Upper-Limb Joint Power and Its Distribution in Spinal Cord Injured Wheelchair Users: Steady-State Self-Selected Speed Versus Maximal Acceleration Trials

Price R, Ashwell ZR, Chang MW, Boninger ML, Koontz AM, Sisto SA. Upper-limb joint power and its distribution in spinal cord injured wheelchair users: steady-state self-selected speed versus maximal acceleration trials. Objective: To compare upper-limb joint power magnitude and distribution between the shoulder, elbow, and wrist during maximal acceleration (MAC) versus steady-state, self-selected speed (SSS) manual wheelchair propulsion. Design: Cross-sectional biomechanic study. Setting: Research university and teaching hospital. Participants: Volunteer sample of 13 manual wheelchair users with spinal cord injury below T1. Interventions: Not applicable. Main Outcome Measures: Propulsive joint power magnitude and fractional distribution among upper-limb joints. Results: Wilcoxon signed-rank testing revealed shoulder power was larger for MAC versus SSS (median peak, 101.5W; interquartile range [IQR], 74.6; median peak, 37.7W; IQR, 22.9; respectively) (P<.01). Elbow and wrist power were unchanged. Peak shoulder power fraction was larger for MAC versus SSS (median peak, 1.055; IQR, .110 vs peak, .870; IQR, .252) (P<.01). Peak elbow power fraction was smaller for MAC versus SSS (median peak, -.012; IQR, .144 vs peak, .146; IQR, .206) (P<.05). Peak wrist power fraction was smaller for MAC versus SSS (median peak, -.058; IQR, .057 vs peak, -.010; IQR, .150) (P<.05). Conclusions: Power at the shoulder was larger than at other joints. Peak shoulder joint power and power fraction was larger during MAC versus SSS propulsion. Elbow and wrist power fractions were smaller for MAC versus SSS propulsion. Higher joint power, present under MAC, may predispose manual wheelchair users to injury, particularly at the shoulder.