Fast "ON" and "OFF" heart rate transients at different bicycle exercise levels.

Rapid heart rate (HR) changes take place at the onset and at the end of exercise. The aim of this study was to analyze these changes at different exercise levels. A total of 17 healthy men (23 +/- 4 yrs), who without being told the aim of the study pedaled an electrically braked bicycle at 60 rpm "ON" transients, were studied during changes in work rates from 0 to 1, from 1 to 2, and from 2 to 4 W.kg-1. "OFF" transients were measured from 4 and from maximal work rate to 0 W.kg-1. The ECG was recorded starting from 5 s before until 15 s after each work rate change. The mean HR was calculated at 2.5 s intervals as delta % HR - the heart rate change as percent of the final pretransition value. Linear regressions between delta % HR and time were obtained for each transient and their angular coefficients compared. Of the ON transients only the 2nd and 3rd suggested differences, while the OFF transients did not differ significantly. All of the transients were reproducible for a given subject (P greater than 0.05). The parasympathetic blockade performed in two subjects produced slower transients (except for the 1st ON). VO2max was determined at the end of a continuous progressive test, performed after the 1st OFF. No correlation was found between the transients and VO2max (P greater than 0.05). In conclusion, within 15 s, the ON and OFF transients showed changes of 10% and 5%, respectively, in HR. They were primarily mediated by the vagus.(ABSTRACT TRUNCATED AT 250 WORDS)