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

doi:10.1196/annals.1296.070

^aInstitute of Experimental Endocrinology Slovak Academy of Sciences, Bratislava, Slovakia
^bFaculty of Physical Education and Sports, Comenius University, Bratislava, Slovakia
^cHospital of the Ministry of Defense, Bratislava, Slovakia

Address for correspondence: Juraj Ko $s$ ka, MD, National Institute of Diabetes & Digestive & Kidney Diseases, NIH, 4212 N. 16th St., Rm. 5-33, Phoenix, AZ 85016, USA. Voice: 602-200-5328; fax: 602-200-5335. e-mail:jkoska{at}mail.nih.gov
Ann. N.Y. Acad. Sci. 1018: 569-575 (2004).

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 consistedof a 6-wk ET followed by 5 days of –6° head-down HDBR.Treadmill exercise at 80% of pretraining maximal aerobic capacity(VO_2max) was performed before and after ET as well as afterHDBR. ET increased VO_2max by 13%. The response of norepinephrinewas attenuated after ET and exaggerated after HDBR (P < 0.001).The differences in epinephrine responses were not statisticallysignificant. 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 associatedwith the increment of VO_2max after ET (r = 0.68, P < 0.01).Endurance training failed to completely prevent changes in endocrineresponses seen after HDBR. Improvement of physical fitness wasassociated with an enhancement of the cortisol response to exercisefollowing the period of bed rest.