Method for quantifying net anaerobic power in exercising horses

Abstract

There is no good method for measuring net anaerobic power in exercising horses to allow accurate estimates of total metabolic power. The increase in VO2max when breathing hyperoxic (HO) gas should be accompanied by a stoichiometrically equal (in terms of ATP turnover, i.e. energy equivalents) decrease in plasma lactate accumulation rate (Mlactate). Six 3-year-old Thoroughbreds were trained on an equine treadmill wearing a semi-open flow mask for measurement of VO2. After 4 months the horses ran with reproducible specific VO2max (VO2max/kg bwt). The mask design allowed mixing of O2 or N2 with the inward bias flow of gas so that inspired O2 concentration of the horse could be controlled. While the horse breathed either HO (25.1% O2), normoxic (NO, 21% O2) or hypoxic (LO, 19.5% O2) gas, it ran at a speed sufficient to elicit VO2max in NO while jugular venous blood was drawn at 15 sec intervals over a period of 2 min to determine Mlactate. VO2max/kg bwt was not significantly different between LO and NO conditions, and LO data could not be used in the comparison. The VO2max/kg bwt increased from 2.59 +/- 0.24 (s.d.) to 2.86 +/- 0.24 mlO2 (STPD)/sec/kg in NO and HO, respectively, while Mlactate decreased from 11.5 +/- 4.2 to 9.0 +/- 3.9 mmol/min as VO2 increased. The ratio of delta Mlactate to delta VO2max/kg bwt suggests that Mlactate of approx 11.1 +/- 6.7 mmol/min is associated with net anaerobic power approximately equivalent to 1.0 mlO2 (STPD)/sec/kg of aerobic power (20.1 W/kg(-1)). The high variability in VO2max/kg bwt observed in data from some runs, particularly in LO, suggests that caution must be used when comparing data from the same horse during different runs. This study provides a tool for estimating net anaerobic power and, more accurately, evaluating total metabolic power of horses exercising at or above their aerobic capacities.