Reasons for performing study: It is considered that specific exercises to strengthen limb musculature would be helpful.
Objective: To describe swing phase kinematic and kinetic changes in the hindlimbs of trotting horses in response to the addition of leg weights to the hind pasterns.
Methods: Six horses were prepared by placing reflective skin markers on the hindlimbs, the withers and fore hooves. Horses were evaluated at trot for 6 trials with and without leg weights (700 g) attached around the pasterns, with the 2 conditions applied in random order. The markers were tracked to determine peak heights of the flight arc of the hind hooves and swing phase joint angulations. Inverse dynamic analysis was used to calculate positive and negative work done across each joint in the first and second halves of the swing phase. Comparisons between conditions were made using paired t tests (normally distributed data) or the Wilcoxon rank-sum test (non-normally distributed data).
Results: Peak height of the flight arc of the hind hooves was significantly higher with leg weights as a result of increased flexions of the stifle, tarsal and metatarsophalangeal joints. Increased positive (concentric) work was performed by the hip and tarsal musculature to protract and raise the limb in early swing, then to retract and lower the limb in late swing. Increased negative (eccentric) work was performed across the stifle and metatarsophalangeal joints to control their movements in response to increases in inertia and momentum due to the weights.
Conclusions: The addition of weight to the hind pasterns stimulates increased muscular activity across all the hindlimb joints from the hip to the metatarsophalangeal joint.
Clinical significance: The addition of weight to the hind pasterns may have therapeutic applications in activating and strengthening the hindlimb musculature. This is particularly relevant in the hip region, which appears more sensitive and responsive to the effect of weights than to tactile stimulation alone.