PubMed1977
The relationship of velocity (v) to heart rate (HR)and of kinetic energy (KE) to heart rate, were investigated in 6 normal horses and in 6 horses with chronic obstructive pulmonary, disease (COPD). Radiotelemetry was used to determine the heart rate while subjects were ridden on a 400m track. Velocity was measured by stop-watch between 2 markers 50 m apart at the end of the track. Kinetic energy was calculated from the formula KE =1/2 Mv2, where M = mass of horse, rider, saddle and bridle (KG) and V = velocity (metres per second). In all subjects, the relationship of velocity to heart rate was a linear one at each individual pace (i.e. walk, trot and gallop). There were however significant differences between the v/HR regression curves of each pace. These differences indicated that the increase in velocity per unit increase in heart rate was greater at the trot than at the walk, and greater at the gallop than at the trot. When data for all paces were combined, the relationship log v/log HR was a linear one. The above findings were also true of the relationship of kinetic energy to the heart rate. In horses, which reached maximal heart rate at a relatively low velocity, the v/HR curve became asymptotic. At comparable submaximal velocities, the heart rate of COPD subjects was approximately 20 beats per minute higher than that of normal subjects. This was also true when the term "kinetic energy per units mass" was substituted for velocity.