Comparison of Muscle Load, Comfort, Usability, and Time-On-Task Across 3 Wheelchair Handle Orientations and Ground Types: A Randomized Crossover Study.

BACKGROUND This study aimed to compare muscle load, comfort, usability, and time-on-task between parallel, vertical, and lateral wheelchair handle orientations on 3 ground types in 28 healthy adults pushing a 65-kg wheelchair load. The novelty of this study lies in integrating electromyographic (EMG) activity with subjective discomfort and usability measures to simultaneously evaluate physiological demand and functional performance. MATERIAL AND METHODS We used a randomized crossover design with within-participant comparisons. The study included 28 healthy adults simulating caregiving tasks. Muscle load, discomfort (Borg CR-10), usability (System Usability Scale, SUS), and time-on-task were compared among 3 handle orientations on 3 ground types while pushing a wheelchair loaded with 65 kg. Muscle load was primarily determined by the activation levels of the extensor carpi radialis (ECR), bilateral flexor carpi ulnaris (FCU), and biceps brachii (BB). RESULTS Handle orientation and ground type significantly affected EMG amplitudes in the ECR, FCU, and BB muscles (P<0.05). Parallel handles produced greater muscle activation and higher perceived discomfort than vertical and lateral handles, particularly on ramps (P<0.05). Vertical handles resulted in lower SUS scores compared to parallel and lateral handles (P<0.05). Additionally, time-on-task on the twisting cone path was longer with vertical handles than lateral handles. CONCLUSIONS In healthy wheelchair attendants, parallel handles increased upper-limb muscle load and discomfort, especially on ramps. Vertical handles reduced forearm muscle load but decreased usability, while lateral handles produced moderate activation and improved turning control, supporting ergonomic design strategies.