Evaluation of oxygen consumption during field exercise tests in Standardbred trotters

Reasons for performing the study: In human exercise physiology, the current gold standard for evaluating aerobic capacity is the measurement of oxygen consumption (VO2max) and maximal oxygen uptake (VO2max). The evaluation of VO2, in horses is performed in some laboratories equipped with a treadmill but has only been exceptionally reported in field conditions because of the lack of adapted equipment. Objectives: The aim of this study was (1) to assess the feasibility of VO2 measurement on the track using a recently validated portable breath-by-breath gas analyser system adapted to horses (Cosmed K4b® and Equimask®), (2) to compare these results with those obtained during a treadmill exercise test and (3) to study correlations between VO2 and physiological parameters usually measured in field condition such as heart rate (HR), lactataemia (LA) and the speed at which HR equals 200 beats per minute (bpm) (V200) or LA 4 mmol-1 (VLA4). Methods: Five healthy Standardbred trotters in training were submitted to two stepwise incremental exercise tests, one driven on the racetrack and the other on a high-speed treadmill with a 4% incline. Speed (v), HR, ventilatory parameters and VO2 were continu¬ously recorded throughout the duration of the tests and LA was evaluated after each step. Results: All horses com¬pleted the test satisfactorily after an initial acclimatization to the mask. There were marked individual differences in ventilatory strategy, and breathing frequency (Rf) at the higher levels of exercise was noticeably low. The VCO2 measurements were incoherent. There were no significant differences between track and treadmill maximal data obtained during the last stop [VO2peak (track: 139.9 ± 8.9 ml kg-1min-1; treadmill: 139.9 ± 13.4 ml kg-1min-1), LAmax (track: 6.5 ± 1.6mmol-1; treadmill: 7.3 ± 3.Ommol-1-1), HRma (track: 229 ± 6.2 bpm; treadmill:222 ± 13 bpm)], although the maximal speed required to reach similar workloads was significantly higher on the track (11.9 ± 0.6 ms-1 vs. 9.7 ± 0.4 ms-1). The correlation between VO, and HR (r= 0.87; P < 0.001) and VO2 and LA (r = 0.75; P < 0,001) during both tests was good but no correlation was found between VO2peak and HRmax, LAmax, V200 or VLA4. Conclusions: This is the first report of a practical portable system to measure VO2 and ventilation continuously during high-speed field exercise tests. However, current mask design markedly influences ventilation and could have prohibited the attainment of VO2max Furthermore, consistent VCO2 measurements should be implemented by the manufacturers. Potential relevance: Continuous breath-by-breath ventilation and VO2 measurements can be recorded in horses in the field at submaximal levels. With necessary adaptations to the system entailed, this study opens new perspectives in the analysis of physiological and metabolic mechanisms of exercise in the equine species in genuine track conditions.