threat related changes in postural control in populations at risk of falls, and to screen and rehabilitate balance deficits associated with fear and anxiety.

An enhanced estimate of initial contact and final contact instants of time using lower trunk inertial sensor data - Corrected Proof

John McCamley, Marco Donati, Eleni Grimpampi, Claudia Mazzà — 2012-04-05

Highlights: ► A method to identify gait events from lower trunk accelerations is proposed. ► Vertical acceleration measured at waist level was processed with a wavelet approach. ► Accuracy of the method was assessed in healthy subjects using an instrumented mat. ► The method proved highly reliable, detecting 100% of the analysed events. ► Average initial and final contact estimate errors were 0.02s and 0.03s, respectively.Abstract: This study introduces a new method of extracting initial and final contact gait time events from vertical acceleration, measured with one waist mounted inertial measurement unit, by means of continuous wavelet transforms. The method was validated on 18 young healthy subjects and compared to two others available in the literature. Of the three methods investigated, the new one was the most accurate at identifying the existence and timing of initial and final contacts with the ground, with an average error of 0.02±0.02s and 0.03±0.03s (approximately 2% and 3% of mean stride duration), respectively.

Interference between walking and a cognitive task is increased in patients with bilateral vestibular loss - Corrected Proof

2012-04-05

Highlights: ► Walking under dual-task conditions is compared between patients with bilateral vestibular loss and healthy subjects. ► Walking speed of patients with bilateral vestibular loss does not differ from controls in single-task condition but it is more affected than controls under dual-task conditions. ► Patients with bilateral vestibular loss do not differ from controls in their cognitive performance in both the single and dual-task conditions. ► Attentional interference between walking and a cognitive task is greater in patients with bilateral vestibular loss than in healthy subjects.Abstract: The aim of this study was to determine whether there is more deterioration in walking under dual-task conditions in patients with bilateral vestibular loss (BVL) than in healthy subjects, as opposed to the findings after unilateral loss. For this purpose, 12 patients with BLV and 12 healthy control subjects performed 3 tasks: walking along a 10-m walkway, counting backwards by two, and both tasks simultaneously. Patients did not differ from controls in their walking speed in the single task condition, or in their cognitive performance in both the single and dual-task conditions. However, walking performance was more affected in patients than in controls under dual-task conditions, as shown by slower gait speed in the dual-task, higher reduction in gait speed from single to dual-task, and lower global dual-score. These findings provide evidence for greater attentional interference between walking and counting in patients with BVL.

Lower limb preference on goal-oriented tasks in unilateral prosthesis users - Corrected Proof

Charla Howard, Chris Wallace, Dobrivoje S. Stokic — 2012-04-05

Highlights: ► Prosthesis users do not consistently use intact leg for support and prosthetic leg for task completion as often believed. ► More experienced prosthesis users are more likely to choose prosthetic leg for support and intact leg for task completion. ► Less defined lower limb preference in prosthetic users may pose a risk for fall when performing activities of daily living.Abstract: The aim of this study was to determine lower limb preference in 31 prosthesis users and 19 able-bodied controls on 11 goal-oriented tasks in free-standing and supported conditions. The action leg used in 6 or more tasks was considered the preferred leg. We hypothesized that the prosthetic leg in amputees would be used as the preferred leg as often as the dominant leg in controls. For prosthesis users in the free-standing condition, 65% used the prosthetic leg as the preferred leg. This was significantly different (p<0.003) from able-bodied controls, where 100% used the dominant leg as the preferred leg. This discrepancy became even more pronounced in the supported condition and was overall more prevalent among those who used prosthesis for more than 10 years. These findings may have implications for therapy and gait training.

Posturo-respiratory synchronization: Effects of aging and stroke - Corrected Proof

Brad D. Manor, Kun Hu, Chung-Kang Peng, Lewis A. Lipsitz, Vera Novak — 2012-04-05

Highlights: ► Spontaneous respiration influences anterioposterior postural sway when standing. ► We introduced “posturo-respiratory synchronization” to quantify this influence. ► Synchronization strength was visually dependent and increased with age and stroke. ► This novel metric may be used as a marker of altered postural control.Abstract: Spontaneous respiration influences the body's center-of-mass when standing. We contend that the healthy postural control system actively adapts to respiration, thereby minimizing its effect on postural sway. We therefore examined the interaction between respiration and postural sway, as measured by center-of-pressure (COP) oscillations, and quantified the extent to which this interaction resulted in “posturo-respiratory synchronization.” We hypothesized that synchronization would be stronger in elderly subjects and those with stroke, and when standing with eyes closed as compared to open, due to alterations in the physiologic mechanisms that normally regulate postural sway. Twenty-five subjects with chronic hemispheric infarction and 38 controls (50–80 years) stood on a force platform for 3min with eyes-open and 3min with eyes-closed. Respiratory flow and COP dynamics were simultaneously recorded. The dominant oscillatory mode of respiration and the corresponding oscillatory modes of anterioposterior and mediolateral COP dynamics were extracted using ensemble empirical mode decomposition. The strength of posturo-respiratory synchronization was quantified from the regularity of instantaneous phase shifts between extracted respiratory and COP oscillations. Significant posturo-respiratory synchronization was only present in the anterioposterior direction. The strength of synchronization increased with age (p<0.01). Closing the eyes increased synchronization strength in both groups (p=0.01), but more so in stroke patients (p=0.01). These observations suggest that a control system actively regulates the effects of respiration on sagittal-plane postural sway, particularly during eyes-open standing. As evidenced by increased posturo-respiratory synchronization with advanced age and central lesion, this novel metric may be used as a clinical marker of altered postural control.

Regulation of whole-body frontal plane balance varies within a step during unperturbed walking - Corrected Proof

Andrew Sawers, Michael E. Hahn — 2012-04-05

Highlights: ► The consistency of active control over lateral balance within a step was assessed. ► Active control of lateral balance was found to vary significantly within a step. ► The greatest degree of active control over lateral balance occurs at heel-strike. ► Greater active control may ensure adequate balance prior to challenging gait events. ► Better resolution of within-step assessment may lead to phase-specific interventions.Abstract: This study sought to determine whether the need to actively control lateral balance is consistent within a step. Variability of the frontal plane COM-Ankle angle was calculated over 50 strides at discrete gait events for twenty-one healthy young adults to quantify active control of lateral balance within a step. Frontal plane COM-Ankle angle variability was found to vary significantly between all gait events, decreasing progressively within a step. This suggests that active control of lateral balance varies significantly within a step and that the greatest degree of active control occurs at heel-strike. The increased active control of lateral balance during heel-strike indicates a degree of preparation to ensure sufficient lateral balance control prior to more challenging events. These results provide insight into the mechanisms of lateral balance control and how to assess and treat locomotor balance control impairments.

Uncontrolled manifold analysis of gait variability: Effects of load carriage and fatigue - Corrected Proof

Xingda Qu — 2012-04-05

Highlights: ► We examined the effects of load carriage and fatigue on gait variability using the uncontrolled manifold analysis. ► Sagittal ⊥UCM was found to increase with the application of high back-carrying load. ► We also found that frontal UCM ratio significantly changed with the application of back-carrying load and fatigue. ► Motor variability in both the sagittal and frontal planes was greater at heel contact versus toe off.Abstract: The uncontrolled manifold (UCM) analysis has been demonstrated to be a powerful tool for understanding motor variability. The purpose of this study was to use the UCM analysis to investigate the effects of load carriage and fatigue on gait variability. Whole-body kinematic data during treadmill walking were collected from 12 healthy male participants when fatigue and load carriage were applied. The task-level variable for the UCM analysis was selected to be the whole-body COM. We chose to analyze the whole-body COM data at two important gait events: right heel contact and right toe off, and the UCM analysis was carried out in the sagittal and frontal planes, separately. The dependent measures were UCM variability measures and UCM ratio. Three-way ANOVA was performed to determine the main and interaction effects of back-carrying load, fatigue, and gait events on the dependent measures. The results showed that frontal UCM ratio significantly changed with the application of back-carrying load and fatigue, indicating that both factors had effects on motor performance in stabilizing the whole-body COM in the frontal plane. These findings can facilitate a better understanding of the nature of motor variability due to load carriage and fatigue.

Speeding up or slowing down?: Gait adaptations to preserve gait stability in response to balance perturbations - Corrected Proof

2012-04-05

Highlights: ► The effect of balance perturbations on walking speed, step length, step frequency, and step width was measured. ► Besides, short-term Lyapunov exponents in the margins of stability were calculated to quantify the risk of falling. ► Subjects did not slow down, but increased step frequency and width and decreased step length in response to the perturbations. ► Subjects became locally less stable, but increased their sideward and backward margins of stability.Abstract: It has frequently been proposed that lowering walking speed is a strategy to enhance gait stability and to decrease the probability of falling. However, previous studies have not been able to establish a clear relation between walking speed and gait stability. We investigated whether people do indeed lower walking speed when gait stability is challenged, and whether this reduces the probability of falling.Nine healthy subjects walked on the Computer Assisted Rehabilitation ENvironment (CAREN) system, while quasi-random medio-lateral translations of the walking surface were imposed at four different intensities. A self-paced treadmill setting allowed subjects to regulate their walking speed throughout the trials. Walking speed, step length, step frequency, step width, local dynamic stability (LDS), and margins of stability (MoS) were measured.Subjects did not change walking speed in response to the balance perturbations (p=0.118), but made shorter, faster, and wider steps (p<0.01) with increasing perturbation intensity. Subjects became locally less stable in response to the perturbations (p<0.01), but increased their MoS in medio-lateral (p<0.01) and backward (p<0.01) direction.In conclusion, not a lower walking speed, but a combination of decreased step length and increased step frequency and step width seems to be the strategy of choice to cope with medio-lateral balance perturbations, which increases MoS and thus decreases the risk of falling.

Coordination of trunk and pelvis in young and elderly individuals during axial trunk rotation - Corrected Proof

Paul S. Sung, Kyung-Joon Lee, Woo-Hyung Park — 2012-04-05

Highlights: ► This study investigated age-related changes in spinal movement control. ► Subjects performed trunk rotation, and angular displacements of the trunk and pelvis was measured. ► Based on angular displacements, relative phase between the trunk and pelvis was calculated. ► Relative phase showed that the older adults moved the two segments as a one unit, compared to the young adults. ► Relative phase also showed that the older adults put more effort into pelvis control to stop the two segments simultaneously.Abstract: It has been well known that complex tasks such as walking and arm reaching can be achieved by the coordination of the trunk and pelvis. However, understanding of the effect of aging on the coordination of the trunk and pelvis during axial trunk rotation is still lacking. The present study examined relative phase of the trunk and pelvis during axial trunk rotation, and compared it between young and older groups. 22 healthy young (age: 23.9±4.6, gender: 11 male and 11 female) and 22 healthy elderly (age: 68.4±4.9, gender: 11 male and 11 female) individuals participated in the experiment and performed axial trunk rotation. Relative phase between the trunk and pelvis was calculated based on the angular displacements of the two segments. The results demonstrated age-related changes in coordination pattern of the trunk and pelvis during axial trunk rotation.

Treadmill gait speeds correlate with physical activity counts measured by cell phone accelerometers - Corrected Proof

2012-04-04

Highlights: ► Trial primary outcome was to determine if measurements from cell phone accelerometers correlated with treadmill walking speed. ► Trial secondary outcome was to determine if the location where the subject kept the cell phone (ankle, hip, wrist, etc.) affected the results. ► Enrollment: 17 young (age 19–35), 19 middle-aged (36–65), 17 aged (66+) community dwelling, independent adults with no functional gait deficits. ► Physical activity counts derived from cell phone accelerometer strongly correlated with gait speed. ► The hip was the best location to place the cell phone; however, all positions yielded suitable models.Abstract: A number of important health-related outcomes are directly related to a person's ability to maintain normal gait speed. We hypothesize that cellular telephones may be repurposed to measure this important behavior in a noninvasive, continuous, precise, and inexpensive manner. The purpose of this study was to determine if physical activity (PA) counts collected by cell phone accelerometers could measure treadmill gait speeds. We also assessed how cell phone placement influenced treadmill gait speed measures. Participants included 55 young, middle-aged, and older community-dwelling men and women. We placed cell phones as a pendant around the neck, and on the left and right wrist, hip, and ankle. Subjects then completed an individualized treadmill protocol, alternating 1min rest periods with 5min of walking at different speeds (0.3–11.3km/h; 0.2–7mi/h). No persons were asked to walk at speeds faster than what they would achieve during day-to-day life. PA counts were calculated from all sensor locations. We built linear mixed statistical models of PA counts predicted by treadmill speeds ranging from 0.8 to 6.4km/h (0.5–4mi/h) while accounting for subject age, weight, and gender. We solved linear regression equations for treadmill gait speed, expressed as a function of PA counts, age, weight, and gender. At all locations, cell phone PA counts were strongly associated with treadmill gait speed. Cell phones worn at the hip yielded the best predictive model. We conclude that in both men and women, cell phone derived activity counts strongly correlate with treadmill gait speed over a wide range of subject ages and weights.

Voluntary changes in step width and step length during human walking affect dynamic margins of stability - Corrected Proof

Patricia M. McAndrew Young, Jonathan B. Dingwell — 2012-04-03

Highlights: ► We quantify how step characteristics influence margins of stability during walking. ► Step length manipulations affect anterior but not lateral stability margins. ► Walking with wider or longer steps increased margin of stability variability. ► Short-term adoption of wider steps may increase instantaneous lateral stability.Abstract: “Cautious” gait is generally characterized by wider and shorter steps. However, we do not clearly understand the relationship between step characteristics and individuals’ stability. Here, we examined the effects of voluntarily altering step width (SW) and step length (SL) on individuals’ margins of stability. Fourteen participants completed three 3-min treadmill walking trials during three SL (short, normal with metronome, and long) and three SW (narrow, normal and wide) manipulation conditions. SL manipulations yielded significant changes in mean anterior–posterior (AP) margins of stability (MOSap) (p<0.0005) but not mediolateral (ML) margins of stability (MOSml) (p≥0.0579). Taking wider steps increased mean MOSml while decreasing MOSap (p<0.0005). Walking with either wider or long steps, each of which increases the base of support, yielded increased AP and ML MOS variability (p≤0.0468). Step-to-step analysis of MOSml indicated that subjects took stable steps followed immediately by stable steps. Overall, short-term, voluntary adoption of wider steps may help increase instantaneous lateral stability but shorter steps did not change lateral stability during unperturbed walking. We suggest that the observed changes in stability margins be considered in gait training programs which recommend short-term changes in step characteristics to improve stability.