Effect of trunk angle on lower limb joint moment in different strategies of sit-to-stand-to-sit motion with healthy subjects

Abstract

Patients with lower limb impairments often face sit-to-stand-to-sit motion challenges. The patients utilize a greater trunk flexion angle at seat-off time to mitigate knee moment. Alternative methods of STSTS motion strategies are required to study and understand the various patterns to guide physical rehabilitation programs in clinical practice. Four different STSTS strategies—Natural, Full Flexion, Pelvis-spine alignment, and Frame-Assisted—were experimented with twenty healthy subjects in a 3D motion capture lab, and inverse kinematics and dynamics methods were used for motion analysis in Visual 3D. At seat-off time in full flexion, the maximum trunk flexion angle is 58.77(± 17.92) degrees, duration is 1.63 s, 27% of the cycle, which reduces knee moment by -0.466(± 0.2) N.m/kg, increased hip moment by 0.67(± 0.312) N.m/kg, and ankle moment by 0.225(± 0.09) N.m/kg for the compensation. The compensatory movement also occurred while sitting down. Frame-assisted STSTS motion reduced knee moments without increases in hip and ankle moments at the maximum of trunk flexion angle while standing and sitting, and its motion patterns are similar to pelvis-spine alignment and natural strategies. These findings provide valuable insights for physiotherapists to predict the current stage of the patient for clinical assessment and guide in the design and development of medical devices. © International Federation for Medical and Biological Engineering 2025.