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 signi®cant dierences exist between the maneuver applied by the paraplegic patients to
stand up and the strategies used by the healthy adults rising with arm-support.