Biomechanical analysis of sit-to-stand transfer in healthy and paraplegic subjects

Objective. An experimental study of the sit-to-stand transfer in healthy ad ults with/without arm-support and in paraplegic patients with/without elect rical stimulation of the quadriceps muscles was performed. The study was ai med to compare the joint torques, momentum transfer hypothesis, and stabili ty of the sit-to-stand transfer in the healthy and paraplegic subjects. Methods. A planar 3-linkage rigid body model was used to compute the body-s egmental linear momentum and the reaction forces and torques at the joints from measured data. Results. In healthy subjects the arm-support enlarged the support base of t he body and thus, increased the postural stability. Strong arm-assistance r educed the maximum hip and knee joint torques by more than 50%. It was obse rved that the healthy participants rising with arm-support used momentum tr ansfer to facilitate the transition from sitting to standing. The paraplegi c participants did not apply the momentum transfer strategy and the sit-to- stand transfer was accomplished in a quasi-static manner. Stimulating the q uadriceps, the legs could participate partly in the movement dynamics. Conclusion. Our results indicate that some significant differences exist be tween the maneuver applied by the paraplegic patients to stand up and the s trategies used by the healthy adults rising with arm-support.