The Effect of Training Status on the Metabolic Response of Bone to an Acute Bout of Exhaustive Treadmill Running

Context: Strenuous exercise increases bone resorption but not formation. The effect of improved training status is unknown. Objective: Our objective was to examine the metabolic response of bone to strenuous running in recreationally active (RA) and endurance-trained (ET) men. Design: Eleven RA, 10 ET, and 10 control (CON) subjects completed one 8-d trial. On d 4, RA and ET completed an exhaustive treadmill run. Blood was obtained at baseline (BASE), during exercise, during 2 h of recovery, and on four follow-up (FU) days (FU1-FU4). CON rested throughout, providing blood samples at BASE and on FU1-FU4. Markers of bone resorption [C-terminal telopeptide region of collagen type 1 (beta-CTX)] and bone formation [N-terminal propeptides of procollagen type 1 (P1NP) and bone alkaline phosphatase (ALP)], osteoprotegerin (OPG), PTH, albumin-adjusted calcium (ACa), and phosphate (PO4) were measured. Results: There were no significant differences between ET and RA and no changes in CON for any variable. Exercise increased beta-CTX at FU1-FU4 (P < 0.001) but had no effect on P1NP or bone ALP. OPG was increased after 20 min of exercise (P < 0.001) and remained elevated at FU1 (P < 0.001). PTH, ACa, and PO4 were increased throughout exercise (P < 0.01). ACa and PO4 remained elevated in the 2 h after exercise (P < 0.001), where as PTH was lower than BASE from 1-2 h after exercise (P < 0.001). Conclusion: After acute, exhaustive running, bone resorption but not formation was increased for 4 d in RA and ET men. The increased bone resorption might be related to the increase in PTH, whereas increased OPG might be a compensatory response to increased bone resorption. Training status did not significantly affect the metabolic response of bone to exhaustive running. (J Clin Endocrinol Metab 95: 3918-3925, 2010)