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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 HRV and BRS analyses and might provide useful markers to avoid the overtraining syndrome.