Gait & Posture - Articles in Press

Further evidence of validity of the Gait Deviation Index - Corrected Proof

M. Molloy, B.C. McDowell, C. Kerr, A.P. Cosgrove — 2010-03-12

Abstract: In this paper, the relationship of the Gait Deviation Index (GDI) to gross motor function and its ability to distinguish between different Gross Motor Function Classification System (GMFCS) levels was determined. A representative sample of 184 ambulant children with CP in GMFCS levels I (n=57), II (n=91), III (n=22) and IV (n=14) were recruited as part of a population-based study. Representative gait cycles were selected following a 3D gait analysis and gross motor function was assessed using the Gross Motor Function Measure (GMFM). GDI scores were calculated in Matlab. Valid 3D kinematic data were obtained for 173 participants and both kinematic and GMFM data were obtained for 150 participants. A substantial relationship between mean GDI and GMFM-66 scores was demonstrated (r=0.70; p<0.001) with significant differences in mean GDI scores between GMFCS levels (p<0.001) indicating increasing levels of gait deviation in subjects less functionally able. The relationship between the GDI, GMFM and GMFCS in a representative sample of ambulators, lends further weight to the validity of the GDI scoring system. Furthermore it suggests that the subtleties of gait may not be wholly accounted for by gross motor function evaluation alone. Gait specific tools such as the GDI more likely capture both the functional and aesthetic components of walking.

Postural instability in Charcot-Marie-Tooth type 1A patients is strongly associated with reduced somatosensation - Corrected Proof

2010-03-12

Abstract: In order to determine the influence of somatosensory impairments, due to the loss of large myelinated fibres, on the postural stability of Charcot-Marie-Tooth 1A (CMT) patients, a cross-sectional balance assessment was done. Nine CMT patients were compared with eight patients with a distal type of Spinal Muscular Atrophy (SMA), and 11 healthy control subjects. The balance assessment consisted of four tasks: quiet barefoot standing on a stable versus compliant surface, with eyes opened or closed. Force plate signals were used to calculate the velocity of the centre of pressure of the ground reaction forces. The patients’ distal muscle force (MRC scale), vibration detection threshold (Rydel-Seiffer tuning fork) and superficial tactile sensation (Semmes-Weinstein monofilaments) were clinically assessed. Compared to the healthy subjects, postural stability of both patient groups was seriously impaired, however, increased visual dependency was only found in the CMT patients. The postural instability of the CMT patients correlated significantly with decreased vibration sense only. The strength of the correlation increased with task complexity. It is concluded that somatosensory deficits substantially contribute to impaired postural stability and increased visual dependency in CMT patients.

Multiple Sclerosis Walking Scale-12 and oxygen cost of walking - Corrected Proof

2010-03-12

Abstract: Background: The 12-item multiple sclerosis walking scale (MSWS-12) has been validated against self-report and clinical markers, but has not been validated with a physiological marker of locomotor impairment.Objective: This study further validates the MSWS-12 based on its correlation with the oxygen cost (O2 cost) of walking as a physiological marker of locomotor impairment in persons with multiple sclerosis (MS).Methods: Participants (N=24) with MS completed the MSWS-12 and then wore a portable metabolic unit for measuring the O2 cost of walking during three 6-min walk (6MW) tests. The first 6MW test involved the participant's comfortable walking speed (CWS), whereas the second and third 6MW tests were undertaken above (faster walking speed, FWS) and below (slower walking speed, SWS) the participant's CWS (i.e., ±5mph CWS).Results: MSWS-12 scores correlated strongly with O2 cost of walking during the 6MW tests undertaken at CWS (r=.641, p=.001), FWS (r=.616, p=.001), and SWS (r=.639, p=.001).Interpretation: We provide evidence that further confirms the validity of the MSWS-12 as a measure of the impact of MS on walking.

Overground vs. treadmill walk-to-run transition - Corrected Proof

I. Van Caekenberghe, K. De Smet, V. Segers, D. De Clercq — 2010-03-11

Abstract: Determination of the walk-to-run transition (WRT) speed is a crucial aspect of gait transition research, which has been conducted on treadmill as well as overground. Overground WRT-speeds were reported to be higher than on treadmill.Part of this difference could be related to the lower acceleration magnitudes on treadmill. In this study, spontaneous WRT overground was compared to WRT at a comparable acceleration on treadmill. In addition, calculation procedures correcting for movement in the lab reference frame on treadmill were implemented. As such, this study was, in contrast to previous treadmill studies, able to detect a speed jump. This speed jump was until now a typical feature of overground WRT and contributed to the higher transition speed.By incorporating horizontal movements of the COM, a speed jump was also detected on treadmill. Yet, treadmill WRT-speed (2.61ms−1) remained lower than overground (2.85ms−1). Nevertheless, this difference was much smaller than assumed in the literature. The remaining difference could be explained by a larger speed jump (treadmill: 0.40ms−1; overground: 0.51ms−1), and a higher speed at the start of the transition step overground (treadmill: 2.21ms−1; overground: 2.34ms−1).In conclusion, even when controlling for effects of acceleration and movement in the lab reference frame a treadmill influence on WRT was visible.

Three-dimensional ankle kinematics and kinetics during running in women - Corrected Proof

2010-03-11

Abstract: Stress fractures are common in athletics and are more prevalent in women. The current literature has not identified a reason for this gender difference. We hypothesized that females with a history of a second/third metatarsal stress fracture will demonstrate differences in ankle kinematics, kinetics and ground reaction forces when compared with a group of age-matched females with no stress fracture history. A total of 15 control females and nine females with a history of a second/third metatarsal stress fracture were asked to run at 3.3m/s±5% along a 10-m runway. Kinematics and kinetics were obtained using an 8-camera motion analysis system (240Hz) and two force plates (1200Hz).Significant differences existed in height and weight between the groups. No other statistically significant differences existed between the fracture group and the control group. Kinematic measurements do not differ significantly between women with a history of second/third metatarsal stress fracture and female control subjects. The reported kinematic and kinetic measurements do not appear to be influenced in subjects with metatarsal stress fractures, which likely result from the complex relationships between the joints in the foot and ankle. The development of second/third metatarsal stress fractures could result more from over training or changes in plantar loading instead of changes in lower extremity joint kinematics while running.

Balance is impaired in people with chronic obstructive pulmonary disease - Corrected Proof

2010-03-08

Abstract: Background: It has recently been suggested that people with chronic obstructive pulmonary disease have an increased risk of falls. Although falls risk is multifactorial, impaired balance may contribute. The primary aim of this study was to compare balance between people with and without chronic obstructive pulmonary disease and the secondary aim was to determine if balance deteriorates when respiratory demand is increased by upper limb exercise.Methods: Twelve people with chronic obstructive pulmonary disease and 12 healthy control subjects participated in this study. Participants stood on a force plate to record centre of pressure displacement during a range of conditions that challenge balance. Lumbar spine and hip motion were measured with inclinometers. Balance trials were performed before and after participation in upper limb exercise that increased respiratory demand in those with chronic obstructive pulmonary disease.Findings: People with chronic obstructive pulmonary disease had increased mediolateral centre of pressure displacement and increased angular motion of the hip compared to healthy controls. Mediolateral centre of pressure displacement was further increased in people with chronic obstructive pulmonary disease following exercise, but unchanged in controls. Anteroposterior centre of pressure displacement did not differ between groups.Interpretation: People with chronic obstructive pulmonary disease have reduced control of balance in the mediolateral direction. This may contribute to an increased risk of falls in this population.

Corrected Proof

James Robb — 2010-03-08

This is an excellent book. Firstly it builds on the strengths of the first edition and secondly it is a tribute to Dr James Gage's efforts to improve the understanding and management of patients with cerebral palsy (CP). Since the first edition six years ago there has been an increase in the number of gait laboratories and a burgeoning number of publications in the field of motor impairment. This is reflected in the enlargement of that first edition (448 pages, one DVD and one editor) to 664 pages, two DVDs and four editors in the present edition.

Trunk sway reductions in young and older adults using multi-modal biofeedback - Corrected Proof

2010-03-08

Abstract: This study investigated whether real-time biofeedback of angular trunk displacement could alter balance performance among healthy older and young adults. Healthy community-dwelling older adults (n=32) and healthy young adults (n=32) were included in the randomized control trial study. The intervention group received combined vibrotactile, auditory and visual biofeedback of angular trunk displacement in real-time during training on a battery of static and dynamic balance tasks and during the subsequent post-training balance re-assessment. The control group received balance training and were re-assessed in the absence of real-time biofeedback of their trunk displacement. The 90% range of angular trunk displacement was calculated for each balance task pre- and post-training. Significant age-related differences were observed independent of the intervention. Biofeedback intervention significantly changed the angular displacement of the trunk for both young and older participants on a number of balance tasks compared to control treatment (40–60% reduction in angular displacement). In some cases, biofeedback influenced balance in older adults, but not younger adults.

Correlations of the Gait Profile Score and the Movement Analysis Profile relative to clinical judgments - Corrected Proof

Sarah Beynon, Jennifer L. McGinley, Fiona Dobson, Richard Baker — 2010-03-04

Abstract: The Gait Profile Score (GPS) is a single index measure that summarises the overall deviation of kinematic gait data relative to normative data. The GPS can be decomposed to provide Gait Variable Scores (GVS) of nine key component kinematic gait variables, which are presented as a Movement Analysis Profile (MAP). The purpose of this study was to investigate the validity of the GPS and MAP relative to clinician judgments.Kinematic data were selected from 60 children and inspected by 17 experienced clinicians. The degree of abnormality of the overall unilateral gait pattern and the nine kinematic variables was rated according to a 0–10 point scale.Strong, significant, positive correlations were found between the GPS and MAP component scores, and clinicians’ ratings of kinematic gait deviation, with Spearman correlations ranging from 0.84 to 0.97. These high correlations provide evidence that the GPS and the MAP have criterion-related validity relative to clinician judgments. We propose that the GPS and particularly its MAP decomposition may be useful in clinical practice and education as an adjunct to the traditional presentation of complex kinematic data.

Effects of virtual reality training on gait biomechanics of individuals post-stroke - Corrected Proof

Anat Mirelman, Benjamin L. Patritti, Paolo Bonato, Judith E. Deutsch — 2010-03-02

Abstract: Objective: To evaluate gait biomechanics after training with a virtual reality (VR) system and to elucidate underlying mechanisms that contributed to the observed functional improvement in gait speed and distance.Design: A single blind randomized control study.Setting: Gait analysis laboratory in a rehabilitation hospital and the community.Participants: Fifteen men and three women with hemiparesis caused by stroke.Interventions: Subjects trained on a six-degree of freedom force-feedback robot interfaced with a VR simulation. Subjects were randomized to either a VR group (n=9) or non-VR group (NVR, n=9). Training was performed three times a week for 4 weeks for approximately 1h each visit.Main outcome measures: Kinematic and kinetic gait parameters.Results: Subjects in the VR group demonstrated a significantly larger increase in ankle power generation at push-off as a result of training (p=0.036). The VR group had greater change in ankle ROM post-training (19.5%) as compared to the NVR group (3.3%). Significant differences were found in knee ROM on the affected side during stance and swing, with greater change in the VR group. No significant changes were observed in kinematics or kinetics of the hip post-training.Conclusions: These findings are encouraging because they support the potential for recovery of force and power of the lower extremity for individuals with chronic hemiparesis. It is likely that the effects of training included improved motor control at the ankle, which enabled the cascade of changes that produced the functional improvements seen after training.

Medio-lateral stability of sit-to-walk performance in older individuals with and without fear of falling - Corrected Proof

Anna Cristina Åberg, Gunilla Elmgren Frykberg, Kjartan Halvorsen — 2010-03-02

Abstract: Most falls in older people are due to loss of balance during everyday locomotion, e.g., when initiating walking from sitting; sit-to-walk (STW). It has been considered that the broader stride width in walking that is seen in many people with fear of falling (FoF) does not increase stability, but could be predictive of future falls because of increased medio-lateral (ML) velocity of the body centre of mass (CoM). This study was aimed to examine step-, velocity- and stability-related parameters, focusing on ML stability, in STW performance of people with and without FoF. Ten subjects with FoF and 10 matched controls, aged ≥70 years, were included. Kinematic and kinetic data were collected in a laboratory. Stability parameters were calculated from a formula implying that the vertical projection of the CoM extrapolated by adding its velocity times a factor √l/g (height of inverted pendulum divided by gravity) should fall within the base of support (BoS). A related spatial margin of stability (SMoS), defined as the minimum distance from the extrapolated CoM (XCoM) to the boundaries of the BoS, was also calculated. In the phase ‘seat-off–second-toe-off’, the FoF group had significantly (p<0.05) shorter and broader steps, lower forward but similar ML CoM velocity, and broader CoM and XCoM widths. The FoF group therefore exhibited a disproportionately large sideways velocity compared to the controls. This indicates that STW may be a hazardous transfer for older people with FoF, which should be relevant in assessment and training aimed at preventing falls.

Utilized friction when entering and exiting a dry and wet bathtub - Corrected Proof

2010-02-26

Abstract: Bathtubs and showers are a common source of unintentional slips and falls. The goal of this study was to quantify the friction used by barefoot subjects entering and exiting a typical bathtub/shower enclosure under dry and wet conditions. Sixty subjects (30F, 30M) from three age groups (20–30 years, 40–50 years, 60–70 years) entered and exited a slip-resistant bathtub using six movement patterns (three entering and three exiting the tub) simulating actual use. Force plates installed in the tub floor and the slip-resistant deck outside the tub measured ground reaction forces, from which utilized friction and double support times were calculated. Overall, utilized friction varied from 0.102 to 0.442 (0.235±0.057) and was 0.058±0.040 lower in wet than dry conditions across all movement patterns (p<0.0001). During tub exiting movements, older subjects used less friction than young subjects (p<0.006). Utilized friction did not vary between genders (p>0.14). Double support times were longer in older subjects than in both young and middle-aged subjects for all movement patterns (p<0.0009) and longer under wet than dry conditions for all entry movements (p<0.0001). These data suggest that subjects regard the wet condition as more hazardous than the dry condition and adapt their utilized friction accordingly. These data also show that older subjects are more cautious than young subjects when confronted with the dual tasks of stepping over the tub's apron and transitioning to a surface perceived to be more slippery.

Variation in trunk kinematics influences variation in step width during treadmill walking by older and younger adults - Corrected Proof

Christopher P. Hurt, Noah Rosenblatt, Jeremy R. Crenshaw, Mark D. Grabiner — 2010-02-25

Abstract: Step-by-step variations in step width have been hypothesized to reflect adjustments to swing foot placement in response to preceding frontal plane trunk kinematics. The present study tested this hypothesis while 12 younger and 11 older subjects walked on treadmill for 10min at a self-selected velocity. The relationship between step-by-step variations in step width and frontal plane trunk COM kinematics was determined using multiple regression analysis. Trunk kinematics at midstance were significantly (p<0.001) and strongly (R2=0.54) related to the subsequent foot placement supporting the primary hypothesis. Additionally, this relationship was significantly affected by age (p<0.001) and stepping limb (p<0.001). These results implicate feedback driven control of foot trajectory during the swing phase. Further, they provide a biomechanical framework by which loss of frontal plane dynamic stability may result from a step width that is insufficient to decelerate and redirect trunk kinematics in preparation for the next step.

Kinematic analysis of side-by-side stepping with intentional and unintentional synchronization - Corrected Proof

Jeff A. Nessler, Sara J. Gilliland — 2010-02-24

Abstract: Interpersonal synchronization of stepping during side-by-side walking may assist in the rehabilitation of gait for mildly impaired individuals. However, little is known regarding the effects of step synchronization on lower limb movement kinematics. The purpose of this study was to compare normal treadmill walking to walking under conditions of intentional and unintentional synchronization of stepping. Twenty pairs of subjects walked on side-by-side treadmills independently, paired (side-by-side under conditions in which unintentional synchronization was likely to occur), and paired with forced synchronization (instructed to purposely synchronize stepping). Of these 20 pairs, six pairs (12 individuals) demonstrated unintentional synchronization for over 99% of the paired walking trial. An optical motion capture system was used to compare lower limb kinematics for each of the three walking conditions in these six pairs. The data indicated that forced synchronization of stepping resulted in steps that were significantly smaller and faster when compared to independent and unintentional synchronization conditions. In addition, stride time standard deviation was reduced for both the intentional and unintentional synchronization conditions, but these reductions were not significant. No differences were noted between the unintentional synchronization and independent walking conditions. These results suggest that unintentional synchronization might be preferable to intentional synchronization for gait rehabilitation in certain individuals. Additional work is necessary to understand the effects of side-by-side walking and its potential for use in a therapeutic setting.

Alternative modelling procedures for pelvic marker occlusion during motion analysis - Corrected Proof

Jodie A. McClelland, Kate E. Webster, Cameron Grant, Julian Feller — 2010-02-22

Abstract: Background: Motion analysis of participants with different body shapes under diverse conditions can be problematic when vital markers are occluded. The markers located over the anterior superior iliac spines are commonly occluded in older patients and during analysis of activities with trunk and hip flexion which can prevent accurate calculation of lower limb joint kinematics. Options to modify standard body models exist but have not been described in detail, and the effects on the lower limb kinematics are not known.Methods: Three-dimensional motion analysis data were collected from 10 participants during level walking. A single trial from each participant was processed using the standard PlugIn Gait model and with four alternative modelling procedures where either one or both anterior pelvis markers were not labelled for all or part of the trial. Similarity of these alternative procedures to PlugIn Gait was assessed by comparison of peak kinematic characteristics and Root Mean Square (RMS) across the gait cycle.Findings: The peak lower limb kinematics of all four alternative modelling procedures were similar to PlugIn Gait to within 4.57°. The alternative procedure most similar to PlugIn Gait was less than 1.24° different. The largest RMS was 2.88° and the smallest was 0.92°.Interpretation: This study has presented several options for researchers and clinicians to modify the standard body models of motion analysis so that lower limb kinematics may be calculated without reliance on continuous visualisation of anterior pelvic markers. Although the alternative modelling processes are subject to different sources of error which need to be considered, the error is minimal.

The effects of stride length and stride frequency on trunk coordination in human walking - Corrected Proof

2010-02-22

Abstract: In speeding-up normal walking, relative phase between horizontal thorax and pelvis rotations changes from more in-phase (synchronous) to more out-of-phase. In pathology (stroke, Parkinson's disease, low-back pain, pregnancy-related pelvic girdle pain), this often fails to happen. Even in healthy gait, however, these phenomena remain poorly understood. Thorax–pelvis relative phase may increase with either stride length, or stride frequency. Sixteen healthy male subjects walked on a treadmill at 0.5m/s, 1.0m/s, or 1.5m/s, with small, normal, or large steps. Increasing stride length (with lower frequency) led to larger spinal rotations, larger thorax–pelvis relative phase, and lower pelvis–leg relative phase, while the thorax continued to counterrotate with respect to the leg. With small steps, speeding-up hardly affected thorax–pelvis relative phase, and spinal amplitudes remained low. From a certain walking speed onwards, pelvis rotations start to contribute to stride length, and thus to speed (the “pelvic step”). This phenomenon appears to be driven, and the present study suggests, at least for higher speeds, that also thoracic counterrotations are driven, and not determined by the passive dynamics of the system. For patients, several strategies may exist to avoid large thorax–pelvis relative phase, and the concomitant large rotations of the spine: walking slowly, walking with small steps, adapting the timing of thorax rotations to that of the pelvis, or refraining from adapting the timing of pelvis rotations to the movements of the leg.

Kinematic differences between normal and low arched feet in children using the Heidelberg foot measurement method - Corrected Proof

D. Twomey, A.S. McIntosh, J. Simon, K. Lowe, S.I. Wolf — 2010-02-22

Abstract: The purpose of this study was to investigate the kinematics of normal arched and low arched feet in children and use this data to quantify the differences between the two foot types during walking gait. Multi-segment foot motion was measured, using the Heidelberg foot measurement method (HFMM), for 25 normal arched feet and 27 low arched feet in 9–12-year-old children. The kinematic differences in the foot between the two groups during walking were relatively small, except for the medial arch and forefoot supination angles. The magnitude of the medial arch angle was approximately 10° greater in the low arched group than the normal arched group throughout the gait cycle. There was a significant difference found in the forefoot supination angle (p<0.03), relative to the midfoot, between the two groups at initial heel strike, and maximum and minimum values throughout the gait cycle. The values for the normal group were significantly higher in all these angles indicating that the forefoot of the low arched foot remains less pronated during the gait cycle. There was no significant difference in the motion of the rearfoot between the two foot types. The results of this study provide normative values for children's feet and highlight the mechanical differences in flexible flat feet in this age group. This data contributes to knowledge on foot kinematics in children and will be valuable for future research on the structure, function and potential treatment of the flexible flat foot.

Validation of 3-D freehand ultrasound for the determination of the hip joint centre - Corrected Proof

Alana Peters, Richard Baker, Morgan Sangeux — 2010-02-19

Abstract: This paper describes the calibration process for 3-D free hand ultrasound (3-DUS). The Cambridge calibration technique was determined to produce the most repeatable and accurate results when determining the location of a reference object within a water bath. This note additionally validates 3-DUS as a potential measurement tool for the determination of the hip joint centre. It shows that 3-DUS can accurately determine the inter-HJC distance to within 4±2mm. This indicates potential for 3-DUS to be used as a gold standard measurement tool in the identification of the hip joint centre.

Using ambulatory virtual environments for the assessment of functional gait impairment: A proof-of-concept study - Corrected Proof

Martin Gérin-Lajoie, Deborah McK. Ciombor, William H. Warren, Roy K. Aaron — 2010-02-19

Abstract: This study aimed to demonstrate the sensitivity of virtual reality (VR)/motion tracking to detect global functional gait impairment resulting from an emulated knee disability as a prelude to describing mobility changes following lower limb injury/treatment. Participants walked in a figure-8 around two virtual posts placed 6m apart while viewing the computer-generated environment in a helmet-mounted display. Three-dimensional position and orientation of the participant's head were tracked and used to update the virtual scenes, measure walking path and speed, and control task parameters with real-time feedback. Participants walked with/without an emulated lower extremity disability (splint preventing normal knee flexion). Participants performed the task at self-selected Natural (NAT) speed providing a baseline measure of their turning speed and area. Turning speed and area were then in turn maintained fixed (controlled speed, CS; controlled path, CP) while the other variable was measured as a gait impairment indicator. Different adaptive strategies were used to cope with the emulated deficit during the NAT scenario: maintaining turning speed while altering path geometry; decreasing turning speed while maintaining path geometry; and combining the previous two strategies. This resulted, on average, in decreased turning speeds and increased turning areas. The CS and CP manipulations respectively generated even greater turning areas and more consistent speed decreases. The three subtests acted as intertwined filters enabling the detection of functional gait impairment in all subjects regardless of their adaptive strategies. This proof-of-concept study demonstrated how VR/motion tracking technology can be used to detect and quantitatively characterize global functional mobility impairment.

Head stabilization in children of both genders during level walking - Corrected Proof

Claudia Mazzà, Mounir Zok, Aurelio Cappozzo — 2010-02-17

Abstract: Young healthy adults adopt a “head stabilization in space” strategy during walking by attenuating the acceleration going up from pelvis-to-head level. A gender difference exists in this control strategy, particularly evident in the control of medio-lateral dynamic equilibrium. This study aims at assessing whether this difference is already present at pre-pubertal age.Two groups of children (15 females and 15 males, age range: 8–11 years) were involved in the study. They were asked to walk at self-selected speed and movement data were collected using three inertial sensors firmly attached at pelvis (P), shoulder (S), and head (H) levels. The RMS of the accelerations of P, S, and H were computed along the antero-posterior (AP), medio-lateral (ML), and vertical (V) directions and used to compare the two groups.No differences were found between the two groups in the pelvis and shoulder acceleration RMS values. Conversely, lower head acceleration RMS values were found for the females in both the AP and ML directions. Both groups managed to attenuate the upper body AP and ML accelerations going from pelvis-to-head level, with higher attenuations found for the females.The results of this study suggest that the gender differences in the ability to control the head accelerations during gait, found in a previous study, are due neither to different mass distribution nor to a compensation of the greater pelvic motions, nor are they the result of gender related walking habits (e.g. use of high heels).

Non-linear dynamical features of center of pressure extracted by recurrence quantification analysis in people with unilateral anterior cruciate ligament injury - Corrected Proof

2010-02-17

Abstract: Knowledge about the non-linear dynamical pattern of postural sway may provide important insights into the adaptability (flexibility) of human postural control in response to everyday stresses imposed on the body. A commonly used non-linear tool, i.e. recurrence quantification analysis, was chosen to investigate the effect of prior anterior cruciate ligament injury on the deterministic pattern of postural sway under different conditions of postural and cognitive difficulty. In double leg stance, as postural difficulty increased from open-eyes to closed-eyes and rigid-surface to foam-surface, the centre of pressure regularity (%determinism) increased as well. In comparison to healthy counterparts, subjects with prior anterior cruciate ligament injury produced more regularity when maintaining balance on their injured leg. Also, for both the double and single leg stance balance conditions, the performance of a secondary cognitive task (a backward digit span task) caused less center of pressure regularity than the single postural task, which suggests that both study populations required the same amount of cognitive involvement for maintaining balance. Center of pressure dynamic patterns exhibited by the anterior cruciate ligament deficient patients were more regular than those of the healthy controls indicating “complexity loss” and may be indicative of the reduced adaptability (flexibility) of a balance system to sudden perturbations.