The effects of bed-rest and countermeasure exercise on the endocrine system in male adults: Evidence for immobilization-induced reduction in sex hormone-binding globulin levels

Background and aim: There is limited data on the effects of inactivity (prolonged bed-rest) on parameters of endocrine and metabolic function; we therefore aimed to examine changes in these systems during and after prolonged (56-day) bed-rest in male adults. Subjects and methods: Twenty healthy male subjects underwent 8 weeks of strict bed-rest and 12 months of follow-up as part of the Berlin Bed Rest Study. Subjects were randomized to an inactive group or a group that performed resistive vibration exercise (RVE) during bed-rest. All outcome parameters were measured before, during and after bed-rest. These included body composition (by whole body dual X-ray absorptiometry), SHBG, testosterone (T), estradiol (E-2), PRL, cortisol (C), TSH and free T-3 (FT3). Results: Serum SHBG levels decreased in inactive subjects but remained unchanged in the RVE group (p<0.001). Serum T concentrations increased during the first 3 weeks of bed-rest in both groups (p<0.0001), while E2 levels sharply rose with re-mobilization (p<0.0001). Serum PRL decreased in the control group but increased in the RVE group (p=0.021). C levels did not change over time (p >= 0.10). TSH increased whilst FT3 decreased during bed-rest (p all <= 0.0013). Conclusions: Prolonged bed-rest has significant effects on parameters of endocrine and metabolic function, some of which are related to, or counteracted by physical activity. (J. Endocrinol. Invest. 35: 54-62, 2012) (C)2012, Editrice Kurtis