Altered hormonal response to short-term bicycle exercise in young men after prolonged physical strain, caloric deficit, and sleep deprivation

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Abstract
The hormonal response to a standardized bicycle exercise test was studied in 11 male cadets exposed to a course of 107 h of continuous activity with less than 2 h sleep. The subjects expended about 8,600–11,000 kcal/24 h whereas their daily food intake contained only about 1,500 kcal. The exercise test was performed once 12 days before the course (control experiment) and on day 3 and day 5 during the course, always between 0700–0900 h. A two to six fold increase was seen in the resting levels of noradrenaline, adrenaline, dopamine, and growth hormone during the course whereas a decrease was observed for thyroxine, triiodothyronine, and prolactin. Cortisol increased on day 3 and then decreased to precourse levels on day 5. The response to the exercise test during the course for all catecholamines was a further increase aboye and proportional to the raisted resting levels. Growth hormone increased by about 6–8 Μg/l both before and during the course. During the exercise test, cortisol decreased before the course whereas it increased during the course. All plasma levels of cortisol were higher on day 3 than on day 5 and in the control experiment. The post-exercise insulin increase was reduced during the course corresponding to a reduction in blood glucose levels. Prolactin decreased during and after exercise in the control experiment, whereas on day 5 the opposite response was seen. No changes in the disappearance rate of different hormones were observed during the course. The present investigation has demonstrated that prolonged strain severely affects the resting plasma levels of different hormones as well as the endocrine response to a short-term physical exercise.