Cardiorespiratory function in Thoroughbreds during locomotion on a treadmill at an incline or decline.

This research study evaluates the impact of uphill and downhill locomotion on the cardiorespiratory function of well-trained Thoroughbred horses. The study finds that downhill movement requires less energy than uphill or horizontal motion, with energy expenditure changing according to the speed of the horse.

Study Overview and Methodology

• The study was conducted using five highly trained Thoroughbred geldings.
• Exercise for the horses was carried out on a treadmill at various speeds: 1.7, 3.5, 6.0, 8.0, and 10.0 m/s. This was performed at three gradients: 4% incline, 0% incline (horizontal), and 4% decline, in a random sequence on different days.
• The researchers measured stride frequency, stride length, cardiopulmonary variables, and oxygen transport variables, analyzing these using repeated-measures ANOVA and Holm-Šidák pairwise comparisons.

Results of the Study

• The horses completed all treadmill exercises maintaining identical stride frequency and stride length.
• At the same uphill speeds, horses exhibited higher mass-specific oxygen consumption (increase by an mean of 49%) and carbon dioxide production (mean increase of 47%), cardiac output (mean increase of 21%), heart rate (mean increase of 11%), and partial pressure of carbon dioxide in the blood (Paco, mean increase of 1.7 mm Hg).
• There were decreases in the partial pressure of oxygen in the blood (Pao, mean decrease of 5.8 mm Hg) and arterial oxygen saturation (mean decrease of 1.0%) during uphill movement, with no apparent increase in tidal volume (amount of air moved into or out of the lungs during each respiratory cycle).
• Compared to horizontal motion, downhill locomotion led to lower mass-specific oxygen consumption (mean decrease of 24%), CO2 production (mean decrease of 23%), and cardiac output (mean decrease of 9%).
• The absolute energy cost during uphill movement increased linearly with speed, at around twice the rate at which it decreased during downhill movement.

Conclusions and Relevance

• From the findings, it can be asserted that for Thoroughbred horses, downhill movement incurs a lower energy cost compared to uphill or horizontal movement, and that this cost fluctuates with speed.
• The study leaves an open question on whether eccentric training (exercise that lengthens the muscle while it’s under tension, as in downhill locomotion) induces similar changes in horses’ skeletal muscle as observed in humans.