title: 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.
abstract: OBJECTIVE
  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.
  
  
  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 (E2), PRL, cortisol (C), TSH and free T3 (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.
authors.affiliation: Charité University Medical School, Center for Muscle and Bone Research, Berlin, Germany. belavy@gmail.com
authors.forename: D L
authors.initials: DL
authors.lastname: Belavý
authors.forename: M J
authors.initials: MJ
authors.lastname: Seibel
authors.forename: H J
authors.initials: HJ
authors.lastname: Roth
authors.forename: G
authors.initials: G
authors.lastname: Armbrecht
authors.forename: J
authors.initials: J
authors.lastname: Rittweger
authors.forename: D
authors.initials: D
authors.lastname: Felsenberg
mesh_terms: D015502:Absorptiometry, Photon; D000222:Adaptation, Physiological; D000328:Adult; D001510:Bed Rest; D001604:Berlin; D001823:Body Composition; D004703:Endocrine System / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005081:Exercise Therapy; D005500:Follow-Up Studies; D006801:Humans; D007103:Immobilization; D008297:Male; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*
chemical_list: D012738:Sex Hormone-Binding Globulin