Effects of Chair Rise Strategies on Joint Loads

The ability to rise from a sitting position is considered as a key determinant of independence. An ergonomic analysis of sit-to-stand (STS) is needed for people to improve the daily activity, avoid the re-injury and be a reference by documenting the influences on human musculoskeletal system. The goal is to investigate the effects of arm postures and leg positions on joint motion and joint loads during sit to stand period. The twelve young college students without any musculoskeletal disorder were recruited. Three contexts of the sit-to-stand experiment were a normal sit posture with 90 degree of knee joint (N), a normal sit with feet backward 10 cm from sitting with 90 degree of knee joint (FB) and a normal sit posture with arms forward (AF). The height of the chair was adjusted with their leg length from ground to knee joint. The six-camera motion analysis capture system with two force plates were used to collect the segmental movement and ground reaction force. The movement time, kinematics and kinetics of joint were then analyzed. The results were found the range of motion of the hip, knee and ankle were significantly affected by chair raising strategies (p<0.05). FB groups had lower peak moments of the hip than N and AF groups. The largest peak knee moment occurred in FB groups. The peak knee moments among three groups are significantly different (p<0.05). The results of this research would be a reference for strategy use for older people or people who are difficult to rise from sit.