Elsevier

Gait & Posture

Volume 53, March 2017, Pages 248-253
Gait & Posture

Full length article
Comparison of body’s center of mass motion relative to center of pressure between treadmill and over-ground walking

https://doi.org/10.1016/j.gaitpost.2017.02.003Get rights and content

Highlights

  • Both OW and TW showed COM/COP movement in similar butterfly patterns.

  • OW and TW maintained dynamic balance with similar patterns of COM/COP movement.

  • Differences in COM/COP motion between TW and OW were revealed by IAs and RCIAs.

  • Rolling belt affected the COM/COP control both in the sagittal and frontal plane.

Abstract

Treadmills have been used in rehabilitation settings to provide convenient protocols and continuous monitoring of movement over multiple cycles at well-controlled speeds for gait and balance training. However, the potential differences in the movement control may affect the translation of the training outcomes to real life over-ground walking (OW). The similarities and differences in the balance control between treadmill walking (TW) and OW have largely been unexplored. The current study bridged the gap by comparing the motions of the body’s center of mass (COM) relative to the center of pressure (COP) between TW and OW, in terms of the COM-COP inclination angle (IA) and its rate of change (RCIA). The movement of the COM and COP separately were quite different between OW and TW, but when describing the COM motion relative to the COP, the COM motions became similar qualitatively with similar butterfly patterns. However, significantly increased peak values in themediolateral RCIA and greater ranges of mediolateral IA were found during TW (p < 0.004). In the sagittal plane, the posterior velocity of the belt led to an anterior RCIA (posterior RCIA in OW) with increasing anterior IA during early double-limb support phase, and reduced posterior RCIA (p < 0.009) with an increased anterior IA (p < 0.001) during the remainder of the phase. These differences between TW and OW may have to be taken into account in future designs of strategies to optimize the translation of treadmill gait training outcomes into real life over-ground walking.

Introduction

Treadmills have played an important role in gait and balance training in rehabilitation settings, providing convenient protocols and enabling continuous monitoring of the movement over multiple gait cycles at well-controlled speeds. Instrumented treadmills further strengthen the clinical applications by enabling measurements of the reaction forces to provide quantitative assessment of gait and balance. Intensive training on the treadmill has been shown to improve gait performance, and thus increase the quality of life in patients with neurological diseases (e.g., [1], [2], [3]). While gait training on treadmills has been successful in the rehabilitation of patients with gait problems [1], [2], [3], there has not been a consensus over the differences in the movement control between treadmill walking (TW) and over-ground walking (OW) (e.g., [4], [5], [6]). A better understanding of such differences would be helpful for translating treadmill training outcomes into real life over-ground walking [5].

Previous studies on the differences between TW and OW have focused mainly on the spatial-temporal parameters, kinematics and/or kinetics of the lower limb joints, muscle activities or inter-limb coordination [4], [5], [6], [7], [8], [9]. Some studies reported that movement patterns during TW are similar to those during OW [7], [9], while others showed different patterns between TW and OW [4], [5], [6], [8]. Since the neuromusculoskeletal system has multiple degrees of freedom, a complete picture of the differences between TW and OW may not be obtained by comparing only some of the individual degrees of freedom. An alternative could be the comparisons of the net effect of the control of these multiple degrees of freedom, e.g., whole body balance control.

During walking, the body’s balance control depends not only on the position, but also on the velocity of the center of mass (COM) relative to a constantly changing and moving base of support or center of pressure (COP) [10], [11], and is different between single- and double-limb support (SLS and DLS) [12]. During OW, the COM and the base of support continue to move forward with respect to the ground, but are fairly stationary relative to the treadmill surface during TW. Compared to OW, TW showed reduced trunk oscillation [13] but wider step width with the same mediolateral stability as indicated by the same minimum margin of stability [14]. Given the different neuromechanical challenges between OW and TW, it seems unlikely that the same level of stability under these two walking conditions would be maintained with the same COM relative to COP movements.

The motion of the COM relative to a global frame of reference or to the COP has been used to quantify the balance control during OW in previous studies [15]. The COM-COP relative motions, described using horizontal COM-COP separations, have also been used to quantify balance control during over-ground walking [16], but ignoring the vertical component of the COM is a limitation of the COM-COP separation that cannot be dealt with by normalizing the separation by leg length or body height [17]. To overcome this limitation and to remove the need for defining a dynamic base of support, COM-COP inclination angles (IAs) defining the orientation of the line connecting the COP and COM, and the rate of change of IA (RCIA), have been used to describe the body’s balance control between groups and between terrain conditions during walking [15], [18], [19]. However, no study has identified the differences in balance control between TW and OW for both sagittal and frontal planes in terms of IA and RCIA.

The purpose of the current study was to compare the motions of the body’s COM relative to the COP between TW and OW in healthy young adults, in terms of the COM-COP inclination angle (IA) and its rate of change (RCIA). It was hypothesized that TW and OW would show different IA and RCIA, both qualitatively and quantitatively, and in both the sagittal and frontal planes.

Section snippets

Subjects

Fifteen young male adults (age: 24.5 ± 2.3 years, height: 172.3 ± 6.3 cm, mass: 68.4 ± 8.3 kg) participated in the current study with written informed consent as approved by the Institutional Research Board. All subjects were free of neuromusculoskeletal dysfunction and had normal or corrected-to-normal vision as quantified by their visual acuity. Each subject wore 39 retroreflective markers to track the motions of the body segments [20].

Data collection

In a gait laboratory, each subject was asked to walk barefoot on

Results

All the derived variables were found to be normally distributed. No significant differences in walking speed, cadence, and normalized step length, step width and maximum M/L excursions of COM were found between OW and TW. However, TW showed significantly greater normalized maximum M/L excursions of COP and a shorter SLS duration (p < 0.001), but with increased DLS and stance phase durations (p < 0.001) (Table 1).

The movement patterns of the COM and COP were quite different between OW and TW (Fig. 1

Discussion

In the laboratory coordinate system, the movement patterns of the COM and COP separately were quite different between OW and TW (Fig. 1a), but when described relative to the COP, both OW and TW showed COM movement in similar butterfly patterns (Fig. 1b). These results suggest that while walking on a moving surface at constant speed, i.e., on a treadmill, the body balance was maintained by dynamic postural control with patterns of the body’s COM movement relative to the COP similar to those

Conclusions

When observed in the laboratory coordinate system, the movement patterns of the COM and COP separately were quite different between OW and TW, but when described relative to the COP, both OW and TW showed COM movement in similar butterfly patterns. These results suggest that while walking on a moving surface translating at constant speed, i.e., TW, the body’s balance was maintained by dynamic postural control with patterns of the body’s COM movement relative to the COP similar to those during

Acknowledgements

The authors are grateful for the financial support from Ministry of Science and Technology of Taiwan, R.O.C. Thanks also to Mr. Ting-Yi Chen for his assistance with the data collection for treadmill walking.

References (30)

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