• horse;
  • aerobic;
  • anaerobic;
  • oxygen uptake kinetics;
  • oxygen deficit;
  • energy partitioning


The V̇O2max in racehorses is approximately double that of elite human athletes and the rate of increase in V̇O2 at the onset of high intensity exercise is much greater than in man. The kinetics of gas exchange are affected by a warm-up prior to exercise in humans, there being a greater aerobic contribution to high intensity exercise after warm-up. Our hypothesis was that a warm-up would increase aerobic energy delivery in racehorses during high intensity exercise. Thirteen fit Standardbred racehorses ran to fatigue at 115% of V̇O2max on a treadmill at 10% slope. Prior to acceleration, horses were exercised either for 5 min at 50%V̇O2max followed by 5 min walk, or walked for 2 min. Samples of expired gas were collected every 10 s during the run for determination of V̇O2 and V̇CO2 and measurement of maximal accumulated oxygen deficit (MAOD). Blood lactate concentration was measured 5 min post exercise. We found that with a warm-up, horses had faster kinetics of gas exchange and a greater proportion of their total energy requirement was supplied by aerobic sources. The aerobic contribution to total energy requirement with and without warm-up was, respectively, 79.3 ± 1.0% and 72.4 ± 1.7% (P<0.01). There was also a higher MAOD (P< 0.01) in horses that had not been given a warm-up (mean ± s.e.m. 34.7 ± 2.6 and 47.3 ± 2.6 ml O2 eq/kg bwt with and without a warm-up respectively). However, there were no significant differences in total run time or estimated total energy expenditure between the 2 protocols. We concluded that during high intensity exercise to fatigue lasting 1 to 2 min, more than 70% of energy supply is from aerobic energy sources and that this contribution is even greater when the horses have received a warm-up.