Cardiorespiratory and metabolic responses to treadmill exercise in the horse.

The research article focuses on a study observing the effects of graded treadmill exercise on the cardiorespiratory and metabolic functions in horses. The crucial findings suggest that during exercise, horses can significantly increase their aerobic metabolism by elevating hematocrit, hemoglobin, and oxygen-carrying capacity.

Study Design and Execution

• The study was conducted on five sedentary horses, where they were subjected to a five-stage treadmill test until they reached 90% of their maximum predicted heart rate.
• Various physical measurements were observed during the exercise that includes cardiac output, stroke volume, left ventricular, arterial and right atrial pressures, as well as the maximal time derivative of left ventricular pressure.
• The research also recorded changes in hematocrit (Hct), oxygen uptake (VO2), and respiratory exchange ratio (RQ) at different stages of the exercise.

Results and Findings

• The study revealed a significant increase in various measurements during the treadmill exercise and observed that the highest level of exercise led to a sixfold increase in cardiac output and a 41% elevation in stroke volume over standing values.
• Hematocrit levels, oxygen uptake, and respiratory exchange ratio also increased substantially from their initial values, reflecting a clear metabolic response during exercise.
• The researchers also noted the effect of the sympathetic stimulation of exercise, which could enhance hematocrit, hemoglobin, and oxygen-carrying capacity by emptying the spleen, leading to an increase in the total circulating red blood cells by up to 50%.

Implications of the Study

• The research implies that horses have an efficient “blood-boosting” mechanism that allows them to increase their aerobic metabolism during exercise. This mechanism enables them to elevate their hematocrit, hemoglobin, and oxygen-carrying capacity, resulting in a significant increase in their aerobic metabolism, almost 40-fold higher than the resting rate or twice the rate seen in humans.
• The findings reinforce the idea that the oxygen transport system may limit maximal aerobic capacity in humans, which is an essential consideration for athletic training and performance improvement.