STRIDE LENGTH AND RESPIRATORY TIDAL VOLUME IN EXERCISING THOROUGHBREDHORSES

The purpose of this study was to test the hypothesis that locomotor-re spiratory coupling in horses may provide a basis for the appropriate m atching of lung ventilation to running speed and metabolic power. This was achieved by determining the effect on respiratory frequency and t idal volume in thoroughbred horses of changing running speed while mai ntaining a constant metabolic demand by also varying the incline of th e treadmill. This procedure was performed at three different speeds at two different levels of metabolic rate. It appears that, in response to metabolic demands which are not directly related to speed, horses c an control tidal volume independently of stride length but they do not vary respiratory frequency independently of stride frequency. When ru nning at 0-degrees incline, however, they probably do not operate an e levated tidal volume, because of the increased energetic costs such an elevated tidal volume would incur.