Intense endurance training on heart rate and blood pressure variability inrunners

Physical training with incomplete recovery times can produce significant fa tigue. A study of cardiovascular responses showed that there is a sympathet ic and a parasympathetic form of fatigue. Purpose: The purpose of this expe rimentation was to measure the effects of intense endurance training on aut onomic balance through a spectral analysis study of the heart rate (HR) and systolic blood pressure (SBP). Methods: Eight elite runners were tested tw ice: after a relative rest period (RRP) of 3 wk and after an 12-wk intense training period (ITP) for endurance. At the end of each phase, the subjects were tested by means of a VO2max test and a tilt-table test. Results: The resting heart rate (HR) variability was lower (P < 0.001) in the intensive training phase. Likewise. there were differences in the low-frequency (0.04 -0.150 Hz; LF) and high-frequency (0.150-0.500 Hz; HF) components and the L F/HF ratio of the HR spectral analysis. The LF spectral power was significa ntly lower in the supine position (P < 0.05) during ITP. Upright tilting wa s accompanied by a 22.6% reduction in HF values during the rest period, whe reas in ITP the HF spectral power rose by 31.2% (P < 0.01) during tilt, cha racterizing a greater parasympathetic system control. Sympathetic control r epresented by the LF/HF ratio regressed markedly (P < 0.01) in response to the tilt test in ITP. Conclusions: The spectral analysis of SEP in the high frequencies shows that the changes in cardiac parameters are coupled with a decrease in sympathetic vasomotor control (-18%) and a reduction in diast olic pressure (-3.2%) in the response to the tilt test at the end of ITP. S pectral analysis could be a means of demonstrating impairment of autonomic balance for the purpose of detecting a state of fatigue that could result i n overtraining.