Primer on Exercise Physiology

Primer on Exercise Physiology

Most horses at one time or another are used in some type of athletic endeavor.  This includes halter, endurance, racing and working horses.  Regardless of the discipline, every horse requires energy to fuel muscle activity.

Athletic performance (exercise) may be classified into three general types.  During training and/or competition horses may experience each of these alone or in combination.  These may be classified as:

  1. Speed or sprint type of activity. This is usually less than 440 yd; 1 minute in duration; and maximum exertion (VO2 max).  This type of exercise is referred to as anaerobic metabolism.  Disciplines included are Quarter Horse racing, barrel racing, timed events, and draft horse pulls.  Heart rates above 140-150 beats per minute are thought to be the anaerobic threshold.  Depending on the physical conditioning of the horse, this occurs at speeds of 11-22 miles per hour.
  2. The second type of exercise may be classified as middle distance Race distances of 0.5 to 2 miles; lasting several minutes; is 75-95% VO2 max and combines anaerobic and aerobic metabolism.  Thoroughbred and Standardbred racing are examples.  Up to a given point these horses will be performing aerobically, changing to anaerobic metabolism as time and distance increase.
  3. Endurance, often referred to as sub-maximal exercise, lasts for over 2 hours and requires aerobic energy production. Competitive and endurance riding, ranch work, farming and even show horses comprise this group.  Aerobic metabolism is the more energy efficient and allows for energy production from fats, protein, and liver and muscle glycogen.

Many disciplines require a combination of these types of metabolism while the event is taking place.  Cutting, polo, and working cow horse for example require a combination of each.  Show jumpers require middle distance and sprint type activity.  All athletic activities will utilize aerobic metabolism if only for warm-up and cool down.

Anaerobic metabolism is less efficient than aerobic metabolism both in choice of fuels and end product produced.  During anaerobic metabolism, muscle and liver glycogen, as well as circulating glucose, serve as the primary energy source.  Body stores of liver and muscle glycogen are relatively small, so depletion occurs quickly.  Another issue of anaerobic metabolism is the incomplete combustion of glycogen resulting in the accumulation of lactic acid.  Lactic acid lowers the pH in the muscle which further inhibits glycogen utilization.  The rate or speed that lactic acid accumulates relates directly to how quickly a horse slows down, an example is slowing at the end of a flat track race.  Aerobic metabolism allows dietary and body fat to be used as energy with CO2 and water being the end products.  In most horses, body stores of fat far exceed that of liver and muscle glycogen levels.  It has been suggested that a horse may produce 600 times more energy from energy sources in the body during aerobic compared to anaerobic metabolism.

Proper conditions for the chosen discipline or activity are critical to maximize the horse’s ability to succeed.  The more fit the horse, the more efficient they are in energy utilization.  In order to efficiently utilize the increased dietary energy, additional nutrients may be required.  Increased dietary vitamin E to serve as an antioxidant along with more dietary B-vitamins is often added to the ration through proper supplementation.

Breeding coupled with training, proper nutrition and LUCK all play an integral part in any athletic success.