Heart rate response and plasma lactate concentrations of horses competing in the speed and endurance phase of 3-day combined training events.

The exercise intensity of horses competing in 3-day combined training events at 3 different levels of competition (CCI, n = 7; CCI, n = 11; CCI, n = 23) was investigated. Environmental conditions during all events were cool with 100% cloud cover. Heart rates were continuously recorded at 5 s intervals by a heart rate monitor. Mean +/- s.d. heart rate for all horses during each phase were: Phase A = 118 +/- 11 beats/min, Phase B = 179 +/- 22.7 beats/min, Phase C = 129 +/- 13.9 beats/min and Phase D = 174 +/- 19.6 beats/min. Mean +/- s.d. heart rates on Phase A and C were significantly different from mean heart rates on Phases B and D. Plasma lactate concentrations were determined at rest, within 60 s and 10 min after the end of Phase D or the cross country test. Mean +/- s.d. lactate concentrations were highest immediately post exercise (mean = 18.4 +/- 5 mmol/l for all horses) and had declined significantly in 10 min (mean = 15 +/- 6.8 mmol/l for all horses). Mean +/- s.d. heart rates and lactate concentrations were not significantly different among levels of competition at each time period. The intensity of work of fit horses successfully competing in 3-day combined training events consists of both low intensity aerobic exercise and more intense submaximal work with significant anaerobiosis. The work intensity is remarkably constant throughout different levels of competition, despite the increasing distance, number and difficulty of jumping efforts and faster optimum speeds.