Hormonal changes in serum in young men during prolonged physical strain

Summary The endocrine response to severe physical strain including lack of sleep has been investigated in army personnel during a combat course of 5 days' duration. The thyroxine (T₄) concentration in serum increased during the first 24 h, and then declined at a rate corresponding to a halflife of 7.6 days and on day 6 reached the lowest level, 55 ng/ml. Triiodothyronine (T₃) displayed a similar pattern, although an increase during the first 24 h could not be demonstrated. Within 48 h after the course T₄ had returned to normal, whereas the serum level of T₃ was significantly below the level before the course (p<0.05). The serum level of TSH was suppressed during the course.The serum level of prolactin was significantly suppressed and growth hormone was markedly elevated during the course with a significant negative correlation (r=–0.6) between the two. In agreement with a previous report, there was a rapid and sustained suppression of the serum level of testosterone to a mean level of 1.1 ng/ml on day 5.Short periods of sleep (3–6 h) were shown to be effective in reversing the changes described in this paper, especially for growth hormone, prolactin, and testosterone.This study represents a part of a research programme by the Stress Research Group of the Norwegian Joint Medical Services