Human sleep and adrenal individual reactions to exercise

Six fit men, aged 20, participated in the 16 day experiment. After a 5 day control period, the subjects marched on 6 consecutive days (from 09:00 h to 17:00 h) for 34 km/day at a speed of 6 km/h, with a backpack adjusted to complete a 35% of individual VO2 max energy expenditure. Control conditions were resumed for a 5 day recovery period. Sleep records were taken every night from 22:00 h to 06:00 h. Urinary 17-hydroxycorticosteroids (17-OHCS) were analysed from a 09:00 h to 17:00 h sample and from overnight urines. Two groups of subjects were defined by their responses to exercise. Four subjects exhibited an increase in stage 3 during the last third of the exercise nights (mean: 163.8 +/- 7.3% of control values) without any change in their adrenal response. Two subjects had no change or a slight decrease in stage 3 but showed increased 09:00--17:00 h 17-OHCS urine excretion (mean: 147 +/- 13% of control values). Sleep latencies were decreased in both groups. However, the 2 subjects of the second group exhibited increased restlessness as measured by the levels of wakefulness, stage 1 and EMG activity. In all subjects, paradoxical sleep was not altered, along with an unchanged all-night excretion of 17-OHCS. It is suggested that differences in adrenal responses to exercise may be responsible for differences in sleep quality. This could explain the discrepancies encountered in the literature about sleep variations after physical exercise.