1268 - Physiological Response to Increasing Manual Wheelchair Propulsion Workload

Objectives: Assess the physiological response to increasing workload when individuals can adjust their preferred propulsion speed.

Design: N=11 (male=7, female=4) non-disabled adults (mean (SD)); age 24 years (2), BMI 23.8 kg/m2(4.3) completed N=16 one minute manual wheelchair propulsion trials on a computer-controlled wheelchair ergometer at a self-preferred propulsion speed. Trials represented each 5% increment in estimated maximal workload from 25% to 100% (25%, 30%, 35%, etc.). Preferred speed (m/s), rolling resistance (N), and average oxygen consumption (ml/kg/min) from the last 20 seconds of each trial were extracted from a force and moment sensing wheelchair wheel fixed to the right side of the wheelchair and indirect calorimetry.

Results: Oxygen consumption was weakly related to workload (0.28 repeated measures correlation coefficient (rmcorr), p< 0.01), and was on average 26% (standard deviation (SD=34%) greater at 100% workload vs. 25% workload (7.6 ml/kg/min (SD=1.8) vs. 6.4 ml/kg/min (SD=2.0)). Preferred speed and rolling resistance were strongly related to workload (-0.85, -0.91 rmcorr respectively, both p< 0.01). Speed on average was 39% (SD=14%) lower at 100% workload vs. 25% workload (0.52 m/s (SD=0.11) vs. 0.87 m/s (SD=0.20)). Rolling resistance was on average 342% (SD=265%) greater at 100% vs 25% workload (53 N (SD=17) vs. 14 N (SD=5)).

Conclusions: When external workload increases, individuals appear to limit oxygen consumption by decreasing preferred propulsion speed. In community settings, enabling greater propulsion speed may require increasing the exercise capacity of wheelchair users and/or decreasing the rolling resistance of their wheelchair.