Horses are able to increase their heart rate ten fold,
while humans can only increase their heart rate by about four times.
Cardiorespiratory fitness is the fitness of two systems which work closely together, the cardiovascular system and the respiratory system. The cardiovascular system includes the heart and blood vessels. The job of the cardiovascular system is to deliver nutrients throughout the body and remove waste products. This makes the cardiovascular system vital for both exercise and daily life. The respiratory system is the system which brings oxygen into our bodies and expels carbon dioxide. It is made up of our airways and our lungs.
You can think about cardiorespiratory exercise, also called aerobic exercise, as any exercise that increases your heart rate and elevates your breathing. Popular forms of aerobic exercise include walking, jogging, cycling, rowing, and swimming. The best form of aerobic exercise is the one you enjoy the most. Any exercise that causes pain may cause injury and will at the very least reduce exercise adherence, so it is important to find a form of exercise that you can perform without undue discomfort. It is recommended by the World Health Organization and the American Heart Association that all adults get 150 minutes of moderate intensity aerobic physical activity or 75 minutes of vigorous physical activity or a combination of both each week. An easy measure of intensity is the talk test. If you can talk but not sing during the activity, the activity is considered moderate. If you can only say a few words before pausing for a breathe, the activity is considered vigorous. Following these recommendations reduces the risk of many chronic diseases, including Type 2 diabetes, hypertension, cardiovascular disease, and colon cancer, as well as all-cause mortality. This means we can increase our years and quality of life by participating in aerobic activities and who doesn't want to be able to spend more quality time with their horses? Additionally, if you find yourself out of breath while riding your horse, chances are that your cardiorespiratory fitness is impacting your riding. If you are focused on catching your breath, you are less focused on your form as a rider and what is going on with your horse. Similarly, horses need to have aerobic exercise each week and providing that exercise positively impacts their health and longevity.
You may now be wondering how aerobic exercise provides these benefits. Well, certain adaptations occur through exercise and the effects of these adaptations can be seen not only during the performance of exercise but also at rest. These adaptations include increased stroke volume, decreased resting heart rate, and increased cardiac output. Stroke volume is the amount of blood pumped out of the heart in one contraction of the heart muscle. Trained individuals can expel more blood to the body with each contraction of the heart. Because of this increase in stroke volume, the heart can beat fewer times to deliver the same amount of blood to the body. This is why trained individuals have a lower heart rate at rest and during sub-maximal exercise. Cardiac output is a measure of the amount of blood pumped per minute. The increase in stroke volume allows a trained individual to have a higher cardiac output during sub-maximal exercise. These adaptations allow trained bodies to perform more efficiently. There are additional changes that occur in the blood of endurance trained athletes including increased mass of red blood cells and increased plasma volume. It may be noteworthy that plasma volume increases more than the mass of red blood cells, which reduces hematocrit levels. Hematocrit is the proportion of red blood cells in the blood. This phenomenon is sometimes called sports anemia. Although, the reduced hematocrit levels make an endurance athlete appear anemic, they actually have an increased number of red blood cells rather than a decrease. Their blood actually has an increase in oxygen carrying capacity. Again, there is an increased efficiency in the body of the trained individual.
These same adaptations apply to both horses and humans. The biggest difference beside the fact that horses are much larger and thus have greater blood volumes, stroke volumes, cardiac output, etc., is that they also have a much greater response to exercise. Generally, we would expect a larger animal, to have a lower heart rate. This is true of a horse's resting heart rate, which is about half that of a human's resting heart rate. But horses are able to increase their heart rate ten fold to approximately 240 beats per minute. Humans on the other hand can only increase their heart rate about four times. It also interesting to note that the heart rate of a horse is greatly affected not only by exercise but also by other stressors. More reactive horses also have more reactive heart rates. Therefore, heart rates in certain breeds like Thoroughbreds and Arabians are generally more variable than the heart rates of cold-blooded breeds such as Clydesdales and Percherons during sub-maximal exercise.
When designing an aerobic exercise program for both us and our horses, we need to remember our principles of training and how to set SMART goals. You may find my previous post on this topic helpful. Remember, that we must be specific to our goals. Training an endurance horse for a 50 mile ride will require different training than a barrel racer. Remember that all training requires a slow progression to avoid injury. As far as health goes, any aerobic activity is better than none, so get out there and do what you can.
References
Ehrman, J., Liguori, G., Magal, M., & Riebe, D. (Eds.). (2018). ACSM's guidelines for exercisetesting and prescription (10th ed.). Philadelphia, PA: Wolters Kluwer Health.
Kilpatrick, M., Lite, R., Magyari, P., & Schoffstall, J. (Eds.). (2018). ACSM's resources for the
exercise physiologist (2nd ed.). Philadelphia, PA: Wolters Kluwer Health.
Marlin, D., & Nankervis, K. (2002). Equine exercise physiology. Ames, IA: Blackwell Publishing
Professional.
