Bone Metabolism Is Similarly Altered Following Three Bouts Of Strenuous Exercise In Women

Military training often requires recruits to perform repeated bouts of strenuous load carriage exercise. Markers of bone metabolism are altered for several hours after strenuous exercise, but the impact of repeated bouts is less understood. PURPOSE: To characterize the effects of repeated bouts of a militarily relevant exercise on circulating bone biomarkers. METHODS: Twenty-one female participants; mean ± SD age 26.4 ± 6.7, performed three bouts of a 60 min treadmill exercise at 65% VO2peak while wearing a weight vest (30% of body weight). The three bouts (Days 1, 3, and 5) were separated by 48 h of recovery. Fasted blood samples were collected at 0530 h (AM) and the exercise (EX) commenced ~0800 h. Blood samples were collected before (PRE) and after EX at +15 min, +2 h (Day 1 only), and + 4 h. To control for circadian patterns, participants also performed a non-exercise rest week (REST) in a randomized, crossover design. Diet was controlled and replicated for each trial. Serum was assayed for osteocalcin (OCN), C-terminal propeptide of type 1 collagen (CTX), tartrate resistant acid phosphatase (TRAP5b), N-terminal propeptide of type 1 collagen (P1NP), bone alkaline phosphatase (BAP), sclerostin (SOST), Dickkopf-related protein (DKK1), fibroblast growth factor 23 (FGF23), and osteoprotegerin (OPG). EX data are expressed as % change from PRE and adjusted for changes in plasma volume from PRE. Data were analyzed using repeated measures ANOVA. RESULTS: There were no differences (p > 0.05) in AM bone turnover markers on Days 1, 3 and 5. On Day 1, post-EX increases (p < 0.05) in OCN (46.7%), SOST (40.0%), DKK1 (35.5%), FGF23 (20.3%), and OPG (29.6%) were detected as early +15 min to +2 h. The pattern of change due to EX was similar on all days with the exception of DKK1 which displayed a lower response during subsequent EX bouts. Resorption marker CTX increased after EX on Days 1 and 5 at +2 h; TRAP did not differ by trial. Formation marker P1NP only increased on Day 5 at +15 min; BAP did not differ by trial. CONCLUSIONS: Repeated bouts of EX resulted in similar post-EX changes in bone resorption and formation markers. These changes largely revert to baseline values by 4 h post-EX. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.