Determination of Optimal Riding Positions using Muscle Co-Contraction on Upper Extremity during Manual Standing Wheelchair Propulsion

A newly designed standing wheelchair that moves even while standing posture has been developed to improve the health and the quality of life for wheelchair users. However, this standing wheelchair has hand rims separate from the wheels, likely affecting the biomechanical characteristics and the efficiency of propulsion. Thus, this study aimed to propose a method to determine the optimal riding position by evaluating muscle activation during manual standing wheelchair propulsion. Ten elderly male subjects were asked to propel the hand rims with nine different seat (while sitting) and footrest (while standing) positions. During the experiments, kinematic data were obtained using a 3D motion capture system and sEMG measurement system, respectively. Simultaneously, surface electromyography signals were recorded from eleven muscles on the right side of the trunk and the upper extremity to evaluate relative iEMG and muscle co-contraction ratio. The muscle co-contraction ratio was higher at positions (upward and backward directions) distant from the hand rim and lower at positions (downward and forward directions) close to the hand rim. These results indicate that decreased distance from the hand rim enhances joint stability and decreases muscle co-contraction. These results also showed a good similarity with our previous study using energy expenditure method.