The relationships between muscle weakness, wheelchair propulsion technique and upper extremity demand
There are millions of individuals throughout the world that rely on manual wheelchair propulsion as their primary method of mobility. Due to the considerable physical demand of wheelchair propulsion, these individuals are at an increased risk of developing upper extremity pain and injuries that can lead to a progressive decline in independence and quality of life. The overall goal of this research was to use a combination of experimental analyses and forward dynamics simulation techniques to gain an increased understanding of the relationships between muscle weakness, wheelchair propulsion technique and upper extremity demand. In the first study, a set of simulations was used to investigate the compensatory mechanisms that result from weakness in specific muscle groups. The simulation results suggested that the upper extremity musculature is robust to weakness in individual muscle groups as other muscles were able to compensate and restore normal propulsion mechanics. However, high stress levels and potentially harmful shifts in power generated by the rotator cuff muscles were observed. Such overuse could lead to the development of pain and injury in these muscles, suggesting that rehabilitation programs should target strengthening these muscles. In the second study, a set of objective quantitative parameters was developed to characterize kinematic hand patterns and assess the influence of propulsion speed and grade of incline on the patterns preferred by a group of 170 experienced manual wheelchair users. Increased propulsion speed resulted in a shift away from under-rim hand patterns while increased grade resulted in the hand remaining near the handrim throughout the propulsion cycle. These results identified how individuals modify their hand patterns in response to different propulsion conditions encountered in daily activities. In the third study, simulations of four commonly observed hand pattern types were generated. The simulations revealed the double loop and semi-circular patterns had the lowest overall muscle stress and total muscle power, suggesting that these hand patterns may reduce upper extremity demand. Together, the results of these studies have provided a scientific basis for designing rehabilitation and training programs aimed at reducing the prevalence of upper extremity injury and pain among individuals who use manual wheelchairs.