Cardiorespiratory responses to cycle exercise during a low-intensity sinusoidal work rate

Purpose: Sinusoidal varying protocols have been recently re-proposed in assessing the cardiorespiratory response (CRR) to exercise to reflect the variability in long-lasting physical activities. Contrary to square-wave tests, the cyclic nature of sinusoidal work rate allows to explore the CRR kinetics several times. Previous studies used to overlap CRR of successive periods; however, so far no study assessed whether CRRs are constant along different cycles. Therefore, this study aimed at investigating the CRR during an exhausting low-intensity sinusoidal work rate. Methods: Seven subjects (age: 27 ± 7 yr, body mass: 72.5 ± 6.7 kg; stature: 1.8 ± 0.1 m) participated to the study. After determining on different days the maximum oxygen uptake (V’O2max) by ramp cycle ergometric test and critical power (CP) via different submaximal exercises, they underwent a sinusoidal work rate until exhaustion. The exercise varied according to a sinewave function with a midpoint (MP) equal to 50 W below CP (CP-50), an amplitude (A) of 50 W and a period of 4 min. Expiratory ventilation (V’E), carbon dioxide output (V’CO2), oxygen uptake (V’O2) and heart rate (HR) were obtained breath-by-breath and fitted off-line by the sinewave functions that minimized the residuals. Thereafter, A, MP and the timedelay (tD, the latency between mechanical and CRR signals) were obtained for each cycle. A one-way ANOVA for repeated measures was applied to test the effect of fatigue. Results: MP of V’E, V’O2 and HR significantly increased as well as A of V’E and V’CO2 (p\0.05 for all parameters). On the contrary, A of HR decreased during the test (p\0.05). No changes were detected on tD in all CRRs parameters. Conclusions: This study demonstrates that despite the low intensity level of the sinusoidal protocol, the dynamics of CRRs are not constant. Therefore, averaging the CRRs of different cycles might introduce a bias in the outcomes concealing a marked change in CRRs. References 1. Fukuoka Y et al. (2002) Dynamics of the heart rate response to sinusoidal work in humans: influence of physical activity and age. Clinical Science 102: 31–38 2. Miyamoto Y et al. (1983) Cardiorespiratory Dynamics during Sinusoidal and Impulse Exercise in Man. The Japanese Journal of Physiology 33: 971-986