How fast is recovery of impaired glucose tolerance after 21-day bed rest (NUC study) in healthy adults?

AIM: We hypothesized that 4 days of normal daily activity after 21 days of experimental bed rest (BR) will not reverse BR induced impaired glucose tolerance. DESIGN: Glucose tolerance of seven male, healthy, untrained test subjects (age: 27.6 (3.3) years (mean (SD)); body mass: 78.6 (6.4) kg; height: 1.81 (0.04)  m; VO2 max: 39.5 (5.4) ml/kg body mass/min) was studied. They stayed twice in the metabolic ward (crossover design), 21 days in bed and 7 days before and after BR each. Oral glucose tolerance tests were applied before, on day 21 of BR, and 5 and 14 days after BR. RESULTS: On day 21 of BR, AUC(120 min) of glucose concentration was increased by 28.8 (5.2)% and AUC(120 min) of insulin by 35.9 (10.2)% (glucose: P < 0.001; insulin: P = 0.02). Fourteen days after BR, AUC(120 min) of serum insulin concentrations returned to pre-bed-rest concentrations (P = 0.352) and AUC(120 min) of glucose was still higher (P = 0.038). Insulin resistance did not change, but sensitivity index was reduced during BR (P = 0.005). CONCLUSION: Four days of light physical workload does not compensate inactivity induced impaired glucose tolerance. An individually tailored and intensified training regime is mandatory in patients being in bed rest to get back to normal glucose metabolism in a reasonable time frame.