The overall aim of the work behind this thesis was to describe the immune, endocrine and metabolic changes occurring in elite athletes during an exhaustive endurance race, during periods with different training and competition load, and during repeated bouts of exercise intercepted by different recovery regimes.

Study I

In study I we examined the magnitude of change in immune, hormonal, substrate and metabolic variables during a long distance ski race among 10 male and 6 female international cross-country skiers. From before to immediately after the race, we found increases in the concentrations of granulocytes, natural killer (NK) cells, epinephrine (EPI), norepinephrine (NE), growth hormone (GH), cortisol, glucose, free fatty acid, creatine kinase, uric acid, inorganic phosphate, and a decrease in insulin concentration. Several of the changes in indices of immune, endocrine and metabolic functions were extensive and generally larger than what has been observed after marathon running, but did not reach levels considered to increase the health risk of the athlete.

Study II

In study II we studied the impact of variations in seasonal training and competition load (TC-score) on the acute response to exhaustive exercise in 10 male, international cross-country skiers. We tested the hypothesis that increased training and competition load would result in more pronounced stress responses in connection with an exhaustive exercise test. We found the TC-score to be twice as high during the in-season compared with the off-season period. However, during and after a standardized exercise test, there was no difference in the magnitude of change in concentrations of neutrophils, lymphocytes, EPI, ACTH, or cortisol, between the in-season HI and off-season LO tests, and only minor differences between norepinephrine and the IL-6 concentrations. Thus, alterations in chronic physical and mental stress do not seam to affect the physiological stress response to a single exhaustive exercise session.

Study III

Study III examined the impact of a previous bout of strenuous endurance exercise on the responses to a subsequent exercise bout the same day, and tested the hypothesis that immune, endocrine, and metabolic responses would be more pronounced during and after a second bout compared with a single bout of exercise. Compared with the single bout of exercise, the second bout resulted in higher plasma concentrations in EPI, NE, ACTH, cortisol, and GH; similar concentrations in insulin, FSH, LH, TSH, F-T4, IGF-1, and glucose; higher concentrations of total leukocytes, neutrophils, lymphocytes, CD4+, CD8+, and CD56+ cells; reduced NK-cell activation, higher levels of plasma IL-6 and IL-1ra; higher mean O₂ uptake, heart rate (HR), rectal temperature (T_R), excess post-exercise oxygen consumption (EPOC) and lower respiratory exchange ratio (RER). Thus, for the most part, our results confirmed the hypothesis.

Study IV

Study IV examined the impact of different recovery periods between two daily exercise sessions on the responses to a second bout of exercise, and tested the hypothesis that changes in neuroendocrine, immune, and metabolic variables elicited by the second bout of exercise would be more pronounced when preceded by a short compared with a long rest. Compared with the long rest between the exercise bouts, the short rest resulted in higher plasma concentrations EPI, NE, ACTH, cortisol and insulin; similar concentrations in GH, FSH, LH, TSH, F-T4, IGF-1, and glucose; higher concentrations of neutrophils; similar concentrations of CD4, CD8, CD56 cells, IL-6, and IL-1ra; similar lymphocyte activation; lower post-exercise lymphocyte concentrations; higher O₂ uptake, HR, T_R, and lower RER. For the most part, our results confirmed the hypothesis.

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