Blood lactate responses to submaximal field exercise tests in thoroughbredhorses

The associations between velocity during a standardized, submaximal 800-m e xercise test and blood lactate concentration after exercise were investigat ed in Thoroughbred racehorses on sand and grass racetracks. Predicted lacta te concentrations for each horse's exercise test velocity were calculated f rom the line of best fit derived from results at each racetrack. The repeat ability of the differences between the measured ed and predicted blood lact ate response to exercise was also investigated. Exercise tests were conduct ed at speeds ranging from 12.8 to 16.6 m/s. The variability of velocity wit hin the exercise test was expressed as the coefficient of variation (CV) of the times for the four 200-m sections. On the sand track, the coefficient of determination for the lactate-speed r elationship was highest for an exponential regression equation [lactate (mm ol/L) = 0.08e (0.33x) (m/s); r(2) = 0.58, P < 0.05; n = 21]. Similar coeffi cients of determination were calculated for linear (r(2) = 0.56) and second order polynomial equations (r(2) = 0.57). On the grass racetrack, the rela tionship was best described by a second older polynomial equation [lactate (mmol/L) = -0.87x(2) + 28.17x - 211.41; r(2) = 0.57, P < 0.05; n = 25]. The mean differences between the measured and predicted blood lactate concentr ations in repeated tests were 1.9 +/- 1.8 (SD) and 1.8 +/- 1.7 (SD) on the sand and grass racetracks. There were no significant associations between t he velocity of the exercise and the CV on either racetrack. Differences bet ween measured and predicted blood lactate concentrations, based on track-sp ecific lines of best fit, have potential application in field studies of fi tness in Thoroughbred horses. (C) 2000 Harcourt Publishers Ltd.