Kinetics and heart rate variability during aerobic exercise: influence of the intensity and the period of analyze

Abstract

The aim of this study was to describe the heart rate kinetics (FC) and how the heart rate variability (VFC) was associated with this phenomenon. Seven subjects were submitted to a cycling protocol to determine the anaerobic threshold (Lan) and the maximal aerobic power. In five subsequent tests, the subjects performed thirty minutes of a steady state exercise, corresponding to 25, 50, 75, 100 e 125% of the anaerobic threshold, respectively. The cardiac kinetic responses on and off (FC ON e FC OFF) were analyzed using exponential functions. The spectral analysis was used to describe the VFC. The parameters calculated with the exponential function were compared using an one - way repeated measures ANOVA, with pos hoc Bonferroni test. All the statistical procedures were considered significant at p < 0.05. The cardiodynamic phase was observed during the first seconds of the effort for all the subjects. The slow component was observed in the FC ON at the intensity above the Lan75. The cardiac drift was observed at an intensity of Lan75. Inversely, the FC OFF demonstrated a first exponential function, independently of the level of the effort. There was a significant difference between amplitude of the FC OFF at Lan75, Lan100 and time constants of the FC OFF at Lan100 and Lan125 when compared to the same indices at Lan25 and Lan50. The parasympathetic activity reduced in the beginning of the exercise, but increased after completion, while the sympathetic contribution did not demonstrate any association with the effort. The asymmetry between FC ON and FC OFF indicates differences between hemodynamics and neural responses associated with the cardiac control.