Physiological responses to successive days of intense training in competitive swimmers

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To examine the physiological responses to successive days of intense training, 12 male collegiate swimmers doubled their training distance (4,266 ± 264 to 8,970 ± 161 m-d-1) while maintaining the intensity at (~95% VO2mak) for 10 d. Blood samples were obtained pre-exercise and immediately and 5 min after a sub-maximal (~95% VO2mak) front crawl swim (365.8 m) on days 0, 5, and 11. Swim performance was assessed from a maximal front crawl swim (365.8 m), two maximal front crawl sprints (22.9 m), and a semi-tethered swim power test. No significant changes were observed in performance. Pre-exercise serum cortisol (17.5 ± 1.5, 19.5 ± 1.6, and 20.6 ± 1.2µg- dl-1 for days 0, 5, and 11, respectively) and creatine kinase (56.2 ± 7.7, 93.1 ± 10.1, and 119.0 ± 23.1 U-l-1 for days 0, 5, and 11, respectively) values were significantly elevated (P<0.05) on days 5 and 11 compared to day 0. Resting plasma catecholamine concentrations were higher but not significantly different (P>0.05) at the end of the training period. Measurements of hemoglobin and hematocrit indicated a relative increase of 11.4 ± 2.7% (P<0.05) in estimated plasma volume during the training period. Resting blood glucose values were unaffected by the training regimen while small but significant decreases in resting blood lactate values (1.01 ± 0.06,0.85 ± 0.06, and 0.86 ± 0.06 mmol-1-1 for days 0, 5, and 11, respectively) were observed on days 5 and 11. Resting heart rate and systolic blood pressure were not affected by the increased training load. Resting diastolic blood pressure was elevated {P<0.05) on day 9 compared to day 0 (83.5 ± 1.5 vs 75.8 ± 2.2 mmHg, respectively). Serum cortisol and creatine kinase levels were elevated in all subjects even though performance was not impaired by the training protocol. Thus, the elevation of these markers appears to be a normal response to the stress of an increased training load.

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