Age-gender difference in the biomechanical features of sit-to-stand movement

The purpose of this study was to investigate the effects of age and gender on the biomechanical features of sit-to-stand (STS) movement. Twenty young subjects and 20 elderly subjects participated in this study. Nine events during STS movement were defined where joint angles and joint moments were extracted for further analyses. Two-way repeated measures ANOVA was performed for joint angles and joint moments with age and gender as independent factors. Major gender differences were shown in joint angles. Women used a sliding forward strategy more than men (more flexion of ankle and knee joint) during mid-phases of STS movement (p<0.01) and men used an exaggerated trunk flexion strategy more than women (more hip flexion) in later phases of STS movement (p<0.01). Age differences were shown in joint moments. Elderly subjects showed smaller knee extension moment (normalized by body weight) but greater ankle plantar flexion moment than young subjects in mid-to-late phases of STS movement (p<0.001). More anterior positioning of center of mass (COM) in the elderly might be the reason for the strategy difference. That is, the shorter distance of COM from the knee joint would require less knee extension moment, and likewise, the more forward displacement of COM with respect to the ankle joint would need more plantar flexion moment. More anterior positioning of COM in the elderly, compared to the young was reflected on center of pressure (COP), and the forward displacement of COP was correlated well with the higher body mass index (BMI) and shorter thigh length (r=0.359-0.66;p<0.01).