Surface strain on the dorsal metacarpus of thoroughbreds at different speeds and gaits.

Stacked rectangular rosette strain gages were used to measure surface bone strain on the dorsomedial cortex of the third metacarpal bones in 6 adult Thoroughbred horses during treadmill exercise. The peak principal compressive and tensile strains, angle of the peak strains and strain rate during loading were calculated and compared with speed and gait. At speeds from 4 to 14 m/s loading on the metacarpus resulted in compression of the dorsomedial cortex. Tension only occurred consistently in 1 forelimb of 1 horse at the walk (2 m/s). The angle of peak compression was within 10 degrees of the longitudinal axis of the bone, and the magnitude of compression was proportional to the speed of exercise. Mean maximum compressive strains in the 6 horses at 2 m/s were -668 mu strain, -1,204 mu strain at 4 m/s; -1,617 mu strain at 6 m/s; -2,127 mu strain at 8 m/s, and -2,533 mu strain at 10 m/s. Recordings from 3 horses gave a mean -3,206 mu strain at 12 m/s, and strains at 14 m/s approached -4,000 mu strain. Peak strains were similar in both forelimbs at the canter while strain rate tended to be higher in the leading forelimb.