Abstract
OBJECTIVE: To investigate the effects of 21 days bed rest immobilization (with and without exercise and nutrition intervention) on serum concentrations of cartilage homeostasis biomarkers in healthy individuals. DESIGN: Twelve male volunteers (age 34.2 ± 8.3 years; BMI 22.4 ± 1.7 kg/m(2)) participated in 6 days of baseline data collection (BDC), 21 days of 6° head-down-tilt (HDT) bed rest (CON) + interventions HDT + resistive vibration exercise (RVE; 2 times/week; 25 min) and HDT + RVE + nutrition (NeX; 0.6 g/kg body weight/day whey protein and 90 mmol KHCO(3)/day bicarbonate supplementation), and 6 days of recovery (R) in a cross-over designed study. The starting HDT condition was randomized (CON-RVE-NeX, RVE-NeX-CON, NeX-CON-RVE). Blood samples were collected before, during and after HDT. Serum concentrations of COMP, MMP-3, MMP-9, YKL-40 and resistin were analyzed. RESULTS: The main effect of time was significant for all biomarkers tested (p < 0.001). While COMP (-36 % at HDT5, p < 0.001) and MMP-3 (-36 % at HDT21, p < 0.001) decreased during HDT bed rest, MMP-9 (+18 % at HDT5, p < 0.001) and resistin (+13 % at HDT21, p < 0.001) increased during HDT bed rest. Interestingly, during recovery, YKL-40 levels increased (+13 % at R1, p = 0.022), while MMP-9 levels decreased (-19 % at R6, p = 0.035). We identified correlations between COMP and MMP-3 (r(rm) = 0.58, p < 0.001) as well as between MMP-9 and resistin (r(rm) = 0.58, p < 0.001). CONCLUSIONS: Immobilization affects serum concentrations of cartilage homeostasis biomarkers suggesting changes in cartilage metabolism that do not completely recover during re-ambulation. Both interventions had only minimal effects.