Immobilization by 21 days of bed rest results in type II collagen degradation in healthy individuals

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To investigate the effects of 21 days of bed rest immobilization (with and without exercise and nutrition interventions) on type II collagen biomarker concentrations in healthy individuals. Twelve healthy male participants (age 34.2±8.3years; body mass index 22.4±1.7kg/m²) were exposed to 6days ambulatory baseline data collection (BDC), 21days head-down-tilt bed rest (HDT, CON)+interventions (HDT+resistive vibration exercise (2 times/week, 25minutes): RVE; HDT+RVE+whey protein (0.6g/kg body weight/day) and bicarbonate supplementation (90mmol KHCO3/day: NeX), and 6days of re-ambulation (R) in a cross-over designed study. The starting HDT condition was randomized (CON-RVE-NEX, RVE-NEX-CON, NEX-CON-RVE). Blood and urine samples were collected before, during, and after HDT. Serum concentrations (s) of CPII, C2C, C1,2C, and urinary concentrations (u) of CTX-II and Coll2-1NO2 were measured. Twenty-one days of HDT resulted in increased sCPII (p < 0.001), sC2C (p < 0.001), and sC1,2C (p=0.001) (highest increases: sCPII (+24.2% - HDT5), sC2C (+24.4% - HDT7), sC1,2C (+13.5% - HDT2). sC2C remained elevated at R+1 (p=0.002) and R+6 (p < 0.001) compared to baseline. NeX led to lower sCPII (p < 0.001) and sC1,2C (p = 0.003) compared to CON. uCTX-II (second void and 24-hour urine) increased during HDT (p < 0.001, highest increase on HDT21: second void +82.8% (p < 0.001); 24-hour urine+77.8% (p < 0.001). NeX resulted in lower uCTX-II concentrations in 24-hour urine (p = 0.012) compared to CON. Twenty-one days of bed rest immobilization results in type II collagen degradation that does not recover within 6days of resuming ambulation. The combination of resistive vibration exercise and protein/bicarbonate supplementation minimally counteracted this effect.