Effects of the type and direction of support surface perturbation on postural responses.
BACKGROUND
Postural control is organized around a task goal. The two most frequently used types of tasks for postural control research are translational (translation along the anterior-posterior axis) and rotational (rotation in sagittal plane) surface perturbations. These types of perturbations rotate the ankle joint, causing different magnitudes and directions of body sway. The purpose of this study was to investigate the effects of the type (translation vs. rotation) and direction (forward/toe up vs. backward/toe down) of the perturbation on postural responses.


METHODS
Nineteen healthy subjects were tested with four perturbations, i.e., forward and backward translation and toe up and toe down rotation. The onset latency and magnitude of muscle activations, angular changes, and COM displacements were measured. In addition, the kinematic data were divided into two phases. The initial phase reflected the balance disturbance induced by the platform movement, and the reversal phase reflected the balance reaction.


RESULTS
The results showed that, in the initial phase, rotational perturbation induced earlier ankle movement and faster and larger vertical COM displacement, while translational and forward/toe up perturbations induced larger head and trunk angular change and faster and larger horizontal COM displacement. In the reversal phase, balance reaction was attained by multi-joint movements. Translational and forward/toe up perturbations that induced larger upper body instability evoked faster muscle activation as well as faster and larger hip or knee joint movements.


CONCLUSIONS
These findings provide insights into an appropriate support surface perturbation for the evaluation and training of balance.
Chiung-Ling
CL
Chen
Shu-Zon
SZ
Lou
Hong-Wen
HW
Wu
Shyi-Kuen
SK
Wu
Kwok-Tak
KT
Yeung
Institute of Biomedical Engineering, National Cheng Kung University, 1 University Rd,, Tainan 701, Taiwan. fcsu@mail.ncku.edu.tw.
Fong-Chin
FC
Su
D001696:Biomechanical Phenomena / Q000502:physiology; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D004856:Postural Balance / Q000502:physiology*; D011434:Proprioception / Q000502:physiology*; D055815:Young Adult