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

Objective. An experimental study of the sit-to-stand transfer in healthy adults with/without arm-support and in paraplegic patients with/without electrical stimulation of the quadriceps muscles was performed. The study was aimed to compare the joint torques, momentum transfer hypothesis, and stability 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-segmental 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 the body and thus, increased the postural stability. Strong arm-assistance reduced the maximum hip and knee joint torques by more than 50%. It was observed that the healthy participants rising with arm-support used momentum transfer to facilitate the transition from sitting to standing. The paraplegic participants did not apply the momentum transfer strategy and the sit-to-stand transfer was accomplished in a quasi-static manner. Stimulating the quadriceps, the legs could participate partly in the movement dynamics. Conclusion. Our results indicate that some significant differences exist between the maneuver applied by the paraplegic patients to stand up and the strategies used by the healthy adults rising with arm-support.