A New Method to Quantify Demand on the Upper Extremity During Manual Wheelchair Propulsion

Objective To use an ergonomics-based rating that characterizes both demand on, and capacity of, upper-extremity muscle groups during wheelchair propulsion to help identify the muscle groups most at risk for pain or overuse injury in a relatively demanding wheelchair propulsion task. Design Case series. Setting Biomechanics research laboratory. Participants Sixteen manual wheelchair users with complete (American Spinal Injury Association grade A) T6-L2 paraplegia. Interventions Not applicable. Main outcome measures Internal peak joint moments required by each of the major upper-extremity muscle groups for propelling a wheelchair up a ramp; isometric strength of each of the muscle groups in positions simulating wheelchair propulsion; and wheelchair propulsion strength rating (WPSR) for each muscle group, calculated by normalizing the joint demands to their capacity. Results The largest joint moment was for shoulder flexion, at 39.7±13.9Nm. Shoulder flexion also accounted for the peak WPSR value of 66.5%±20.3%. Supination and pronation movements had low peak moment requirements (3.4Nm, 5.0Nm, respectively) but high WPSR values (41%, 53%, respectively). Conclusions Even a relatively benign ramp (2.9°) places a large demand on the musculature of the upper extremity, as assessed by using the WPSR to indicate muscular demand

The Effect of Seat Position on Wheelchair Propulsion Biomechanics

This study examined the effect of seat position on handrim biomechanics. Thirteen experienced users propelled a wheelchair over a smooth level floor at a self-selected speed. Kinetic and temporal-distance data were collected with the use of an instrumented rim and a motion analysis system. A custom-designed axle was used to change the seat position. We used repeated measures analysis of variance to evaluate if differences existed in the temporal-distance and kinetic data with change in seat position. Results showed that a shorter distance between the axle and shoulder (low seat height) improved the push time and push angle temporal variables (p \u3c 0.0001). Tangential force output did not change with seat position. Axial and radial forces were highest in the lowest seat position (p \u3c 0.001). Propulsion efficiency as measured by the fraction of effective force did not significantly change with seat position