DE LA PAZ, K.L.; HOYT, D.F.; WICKLER, S.J.; COGGER, E.A.: Does Muscle Function Explain Preferred Speed?
Horses prefer to trot at speeds that are the most economical. A possible explanation for this preference is at these speeds, muscle fibers are contracting more slowly and functioning more economically. The present study was undertaken to test the hypothesis that the lateral head of the triceps, an elbow extensor, shortens less, or more slowly, at preferred trotting speed than at those speeds above and below preferred trotting speed. Muscle length changes were measured using sonomicrometry and analyzed during the portion of stance phase when EMGs indicated the muscle was active and during which time there was an extensor moment at the elbow. Three Arabian horses (4-7 years old) were trotted at speeds from 2.5-4.5 m/s. Total positive strain (muscle shortening) and average positive strain rate (velocity of muscle shortening) were calculated at each speed. Total positive strain averaged 12% and showed no significant relationship with speed (R2=0.01, P>0.05). There was a positive linear relationship between speed and average positive strain rate in two of the three horses studied (R2=0.64 and 0.87, P<0.05). This increase in average positive strain rate resulted from a decreased time of contact. These observations are inconsistent with the proposed hypothesis. Supported by NIH 1 S06 GM53933.
