SHOULDER JOINT KINETICS DURING THE PUSH PHASE OF WHEELCHAIR PROPULSION

The purpose of this investigation was to quantify the forces and momen ts at the shoulder joint during free, level wheelchair propulsion and to document changes imposed by increased speed, inclined terrain, and 15 minutes of continuous propulsion, Data were collected using a six-c amera VICON motion analysis system, a strain gauge instrumented wheel, and a wheelchair ergometer, Seventeen men with low level paraplegia p articipated in this study, Shoulder joint forces and moments were calc ulated using a three-dimensional model applying the inverse dynamics a pproach. During free propulsion, peak shoulder joint forces were in th e posterior (46 N) and superior directions (14 N), producing a peak re sultant force of 51 N at an angle of 185 degrees (180 degrees = poster ior), Peak shoulder joint moments were greatest in extension (14 Newto n-meters [Nm]), followed by abduction (10 Nm), and internal rotation ( 6 Nm). With fast and inclined propulsion, peak vertical force increase d by greater than 360 %, and the increase in posterior force and shoul der moments ranged from 107% to 167%, At the end of 15 minutes of cont inuous free propulsion, there were no significant changes compared wit h short duration free propulsion. The increased joint loads documented during fast and inclined propulsion could lead to compression of suba cromial structures against the overlying acromion.