RELATIONSHIP BETWEEN TRAINING RESPONSE AND HEART RATE VARIABILITY IN ENDURANCE ATHLETES

Abstract

The effects of long-term training period on cardiac autonomic function in athletes is not well known. PURPOSE This study was designed to assess the relationship between training response and cardiac autonomic function in endurance athletes over 5 months. METHODS Fifteen national level cross-country skiers (8 male 21±4 years; 7 female 17±1 years) and 7 sedentary control subjects were studied during the training season (Sep 2001) and during the competition season (Jan 2002). An incremental treadmill test was performed until exhaustion and the time to exhaustion used as maximal performance index. The R-R intervals were recorded at rest, during 80° passive head-up tilt test (5-min) and during each 3-min load of treadmill test. The vagally mediated beat-to-beat R-R interval fluctuation (SD1) was analyzed by two-dimensional vector analysis method from Poincaré plot at rest, during tilt test and during exercise. The relationship between individual changes in time to exhaustion and heart rate behaviour was analyzed. RESULTS The change in exhaustion time (+2.0±8.0 %, range from +14 to −13 %) correlated with the change in heart rate (r = 0.62, p = 0.012) and with the change in beat-to-beat heart rate variability (r = 0.60, p = 0.018) measured during passive head-up tilt test. The change in exhaustion time correlated strongly also with the change in heart rate and with the change in beat-to-beat heart rate variability measured during exercise, e.g. at the level of 55±9% of VO2max correlations were r = −0.68 (p = 0.005) and r = 0.81 (p = 0.001) respectively. The changes in heart rate behaviour at rest were not associated with changes in maximal performance. Changes in control group were not observed. CONCLUSION Increased vagal modulation of HR during passive head-up tilt test and during submaximal exercise is associated with improved performance after long-term training period in endurance athletes.