Effects of two field continuous incremental tests on cardiorespiratory responses in Standardbred trotters

{In humans, cardiorespiratory responses are widely evaluated from field incremental exercise tests. On the contrary, equine exercise physiology faces a huge lack of oxygen consumption measurements (VO2) in field conditions due to technical concerns. The aim of this study was to test the effects of two incremental continuous field tests on cardiorespiratory responses in Standardbred trotters. The two protocols were realized at trot and ended when horses galloped. The tests started at 4.2 m/s (T1) and 6.4 m/s (T2), with speed increments of 1.4 m/s every 3 min for T1 and 0.8 m/s every 2 min for T2. Velocity (v), heart rate (HR) and gas exchanges were recorded continuously, and blood lactate concentration [La-] was measured before and after tests. Values recorded at the end of the tests were considered as peak values. The v(peak) values were 10.6 +/- 0.3 and 10.7 +/- 0.7 m/s for T1 and T2 respectively. Horses reached higher VO2peak (T1: 116.6 +/- 11.5 ml/min/kg; T2: 88.9 +/- 10.2 ml/min/kg; p < 0.05) and HRpeak (T1: 217 +/- 5 bpm; T2: 209 +/- 3 bpm; p < 0.05) during T1 compared with T2. T1 was significantly longer than T2 (17.5 +/- 1.9 vs. 12.9 +/- 1.6 min respectively, p < 0.01), and the number of steps entirely ran tended to be different (T1: 5.6 +/- 0.6; T2: 6.2 +/- 0.8