Monitoring the effects of treadmill exercise on bone by non-invasive means during a progressive fitness programme.

Six Standardbred horses underwent a 14-week training programme on a treadmill. The training schedule consisted of five weeks of slow work of six to 12 km/day at 5 m/sec. This was followed by a nine week interval programme increasing in its intensity so that for the last three weeks the horses did three to four intervals/day from 600 to 1000 m at or above maximum heart rate. Ultrasound velocity through the third metacarpus showed a significant increase as a result of training. There was also a significant increase in modulus of elasticity, but no change in bone mineral content, bone mineral density or compact bone density. A decrease in ultrasound velocity was noted immediately after a session of trotting on the treadmill for 6 km. These changes reflected the potential to alter the viscoelastic properties of cortical bone through treadmill exercise, but did not explain the mechanism involved.