Introduction: To improve the fitness of active athletes, a training program must be properly structured, otherwise it may lead to overtraining. Monitoring heart rate variability after a submaximal graded load test could be a useful tool to determine the body's response to a training program and potential overtraining. Purpose: The aim of this thesis was to determine the relationship between heart rate variability before and after a submaximal graded load test and exercise intensity in active young long-distance runners. Methods: In this study we used a non-invasive method of heart rate measurement by electrocardiography. Seven young active runners participated in the study. Submaximal graded load test on an indoor cycle was done up to 85% of maximal heart rate and performed four times. The test consisted of 3 phases: 1) 5-min rest, 2) graded submaximal cycling, 3) passive recovery in a sitting position. We measured fSU, RMSSD, HF and LH/HF. Changes in fSU, RMSSD, HF and LH/HF during the first 3 minutes of rest and the last 3 minutes of recovery were statistically analysed and compared with exercise intensity estimated by the training stimulus method (MVD) according to the Banister model and according to the modified models considering 2-day training volume (MVD2), rest (MVDm) and subjective Borg rating of effort (LONt). The variation coefficient of the measured volumes was used to track the change in physiological response to the submaximal graded load test during the training process. Results: All measured physiological quantities varied during the training program. We found a statistically significant linear association between 䀆RMSSDpo and 䀆MVD (p = 0.047, r = -0.386), 䀆MVDm (p = 0.029, r = -0.397) and 䀆LONt (p = 0.021, r = -0.418). Discussion and Conclusion: Our results show that heart rate variability varies after submaximal graded load test and that 䀆RMSSDpo is statistically significantly associated with certain training intensity ratings. Using heart rate variability as a tool to monitor the body's response to training program and as an indicator of potential overtraining may be useful.
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