THE EFFECTS OF INCREASED TRAINING VOLUME ON HEART RATE VARIABILITY AMONG YOUNG ENDURANCE ATHLETES

Abstract

Heart rate variability (HRV) has been used as an indicator of autonomic nervous system activity. These HRV measurements have also provided a promising research tool for studying the overtraining syndrome. PURPOSE: To examine the influence of increased volume of aerobic training on HRV, self reported feelings of exertion, and recovery among young endurance athletes. METHODS: Seventeen trained endurance athletes (aged 18–20) participated in this study. During a 5-day training camp, the total time used for aerobic training was gradually increased from 1–1 hours to 2–3 hours per day. In the first and last morning of the training camp the athletes performed two active orthostatic tests (AOT) from either supine or sitting position to standing position. RR-data were recorded with Polar VNV heart rate monitors (Polar Electro, Kempele, Finland) and analyzed with Polar Precision Performance 2.1 Software. Every morning the athletes filled in a questionnaire on the feelings of exertion and recovery during the previous 24 hours. In the first and last evening a 5km running test at set submaximal heart rate was performed. RESULTS: The changes in HRV in AOT during the training camp were greater in sit-stand test than in sup-stand test. Significant decrease in sitting and standing heart rate and increase in sitting and standing high frequency power (HFP) from the first to the last morning were found. The results showed also a significant increase in the feelings of physical exertion and decrease in the feelings of recovery. Average time in the running test was shorter, and the rated physical exertion (RPE) after the running test was higher in the last as compared to the first evening. CONCLUSION: These results suggest higher parasympathetic tone at the end of the training camp. Average speed in the running test (5km) at set submaximal heart rate increased, suggesting short-term training effect in five days. In contrast to the HRV changes, increased RPE during the running test, increased physical exertion and compromised recovery feelings suggested overreaching. AOT from sitting to standing position seems to be more sensitive to indicate changes in HRV than the traditional AOT from supine to standing position.