INTERRELATIONSHIPS BETWEEN MOISTURE-CONTENT OF THE TRACK, DYNAMIC PROPERTIES OF THE TRACK AND THE LOCOMOTOR FORCES EXERTED BY GALLOPING HORSES

Three methods were used to examine the relationships between the dynam ic properties of a track and the locomotor forces exerted by galloping horses. The impact resistance and the percentage of energy returned b y the track were determined using a trailer mounted track testing devi ce, Vertical forces were measured from instrumented horseshoes nailed to all four hooves and the velocities of each of the six horses gallop ing in a track straight-away were determined from slow-motion films. T he moisture content of the track was altered by the addition of water. These data were analyzed to determine the relationships between chang es in moisture content on the energy returned by the track, impact res istance of the track and locomotor forces exerted by the horses, There was a strong linear relationship between impact resistance and the pe rcentage of energy returned by the track, Changes in moisture content of the track cushion resulted in similar changes in both the percentag e of energy returned and the impact resistance of the track. Energy re turn and impact resistance decreased at 8% moisture and progressively increased from 8.5 to 14% moisture.The horses were divided into two gr oups based upon their speed during each trial (Group I: 14.5 to 15.4 m /sec and Group II:15.5 to 16.5 m/sec). Changes in the moisture content of the track cushion altered the forces exerted by the horses. Forces were lowest at 8% moisture content for Group 1 and at 12% moisture fo r Group II. Changes in the percentage of energy returned and the impac t resistance of the track also affected the forces exerted by the hors es. For the horses in Group I forces increased as energy return and im pact resistance increased. Conversely, horses in Group 11 exhibited a decrease in force as energy return and impact resistance increased. Th ese results suggest that the dynamic properties of the track may be su itable for horses traveling at relatively narrow ranges of velocity an d that when horses work at speeds outside of this range, pronounced ch anges in locomotor forces will occur.