The role of exercise intensity in the bone metabolic response to an acute bout of weight-bearing exercise

Abstract

We compared the effects of exercise intensity (EI) on bone metabolism during and for 4 days after acute, weight-bearing endurance exercise. Ten males [mean ± SD maximum oxygen uptake (V̇o2max): 56.2 ± 8.1 ml·min−1·kg−1] completed three counterbalanced 8-day trials. Following three control days, on day 4, subjects completed 60 min of running at 55%, 65%, and 75% V̇o2max. Markers of bone resorption [COOH-terminal telopeptide region of collagen type 1 (β-CTX)] and formation [NH2-terminal propeptides of procollagen type 1 (P1NP), osteocalcin (OC), bone-alkaline phosphatase (ALP)], osteoprotegerin (OPG), parathyroid hormone (PTH), albumin-adjusted calcium (ACa), phosphate (PO4), and cortisol were measured during and for 3 h after exercise and on four follow-up days (FU1–FU4). At 75% V̇o2max, β-CTX was not significantly increased from baseline by exercise but was higher compared with 55% (17–19%, P < 0.01) and 65% (11–13%, P < 0.05) V̇o2maxin the first hour postexercise. Concentrations were decreased from baseline in all three groups by 39–42% ( P < 0.001) at 3 h postexercise but not thereafter. P1NP increased ( P < 0.001) during exercise only, while bone-ALP was increased ( P < 0.01) at FU3 and FU4, but neither were affected by EI. PTH and cortisol increased ( P < 0.001) with exercise at 75% V̇o2maxonly and were higher ( P < 0.05) than at 55% and 65% V̇o2maxduring and immediately after exercise. The increases ( P < 0.001) in OPG, ACa, and PO4with exercise were not affected by EI. Increasing EI from 55% to 75% V̇o2maxduring 60 min of running resulted in higher β-CTX concentrations in the first hour postexercise but had no effect on bone formation markers. Increased bone-ALP concentrations at 3 and 4 days postexercise suggest a beneficial effect of this type of exercise on bone mineralization. The increase in OPG was not influenced by exercise intensity, whereas PTH was increased at 75% V̇o2maxonly, which cannot be fully explained by changes in serum calcium or PO4concentrations.