Effects of Endurance Training on Endocrine Response to Physical Exercise after 5 Days of Bed Rest in Healthy Male Subjects

Abstract

The study was designed to evaluate how a bout of endurance training (ET) influences the endocrine response after head-down bed rest (HDBR). Eleven healthy males completed the study, which consisted of a 6-wk ET followed by 5 days of -6 degrees head-down HDBR. Treadmill exercise at 80% of pretraining maximal aerobic capacity (VO(2max)) was performed before and after ET as well as after HDBR. ET increased VO(2max) by 13%. The response of norepinephrine was attenuated after ET and exaggerated after HDBR (P < 0.001). The differences in epinephrine responses were not statistically significant. The responses of cortisol and plasma renin activity (PRA) were unchanged after ET and were enhanced after HDBR (P < 0.001). The response of growth hormone after HDBR was reduced (P < 0.05). Only the change in cortisol response was associated with the increment of VO(2max) after ET (r = 0.68, P < 0.01). Endurance training failed to completely prevent changes in endocrine responses seen after HDBR. Improvement of physical fitness was associated with an enhancement of the cortisol response to exercise following the period of bed rest.

Influence of Exercise on the Metabolic Profile Caused by 28 days of Bed Rest with Energy Deficit and Amino Acid Supplementation in Healthy Men

“…Small increases in cortisol have been found on day 1 of BR but returned to baseline for the duration of 16 days of BR and 15 days of recovery in adults 50 . In contrast, five days of BR accompanied by an exercise intervention was associated with increased cortisol levels 51 . It is possible that the energy deficit experienced by our study participants mitigated any potential increases in cortisol with BR.…”