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Comparisons of Human Balance Control Strategy and Dynamic Stability Between Over-Ground and Treadmill Walking at Different Speeds
balance control,coordination,dynamic stability,COM-COP inclination,continuous relative phase,deviation of phase angle,maximal Lyapunov exponent,
|Publication Year :||2016|
There has been a general awareness that aging comes with increased risk of falling, induced by a poor balance and consequently mobility restrictions. Human walking requires minimal higher-level cognitive input but multi-level physiological sub-systems to maintain dynamic balance, suggested by an integrative control that an active control in the frontal plane but passive control in the sagittal plane. A preferred walking speed (PWS) is then reflected in one’s ability coordinate these sub-systems. For people who have less ability to maintain such a dynamic stability, treadmill-based trainings are usually recommended in clinical settings. However, there has not been a consensus over the differences in the balance control between treadmill walking (TW) and over-ground walking (OW). While a reduction of one’s PWS has been shown to correlate an increasing risk of fall in the elderly, speed effects on the body balance control remains still unclear.
Describing the position and velocity of the body’s center of mass (COM) with respect to the center of pressure (COP), in terms of COM-COP inclination angles (IAs) and their rate of change (RCIA), provides useful information to investigate dynamic balance control during movements. Such balance control is quite complex underlying, which was regarded as a dynamic system. Inter-segment coordination was usually addressed by continous relative phase angle (CRP) determined by two phase plots of the targets in a dynamic system. The control stability in such dynamic system was frequently assessed by variability-based measurements, i.e., deviation of the phase angle (DP), and the maximum Lyapunov exponent (λ_s). Therefore, the purposes of the current dissertation were to compare the similarities and differences in balance control between TW and OW; to investigate the speed effects on the body balance control strategies during TW and OW, in terms of IA/RCIA related variables; to investigate the speed effects on the body balance coordination and dynamic stability in controlling sagittal and frontal COM motion relative to the COP both during TW and OW, in terms of deviation of continuous relative phase angle (CRP), deviation of phase angle (DP) and short-time maximal Lyapunov exponents (λ_s).
Kinematics of the COM and COP in fifteen healthy adults at five belt speeds and three gait speeds, including the subjects’ PWS, was determined using a motion capture system, an instrumented treadmill and forceplates. The current findings suggested that human adapted similar dynamic postural control both during TW and OW, as indicated by the comparable patterns in the balance control of the COM motion relative to the COP. The similarity was also addressed in the coordination between frontal and sagittal COM motion relative to the COP, similar CRP curves were observed regardless of walking speed both for TW and OW. Despite these similarities, when compared to OW, a positive control in the sagittal IA at heel-strike and an active control in the frontal RCIA at toe-off were shown during TW. By adapting the control strategies, PWS appeared to be the best compromise between frontal stability during single-limb support and smooth weight-transfer during double-limb support. As a result of such compromise control, highest dynamic stability was found when subjects walked at their PWS both for TW and OW. These findings might help to explain that why PWS is regarded as a well-recognized locomotor that minimizes the energy expenditure. As the speed effects on the balance control and dynamic stability revealed in the current dissertation, selection of training speeds might be subject to the needs for the target population in the rehabilitation protocol. Nonetheless, 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 to real life over-ground walking.
|Appears in Collections:||醫學工程學研究所|
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