Relationship between shoulder pain and kinetic and temporal-spatial variability in wheelchair users

Objective To examine intra-individual variability of kinetic and temporal-spatial parameters of wheelchair propulsion as a function of shoulder pain in manual wheelchair users (MWUs). Design Cohort. Setting University research laboratory. Participants Adults with physical disabilities (N=26) who use a manual wheelchair for mobility full time (>80% ambulation). Interventions Participants propelled their own wheelchairs with force-sensing wheels at a steady-state pace on a dynamometer at 3 speeds (self-selected, 0.7m/s, 1.1m/s) for 3 minutes. Temporal-spatial and kinetic data were recorded unilaterally at the hand rim. Main Outcome Measures Shoulder pain was quantified with the Wheelchair Users Shoulder Pain Index. Intra-individual mean, SD, and coefficient of variation (CV=mean/SD) with kinetic and temporal-spatial metrics were determined at the handrim. Results There were no differences in mean kinetic and temporal-spatial metrics as a function of pain group (P values >.016). However, individuals with pain displayed less relative variability (CV) in peak resultant force and push time than pain-free individuals (P<.016). Conclusions Shoulder pain had no influence on mean kinetic and temporal-spatial propulsion variables at the handrim; however, group differences were found in relative variability. These results suggest that intra-individual variability analysis is sensitive to pain. We propose that variability analysis may offer an approach for earlier identification of MWUs at risk for developing shoulder pain.