Abstract
Military training creates a multi-stressor environment which has been associated with risk of stress fracture. Understanding the acute bone biomarker responses to exercise can provide a model to study how various stressors or interventions affect bone and its adaptation to physical training. PURPOSE: To characterize the effects of a militarily relevant exercise on circulating bone biomarkers. METHODS: 20 Soldiers (18 male, 2 female); age 21.2±0.9 y, performed a 60 min self-paced treadmill time trial at 1% grade while wearing 30% of body weight vest (EX) and a resting control trial (CON) in a randomized, crossover design. Fasted blood samples were collected at 0630 h (AM) and EX or CON trials commenced ~0900 h. Blood samples were collected before (PRE) and after (POST) exercise, and at +1, +2, and +4 h after EX or time-matched during CON. Additionally, fasted samples were collected for the next 3 mornings at 0630 h (AM Day +1 to +3). Parathyroid hormone (PTH), ionized calcium (iCa), osteocalcin (OCN), sclerostin (SOST), C terminal propeptide of type 1 collagen (CTX), N-terminal propeptide of type 1 collagen (P1NP), bone alkaline phosphatase (BAP), and tartrate resistant acid phosphatase (TRAP5b) were assayed and all samples except AM were adjusted for changes in plasma volume from PRE. Data were analyzed using repeated measured ANOVA. Data are mean ± SE. RESULTS: Compared to PRE, PTH was significantly higher (104±32%, p<0.01) and iCa was lower (-2.5±0.8%, p<0.01) at POST during EX but not during CON. OCN was higher at +1 through +4 h than PRE by 15.9±13.0-20.5±12.0% (p<0.01) during EX but unchanged during CON. SOST was elevated by 29.1±14.2% (p<0.01) at POST vs PRE EX but later time points were not different than CON. CTX was elevated vs PRE at +1 h (43.6±22.2%, p<0.01) in EX condition only; later time points were higher (p<0.01) than PRE under both conditions. P1NP, BAP, and TRAP5b were not different from PRE during EX or CON. There were no changes in the AM Day 1-3 samples except OCN was lower than CON on Day +2 and +3. CONCLUSIONS: Consistent with prior reports, iCa decreased and PTH increased immediately post EX. Some markers of bone resorption and OCN were increased post EX. In sum, the temporal pattern of these biomarkers suggest a transient post exercise increase in resorption, but these changes disappear within 24 h after exercise.
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