EFFECT OF TREADMILL INCLINE AND SPEED ON METABOLIC-RATE DURING EXERCISE IN THOROUGHBRED HORSES

We examined the effect of treadmill speed and incline on O-2 uptake (V O2), CO2 production, heart rate (HR), plasma lactate concentration, ec onomy of locomotion, stride frequency, and stride length. A further ai m was to examine the relationships between HR and VO2 and lactate and VO2 and whether these relationships vary with alterations in treadmill incline. The experiment was a latin square design, using five horses and five treadmill inclines (0, 2.5, 5.0, 7.5, and 10.0%). Fit Thoroug hbred horses exercised for 4 min at 3 m/s at 0% slope, after which the treadmill was set to the allocated incline. Speeds tested ranged from 1 to 13 m/s. The relationships of VO2 and CO2 production with speed w ere curvilinear at 0 and 2.5% and linear at 5, 7.5, and 10% inclines. There was a linear relationship of HR and speed with a significant eff ect of incline. The plasma lactate concentration increased exponential ly with speed, and there was a significant effect of incline. Stride l ength increased linearly and stride frequency increased in a curviline ar manner with speed but there was no effect of incline. There were li near relationships of HR with VO2 and HR with VO2 when expressed as pe rcentage of maximum VO2 and maximum HR that were not affected by incli ne. The O-2 cost of exercise on a 10% incline was similar to 2.5 times that for exercise on the flat. The strong relationship between the pr ecentages of maximum HR and maximum VO2 indicates that over a wide ran ge of exercise intensities the relative VO2 can be accurately predicte d from measurements of HR.