Biophysical Comparison between Synchronous and Asynchronous Hand Cycling

The hand cycle is a good alternative for the handrim wheelchair outdoors. the use of the hand cycle is especially an advantage in covering long distances, because it has a higher efficiency and is less straining compared to the handrim wheelchair. although hand cycling has become increasingly popular for recreational use, sports and outdoor wheeling over the last decade, today little is known about the cardiopulmonary strain in hand cycling. in general they are no differences in physiological responses between synchronous (syn) and asynchronous (asy) modes of arm crank ergometry. the purpose of this study was to determine whether gross mechanical efficiency and/or cardiopulmonary parameters are different between synchronous and asynchronous modes of hand cycling. seven untrained able-bodied male subjects performed two discontinuous submaximal incremental exercise tests on a treadmill using the hand cycle. one test was performed synchronously (cranks in parallel position and both arms moving in the same direction simultaneously) and the other one asynchronously (with the cranks in alternate position). submaximal physiological responses (i.e. oxygen uptake (vo2), ventilation (ve), heart rate (hr) and respiratory exchange ratio (rer)) were continuously measured. external power output (po in w) was calculated from the product of drag force (n) and belt velocity (v in m.s-1). energy expenditure (en) was calculated from vo2 and respiratory exchange ratio (rer: ratio between vco2 and vo2), according to (garby and astrup 1987). gross mechanical efficiency (gme) was defined as the ratio between mean power output and energy expenditure (xloo%). in the present study the differences in submaximal physiological responses and gross mechanical efficiency between syn and asy hand cycling were compared submaximally at one moderate gear and four different velocities (4, 6, 8, lokm.h-1 and 0.5d slope). over all velocities tested, anova showed a main effect of mode (p<0.05) for vo2, ve, en, hr and gme. for example for the highest velocity tested the data were (syn vs. asy, respectively): vo2 (1.04 ± 0.05 vs 1.20 ± 0.06 l.min-1), ve (28.2 ± 1.8 vs 32.3 ± 2.6 l.min-1), en (367 ± 51 vs 423 ± 62 j.s-1) and hr (117 ± 3 vs 124 ± 5 bpm). thus, synchronous hand cycling was less strenuous and more efficient than asynchronous hand cycling. the difference in efficiency might be a result of the fact that trunk muscles can help effectively in hand cycle propulsion in the syn situation. in contrast, during asy hand cycling extra muscles are activated in trunk and arms for steering and stabilisation only.