The purpose of the present study was to investigate the effects of increased levels of heart rate (HR) induced either by a prior strenuous exercise or heart disease on HR kinetics during the subsequent incremental exercise. Nine healthy males completed the following three sessions on different days 1 ) 10 min rest (R1) followed by a ramp work test (15 W/min) on a cycle ergometer until exhaustion (E1), 2 ) constant load exercise on a cycle ergometer at 100% of peak work rate (WR) determined in E1 until exhaustion (CL) followed by 20 min rest (R2), and 3 ) CL followed by 5 min rest and the subsequent ramp work test (E2).
　In addition, six patients with myocardial infarction were studied for the submaximal HR responses in a ramp work test (10 W/min). In all sessions, beat-to-beat R-R intervals and breath-by-breath respiratory gas exchange were monitored continuously. Resting beat-to-beat HR variability data (10 min) were analyzed by coarse-graining spectral analysis to evaluate the basal cardiac vagal tone at the beginning of the incremental exercise. The kinetics of HR during exercise were analyzed by a two-line regression method. The slopes of WR vs. HR relationships below (α-) and above (α+) ventilatory threshold were calculated.
　Although the initial HR in E2 (106.9 ± 16.3 bpm) was significantly (P< 0.05) higher than that in E1 (72.5 ± 12.7 bpm), there was no significant (P> 0.05) difference in HR as well as in WR between E1 and E2 both at ventilatory threshold and exhaustion. Consequently, α- in E2 was significantly (P< 0.05) smaller than that in E1, while α+ in E2 was not significantly (P> 0.05) different from that in E1. At R2, the cardiac vagal tone was significantly (P< 0.05) lower than those at R1. In the patients, α+ was also significantly (P< 0.05) greater thanα-. These results suggested that the increased HR or the vagal withdrawal at the beginning of the incremental exercise test modified WR vs. HR relationships only at low to moderate exercise intensity.

DESCENTE SPORTS SCIENCE Vol.16/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE