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. 20 healthy male subjects underwent 8 weeks of strict bed-rest and 12 months follow-up as part of the Berlin Bed-Rest Study. Subjects were randomised 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), sex hormone-binding globulin (SHBG), testosterone (T), estradiol (E2), prolactin (PRL), cortisol (C), thyroid stimulating hormone (TSH) and free triiodothyronine (FT3).
Results. Serum SHBG levels decreased in inactive subjects but remained unchanged in the RVE group (p<.001). Serum T concentrations increased during the first 3-weeks of bed-rest in both groups (p<.0001), while E2 levels sharply rose with re-mobilisation (p<.0001). Serum PRL decreased in the CTRL group but increased in the RVE group (p=.021). C levels did not change over time (p≥.10). TSH increased whilst FT3 decreased during bed-rest (p all≤.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
