Response of Biochemical Markers of Bone Metabolism to Exercise Intensity in Thoroughbred Horses

We studied the response of biochemical markers of bone metabolism to exercise intensityin horses. Four horses were walked on a mechanical walker for one week (pre-exercise).Then they performed low-speed exercise on a high-speed treadmill in the first week andmedium-speed exercise in the second week and high-speed exercise in the third week oftraining. We measured two indices of bone resorption, serum hydroxyproline concentrationand the urinary deoxypyridinoline/creatinine ratio, and serum osteocalcin (OC)concentration as an index of bone formation. Both indices of bone resorption graduallydecreased during the experiment. Serum OC concentration did not change in the first weekbut was significantly lower in the second and the third weeks compared to in thepre-exercise period and in the first week. These results suggest that the low-speedexercise decreased bone resorption but did not affect bone formation, which possiblyresults in increasing bone mineral content and strengthening of bones. The high-speedexercise decreased bone formation and bone resorption, i.e., bone turnover was suppressed.The low-speed exercise may be preferable for increasing bone mineral content.