Effect of velocity on shoulder muscle recruitment patterns during wheelchair propulsion in nondisabled individuals:...

This study investigated how the recruitment patterns of shoulder muscles were influenced by wheelchair propulsion speed. Electromyography (EMG) activity of seven muscles was recorded with surface electrodes on 15 nondisabled subjects during wheelchair propulsion on a stationary ergometer. Kinetic data were measured by a SmartWheel. EMG total intensities were calculated to describe the muscle activation level, while the angles formed by first principal component and second principal component loading scores were calculated to describe the spectral content of EMG signals. Significant differences were observed in kinetic variables between the two testing speeds (p < 0.05). The EMG intensity of the tested muscles increased significantly with increased speed (p < 0.05). The push muscles showed a longer EMG duration, whereas the recovery muscles exhibited significantly earlier EMG onset and peak activities at the fast speed. The smaller angle values in the fast propulsion speed indicated that faster motor units were recruited to match the mechanical requirement for the faster motion. Pushing a manual wheelchair at a faster speed not only requires a higher level of propulsive muscle activity but also a higher level of recovery muscle activation.