Power output and metabolic cost of synchronous and asynchronous submaximal and peak level hand cycling on a motor driven treadmill in able-bodied male subjects

Abstract

Purpose To evaluate external power output and physiological responses of synchronous (SYNC) and asynchronous hand cycling (ASYNC) at submaximal and peak levels of exercise. Methods n = 9 able-bodied male subjects (age: 20.1 ± 2.1 years) performed two (sub)maximal continuous hand cycle exercise tests, using the SYNC and ASYNC mode in a standardized commercial add-on hand cycle unit (counter-balanced order). Treadmill speed (1.89 and 2.17 m s −1) and slope (steps of +1%) were changed in a fixed sequence of 3-min exercise steps. Gears were adjusted to 65 rpm. External power output (PO) was continuously monitored with a strain-gauge instrumented chain ring ((SRM) Schoberer Rad Messtechnik). A conventional wheelchair drag test was performed to validate mean external power for each speed-slope combination. Heart rate (HR; bpm) and oxygen uptake (VO 2; ml kg −1 min −1, SMTP) were continuously monitored. Paired T-tests and ANOVA for repeated measures evaluated effects of mode and exercise level ( p < 0.05). Results Subjects reached peak levels of performance (RER: 1.05 ± 0.07 versus 1.10 ± 0.1 for SYNC and ASYNC). Peak PO and V O 2 were significantly higher for SYNC (81.6 ± 11.8 W versus 68.5 ± 10.6 W; 26.4 ± 4.5 ml kg −1 min −1 versus 21.2 ± 3.0 ml kg −1 min −1). At submaximal exercise levels, gross mechanical efficiency (ME) was significantly higher for SYNC (12.1 ± 0.9% versus 9.7 ± 1.4% at 41 W). No significant differences were found for PO (at equal velocity and slope), as derived from the SRM (SYNC and ASYNC), and from the drag test. Discussion The absence of any differences in PO between SYNC and ASYNC, and with respect to the drag test, rules out ‘additional external work due to maintain the desired heading’ in the ASYNC as an explanation for the lower performance in this mode. Lower peak performance and ME in ASYNC may be explained by the increased stabilizing muscle effort in the upper extremities and trunk in order to combine power production with stable steering. ASYNC is less efficient compared to SYNC. Similarly, peak performance capacity was higher for SYNC. Conclusion External work does not differ between SYNC and ASYNC hand cycling. SRM readings appear valid for PO monitoring in hand cycling within the studied range of PO. SYNC is more efficient than ASYNC and leads to higher peak performance.