Assessment of two methods to determine the relative contributions of the aerobic and anaerobic energy systems in racehorses

Abstract

A prospective, randomized, controlled study was designed to determine relative aerobic and anaerobic (lactic and alactic) contributions at supramaximal exercise intensities using two different methods. Thoroughbred racehorses (<i>n</i> = 5) performed a maximal rate of oxygen consumption (V̇o_2max) test and three supramaximal treadmill runs (105, 115, and 125% V̇o_2max). Blood lactate concentration (BL) was measured at rest, every 15 s during runs, and 2, 5, 10, 20, 30, 40, 50, and 60 min postexercise. In <i>method 1</i>, oxygen demand was calculated for each supramaximal intensity based on the V̇o_2max test, and relative aerobic and anaerobic contributions were calculated from measured V̇o₂ and the accumulated oxygen deficit. In <i>method 2</i>, aerobic contribution was calculated using the trapezoidal method to determine V̇o₂ during exercise. A monoexponential model was fitted to the postexercise V̇o₂ curve. Alactic contribution was calculated using the coefficients of this model. Lactate anaerobic contribution was calculated by multiplying the peak to resting change in BL by 3. Linear mixed-effects models were used to examine the effects of exercise intensity and method (as fixed effects) on measured outcomes (<i>P</i> ≤ 0.05). Relative aerobic and anaerobic contributions were not different between methods (<i>P</i> = 0.20). Horses' mean contributions were 81.4, 77.6, and 72.5% (aerobic), and 18.5, 22.3, and 27.4% (anaerobic) at 105, 115, and 125% V̇o_2max, respectively. Individual alactic anaerobic energy was not different between supramaximal exercise intensities (<i>P</i> = 0.43) and was negligible, contributing a mean of 0.11% of the total energy. Relative energy contributions can be calculated using measured V̇o₂ and BL in situations where the exercise intensity is unknown. Understanding relative metabolic demands could help develop tailored training programs. <b>NEW & NOTEWORTHY</b> Relative energy contributions of horses can be calculated using measured V̇o₂ and BL in situations where the exercise intensity is unknown. Horses' mean contributions were 81.4, 77.6, and 72.5% (aerobic), and 18.5, 22.3, and 27.4% (anaerobic) at 105, 115, and 125% of V̇o_2max, respectively. Individual alactic capacity was unaltered between supramaximal exercise intensities and accounted for a mean contribution of 0.11% of energy use.