Model-based control for exoskeletons with series elastic actuators evaluated on sit-to-stand movements.

The study tested 15 non-disabled young adults, not people with muscle weakness or neurologic disorders, so it does not show that the exoskeleton helps patients. The conditions were performed in a fixed order, with the no-exoskeleton condition always first because putting the exoskeleton on took almost half an hour, so order effects cannot be ruled out. The force plate setup prevented self-selected foot placement, and the right leg was placed slightly more outward than normal, although the same position was used in every condition. The assistance torque was precomputed off-line from simulated muscle weakness in a previous study, not generated in real time from each participant's own capability. The hip motor saturated in the assistance condition, so the study could not properly evaluate whether assistance changed effort compared with the compensated condition. Only sit-to-stand was analysed in depth, stand-to-sit was not analysed in depth, and walking was not tested. EMG was not corrected for fatigue between conditions, and no direct comparison with impedance control was made.

Funding was provided by Agentschap voor Innovatie door Wetenschap en Technologie (BE) and Fonds Wetenschappelijk Onderzoek. The paper does not report other conflicts of interest.

Do not read this as evidence that a sit-to-stand exoskeleton helps patients with weakness or neurologic conditions. The control was tested only in 15 non-disabled adults, and the assisted condition could not be properly evaluated because the hip motor saturated.