Bonifazi, M., Bela, E., Lupo, C., Martelli, G., Zhu, B., & Carli, G. (1998). Influence of training on the response to exercise of adrenocorticotropin and growth hormone plasma concentrations in human swimmers. European Journal of Applied Physiology, 78(5), 394-397.

This study evaluated the response of adrenocorticotropin ([ACTH]) and growth hormone ([GH]) concentrations to a typical aerobic swimming set during a training season.

Nine top-level male endurance swimmers (age range 17-23 years) were tested during three training sessions occurring 6, 12 and 18 weeks after the beginning of the season. During each session, after a standard warm-up, the swimmers performed a training set of 15 x 200-m freestyle, with 20 s rest between repetitions, at a predetermined individual speed. Blood samples were collected before warm-up and at the end of the training set. A few days before each session, the individual swimming velocity corresponding to the 4 mmol/l blood lactate concentration was assessed as a standard of aerobic performance.

Aerobic training affected velocity levels, which were highest 18 weeks after the beginning of the season. At the same time, while [ACTH] response was attenuated, [GH] response was enhanced. These results could be considered as adaptations to the exercise intensity. These adaptations seemed to have occurred between the 12th and 18th weeks of the training season.

Implications. Swimming velocity and ACTH and growth hormone concentration changes appear to be markers of aerobic adaptation. After 12 weeks of training changes appear to be established. Thus, a coach should expect aerobic training effects to be almost fully established after three months of concerted aerobic work.

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