ORIGINAL RESEARCH Heart Rate Variability, Blood Pressure Variability, and Baroreflex Sensitivity in Overtrained Athletes Mathias Baumert, PhD,*†‡ Lars Brechtel, MD,§ Ju ¨rgen Lock,¶ Mario Hermsdorf,§ Roland Wolff, MD,§ Vico Baier,* and Andreas Voss, PhD* Objective: To assess the effects of abruptly intensified physical training on cardiovascular control. Design: Retrospective longitudinal study. Setting: Research laboratory. Participants: Ten healthy athletes (5 men and 5 women) from track and field as well as triathlon. Interventions: A 2-week training camp, including daily stepwise increasing cycling tests, running of 40 minutes, and additional cycling of 60 minutes. Main Outcome Measurements: Time and frequency domain parameters of resting heart rate and blood pressure variability (HRV and BPV) and baroreflex sensitivity (BRS), before, during, and after the training camp. Results: We found significantly reduced HRV during the training camp (mean beat-to-beat interval: 1042 [937 to 1194] ms vs. 933 [832 to 1103] ms vs. 1055 [947 to 1183] ms, P , 0.01; root-mean- square of beat-to-beat interval differences: 68 [52 to 95] ms vs. 52 [38 to 71] ms vs. 61 [48 to 78] ms, P , 0.05). Further, BRS was significantly reduced: 25.2 (20.4 to 40.4) ms/mmHg vs. 17.0 (12.9 to 25.7) ms/mmHg vs. 25.7 (18.8 to 29.1) ms/mmHg, P , 0.05. These effects disappeared at a large degree after 3 to 4 days of recovery. Conclusion: Abruptly intensified physical training results in an altered autonomic cardiovascular activity towards parasympathetic inhibition and sympathetic activation that can be monitored by means of HRVand BRS analyses and might provide useful markers to avoid the overtraining syndrome. Key Words: overtraining, autonomic cardiovascular control, heart rate variability, blood pressure variability, baroreflex sensitivity (Clin J Sport Med 2006;16:412–417) INTRODUCTION Physical training has shown to influence autonomic cardiovascular control. Moderate endurance training increases parasympathetic activity and decreases sympathetic activity in the human heart at rest, which is considered a cardioprotective effect against lethal arrhythmias. 1,2 Overtraining, however, is thought to influence autonomic cardiovascular control negatively. 3,4 The overtraining syndrome or chronic fatigue, burnout, and staleness, respectively, remain a serious problem in athletes. It was estimated that 65% of national and in- ternational elite runners suffer from the overtraining syndrome at least once in their career, 5 but recreational athletes are also affected. 6,7 The overtraining syndrome is considered an imbalance between training and competition versus recovery. Budgett defined the overtraining syndrome as a condition of fatigue and underperformance, 8 often associated with frequent infections and depression that occur after hard training and competition. Overreaching, ie, short-term overtraining, re- solves within 2 weeks of adequate rest and must be dis- tinguished from long-term overtraining and can be seen as a normal part of athletic training or peaking for performance. The transition from overreaching to overtraining is blurred. 9 The overtraining syndrome has been divided into a sympathetic and a parasympathetic manifestation, and it was hypothesized that the underlying pathophysiological mechanisms include alterations of the endocrine and autonomous nervous sys- tem. 10,11 It is thought that the sympathetic form is dominant in the early stages of overtraining. In more advanced stages, the sympathetic system is inhibited, resulting in marked domi- nance of the parasympathetic system. This hypothesis is more or less based on the different patterns of observed symp- toms, 12,13 as well as on data from parameters like increased plasma catecholamine concentrations at rest, 14 an inadequate increase during exercise and decreased nocturnal catechol- amine excretions. 15 Since there is no diagnostic test available to detect overtraining, it is important to screen the athlete to exclude other causes of chronic fatigue. This study was conducted to assess the impact of increased training in the framework of a 2-week training camp on autonomic cardiovascular control in athletes. We hypoth- esized that the monitoring of heart rate and blood pressure variability (HRVand BPV) and baroreflex sensitivity (BRS) is suitable to detect autonomic changes due to abrupt increases in the training amount and might consequently be used as markers for the detection of overtraining. HRV and BPV refer to the beat-to-beat fluctuations of heart rate and blood pressure, respectively, and BRS measures Submitted for publication March 3, 2006; Accepted July 28, 2006. From the *Department of Medical Engineering, University of Applied Sciences Jena, Germany, §Institute for Sports, Humboldt University, Berlin, Germany; {real,- BERLIN-MARATHON, Berlin, Germany; †Centre for Biomedical Engineering, The University of Adelaide, Australia; and ‡School of Electrical & Electronic Engineering, The University of Adelaide, Australia. Reprints: Mathias Baumert, The University of Adelaide, School of Electri- cal & Electronic Engineering, SA 5005, Australia (email: mbaumert@ eleceng.adelaide.edu.au). Copyright Ó 2006 by Lippincott Williams & Wilkins 412 Clin J Sport Med  Volume 16, Number 5, September 2006