The effects of backrest thickness on the shoulder muscle load during wheelchair propulsion.

[Purpose] This study investigated the optimal thickness of the wheelchair backrest for lumbar load and increased comfort. [Subjects] Fifteen healthy people participated. [Methods] The study examined three randomized backrest conditions: no pad; a 3-cm-thick lumbar pad; and a 6-cm-thick lumbar pad. The location of the lumbar pad was standardized at the mid-lumbar level (L3). Participants were instructed to propel the wheelchair using only the handrims. [Results] Activation of the anterior deltoid, upper trapezius, and biceps brachii muscles was significantly reduced when the participants used the 3-cm pad compared to no pad, while it was significantly increased in the anterior deltoid, upper trapezius, posterior deltoid, and biceps brachii when the participants used the 6-cm pad compared to the 3-cm pad. Muscle activation did not differ significantly between the no pad and the 6-cm lumbar pad conditions. [Conclusion] A lumbar pad decreased the activation of the upper extremity muscles. We believe that padding of the appropriate thickness will lead to effective muscle activation while propelling a wheelchair and decrease the risk of musculoskeletal disease.