Effects of treadmill elevation on heart rate, blood lactate concentration and packed cell volume during graded submaximal exercise in ponies.

Six ponies performed a standardised exercise test on a motorised treadmill at each of three randomly assigned treadmill elevations (1, 4, or 7 degrees). The exercise test consisted of four, 4 min increments of increasing treadmill speed from 1.0 to 3.4 m/sec. Heart rate, blood lactate concentration, and packed cell volume (PCV) were determined, during the last min of each exercise level, and at 4 and 12 mins post exercise. Regardless of treadmill elevation, no differences were observed in pre-exercise heart rate (49 +/- 2) beats/min), lactate (1.2 +/- 0.1 mM), and PCV (0.32 +/- 0.01 litres. During exercise, heart rate and PCV were highly correlated to treadmill speed and elevation. Peak exercise heart rates (determined at 3.4 m/sec) were 159 +/- 10, 182 +/- 5, and 216 +/- 6 beats/min at 1, 4, and 7 degrees, respectively, while peak PCVs were 0.37 +/- 0.01, 0.40 +/- 0.01 and 0.42 +/- 0.02 lit/litre at 1, 4, and 7 degrees, respectively. Blood lactate did not change significantly from pre-exercise levels during the exercise test at a treadmill elevation equal to 1 degree, but increased markedly at 4 and 7 degrees. Peak lactates were 1.9 +/- 0.7, 5.3 +/- 1.0, and 18.1 +/- 1.5 mM at 1, 4, and 7 degrees, respectively. There was a highly significant correlation between heart rate and lactate at all treadmill speeds and elevations. Therefore, during graded, submaximal exercise increasing treadmill elevation up to 7 degrees results in increases in heart rate, blood lactate concentration and PCV comparable to those seen with increasing treadmill speed alone.