Kirwan, J. P., Costill, D. L., Flynn, M. G., Mitchell, J. B., Fink, W. J., Neufer, P. D., & Houmard, J. A. (1988). Physiological response to successive days of intense training in competitive swimmers. Medicine and Science in Sports Medicine, 20, 255-259.

Highly trained swimmers (N = 12) were studied before, during, and after 10 successive days of increased training in an attempt to determine the physical effects of training overload. Training was increased from 4,266 to 8,970 m per day while intensity was maintained at 94%. Swim performance was assessed by a maximal crawlstroke swim (400 yd), two 25 yd sprints, and a semi-tethered swim power test.

No significant changes in performance were observed. Resting serum cortisol and creatine kinase were elevated after the initiation of extra training. No changes in heart rates or systolic blood pressure were observed. Hemoglobin and hematocrit were significantly decreased. Resting blood lactate was reduced to a minor but significant degree.

Implication. Hormone and metabolic indicators did not discriminate between those who could, or could not, tolerate the increased training load. Swimmers who were unable to tolerate the increased load showed depressed glycogen levels and that is offered as a better explanation for the reduced performance. Given adequate diet, well trained swimmers should be able to tolerate increases in work load for short periods of time.

Before inferring performance decrements to blood factors, the nutritional state and habits of the swimmer should first be considered.

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