Effects of three warm-up regimens of equal distance on V o₂ kinetics during supramaximal exercise in Thoroughbred horses

Reasons for performing study: Several studies have indicated that even low-intensity warm-up increases V̇O_2max transport kinetics and that high-intensity warm-up may not be needed in horses. However, conventional warm-up exercise for Thoroughbred races is more intense than those utilised in previous studies of equine warm-up responses.Objectives: To test the hypothesis that warm-up exercise at different intensities alters the kinetics and total contribution of aerobic power to total metabolic power in subsequent supramaximal (sprint) exercise in Thoroughbred horses. Methods: Nine well-trained Thoroughbreds ran until fatigue at 115% of maximal oxygen consumption (V̇O_2max) 10 min after warming-up under each of 3 protocols of equal running distance: 400 s at 30% V̇O_2max (LoWU), 200 s at 60% V̇O_2max (MoWU) and 120 s at 100% V̇O_2max (HiWU). Variables measured during exercise were rates of O₂ and CO₂ consumption/production (V̇O₂,V̇O_CO2), respiratory exchange ratio (RER), heart rate, blood lactate concentration and accumulation rate and blood gas variables. Results: V̇O_2max was significantly higher in HiWU than in LoWU at the onset of the sprint exercise and HR was significantly higher in HiWU than in LoWU throughout the sprint. Accumulation of blood lactate, RER, P_aco₂ and Pv̄_CO2 in the first 60 s were significantly lower in HiWU than in LoWU and MoWU. There were no significant differences in stroke volume, run time or arterial-mixed venous O₂ concentration.Conclusions: These results suggest HiWU accelerates kinetics and reduces reliance on net anaerobic power compared with LoWU at the onset of the subsequent sprint.