The effect of training status on the metabolic response of bone to an acute bout of exhaustive treadmill running.

Abstract

Strenuous exercise increases bone resorption but not formation. The effect of improved training status is unknown. Our objective was to examine the metabolic response of bone to strenuous running in recreationally active (RA) and endurance-trained (ET) men. 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. 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), whereas PTH was lower than BASE from 1-2 h after exercise (P<0.001). 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.