Meeting Abstract
From a dynamic perspective, terrestrial mammals of very different sizes move in a similar way as they have very similar Froude numbers, even though the dynamic properties of the tissues such as muscle do not change with the different sizes. In the present study we investigated the difference between the muscle activity patterns of the superficial gluteus medius muscle (GM) of the horse (Equus caballus) and the sheep (Ovis aries) during trotting on a treadmill. Surface electromyography and simultaneous kinematics recordings were used and stance and swing phases as well as the corresponding muscle activities were recorded. Horse and sheep showed similar overall mean activity patterns, however the phase ratio between stance and swing phase activities were 2.5 time higher in sheep then in horses. Previous work showed that toe-limit strains percentages were almost three-fold higher in equine superficial digital flexor tendons than in ovine plantaris muscles. The distortion required to make up for this could occur at the documented muscular level, as the larger mammals (i.e. the horses) stiffen their limbs more and have their muscle activity peaks later in the motion cycle than the sheep, where the earlier peak activity contributed to the muscle phase ratio difference between the species. The results of the present study show that even within the group of the ungulate mammalians differences in size and in limb design require different muscle activity patterns for an (outwardly) very similar gait such as trot; and that stance and swing phase alterations compensate for such differences.
