Abstract
Objective: The purpose of this study is to provide a guide for the seat back design by studying the effects of seat back angle on muscle activity and subjective physical comfort in rehabilitation equipment for the aged. Background: While there is a lot of research on rehabilitation equipment for the elderly, there is a lack of research on chair design suitable for rehabilitation equipment. However, rehabilitation requires a chair to support the user's body, while the chair of the rehabilitation device determines his or her posture and has a significant impact on the effectiveness of the exercise and user satisfaction. The backrest angle of chair is an important factor in determining the posture, efficiency, and physical comfort while exercising rehabilitation. Method: In order to study the effect of the seat back angle on muscle activity and physical comfort in the adduction and abduction rehabilitation exercise of the aged, this study conducted some adduction and abduction movements experiment with 12 people aged 65 or older. EMG signals and subjective comforts were measured under five backrest angle ($90^{\circ}$, $100^{\circ}$, $110^{\circ}$, $120^{\circ}$, and $130^{\circ}$). Results: For the hip adduction movement, the backrest angle of the rehabilitation device did significantly affect the muscle activity of the adductor longus and showed an increased muscle activity as the angle increased. For the abduction movement, the back rest angle had a significant effect on the muscle activity of the tensor fascia latae, and the muscle activity tended to increase as the angle increased. There was no significant impact on the muscle activity of gluteus medius, but muscle activity tended to decrease with increasing angles. The subjective comfort during the adduction and abduction movements was shown to be significantly different with the backrest angle. Subjects felt comfortable with a backrest of $100^{\circ}$ to $120^{\circ}$. Conclusion: This study identified how the backrest angle of chair in hip rehabilitation equipment for the elderly affected muscle activity and subjective comfort. The subjective evaluation of physical comfort was significantly affected by the angle of the backrest. The muscle activity showed significant differences in both adduction and abduction movements (except gluteus medius) and that overall the muscle activity varied with the back rest angle. Application: This study could serve as a basis for designing the seat of hip rehabilitation equipment for adduction and abduction exercise.
