Optimum cycle frequencies in hand-rim wheelchair propulsion

Summary

To study the effect of different cycle frequencies on cardio-respiratory responses and propulsion technique in hand-rim wheelchair propulsion, experienced wheelchair sportsmen (WS group; n=6) and non-wheel chair users (NW group; n=6) performed wheelchair exercise tests on a motor-driven treadmill. The WS group wheeled at velocities of 0.55, 0.83, 1.11 and 1.39 m · s⁻¹ and a slope of 2°. The NW group wheeled at 0.83, 1.11 and 1.39 m · s⁻¹ and a 1° slope. In each test, a 3-min period at a freely chosen cycle frequency (FCF: 100%) was followed by four 3-min blocks of paced cycle frequencies at 60%, 80%, 120% and 140% FCF. Effects of both cycle frequency and velocity on physiological and propulsion technique parameters were studied.

Analysis of variance showed a significant effect (p<0.05) of cycle frequency on oxygen cost and gross mechanical efficiency in both the WS and NW group. This indicated the existence of an optimum cycle frequency which is close to the FCF at any given velocity. The optimum cycle frequency increased with velocity from 0.67 to 1.03 cps over the range studied (p< 0.05). Oxygen cost was ∼10% less at 100% FCF than at 60% or 140% FCF. Gross mechanical efficiency for the WS group at 100% FCF was 8.5%, 9.7%, 10.4% and 10.1%, respectively, at the four velocities. The similarity in the trend of oxygen cost and gross mechanical efficiency data in both the WS and NW groups suggests that an optimum cycle frequency is not merely a consequence of practice alone, but also reflects a physiologically determined optimum, dependent on muscle mechanics, e.g. velocity of contraction and power output of the muscles used.