Training-induced modifications in cardiorespiratory and ventilatory measurements in thoroughbred horses

The effects of training and detraining on ventilation during a standardised exercise test were investigated. Ten healthy Thoroughbred horses underwent 5 standardised treadmill exercise tests (SET): SET1, at the start of the experimental period; SET2, after 3 weeks acclimatisation; SET3, after 3 week of aerobic training; SET4 after 3 weeks of anaerobic (i.e. interval) training; and SET5, after 3 weeks of detraining. The SETs were carried out in an air-conditioned laboratory on a treadmill inclined at 6 degrees. Respiratory airflow, tidal volume (VT), respiratory frequency (RF) and expired minute volume (VE) were obtained using a face mask and 2 ultrasonic pneumotachographs. Peak oxygen uptake (VO2 peak) and carbon dioxide production (VCO2 peak) values were calculated on a breath-by-breath basis, using a mass spectrometer. Heart rate (HR) was continuously measured with a polar horse tester. Oxygen pulse (VO2/HR) and ventilatory equivalent for O2 were calculated from the collected data. Venous blood was sampled before and after the SET for lactate, pH and haemoglobin determinations. The results indicated that trained horses showed significant modifications of all values, except VT, RF and VE. This study suggests that, in horses, the increase in VO2 induced by training seems to be mainly due to cardiovascular and haematological changes rather than to ventilatory changes. Consequently, while all the other systems implicated in exercise physiology can be efficiently improved and trained, the ventilatory capacity has only limited ability to adapt to training.