Changes in thyroid hormones and lipids in endurance trained volunteers during acute and rigorous bed rest conditions

The aim of this study was to evaluate the effect of an acute rigorous bed rest (ABR) (abrupt confinement to a rigorous bed rest regimen) and a rigorous bed rest (RBR) regimen on serum concentrations of thyroid hormones and lipids. The studies were done during seven days of a pre bed rest period and during seven days of an ABR and RBR period. Thirty endurance trained male volunteers aged 22 to 26 years with a peak oxygen uptake of 66.0 mL.min-1.kg-1 and running an average of 14.0 km.day-1 were chosen as subjects. They were divided equally into three groups: (one) ten athletes placed under ambulatory conditions served as ambulatory control subjects (ACS), (two) ten athletes subjected to an acute rigorous bed rest regimen served as acute bed rested subjects (ABRS) and (three) ten athletes submitted to a rigorous bed rest regimen served as rigorous bed rested subjects (RBRS). For the simulation of the effect of ABR the ABRS group was submitted abruptly to a rigorous bed rest regimen. They did not have any prior knowledge of the exact date and time when they would be asked to submit to the RBR. For the simulation of the effect of RBR the RBRS group was subjected to a rigorous bed rest regimen on a predetermined date and time known to them right from the start of the study. During the pre bed rest period and during the ABR and RBR periods serum concentrations of thyroxine (T3), triiodothyronine (T4), thyroid-stimulating hormone (TSH), cholesterol, triglycerides, total protein and albumin were measured. In the ABRS and RBRS groups serum concentrations of T3, T4, TSH, cholesterol, triglycerides, total protein and albumin increased significantly when compared with the ACS group. Serum concentrations of thyroid hormones and lipids in the ABRS group increased much faster and were more pronounced than in the RBRS group. It is concluded that exposure to RBR and, especially, to ABR conditions induces significant increases in serum concentrations of thyroid hormones and lipids. These changes occurred much earlier and were much greater in the ABRS group than in the RBRS group.