Kentucky Equine Research

Challenges of Endurance Exercise: Water and Electrolyte Depletion

April 26, 2010

Hal Schott, D.V.M, Ph.D., a professor at Michigan State University, spoke next. His talk, titled "Challenges of Endurance Exercise: Water and Electrolyte Depletion," discussed the most popular endurance trials in the horse world, primarily endurance rides and the speed and endurance phase of three-day events, and the performance problems associated with hydration and electrolyte balance.

He discussed the role of dehydration on performance and in the development of metabolic problems and exhaustion. A syndrome known as "involuntary dehydration" is quite common among endurance athletes and results in a significant change in body mass. Involuntary dehydration can be defined as a condition in which body fluid losses are only partially replaced by drinking during and shortly after the exercise bout.

Schott then discussed ailments that affect human endurance athletes such as hyperthermia and hyponatremia. Hyperthermia is not often documented in horses. Hyponatremia, a well-documented condition in humans that causes nausea, pulmonary edema, and neurological deficits, has not yet been recognized as a problem among equine endurance athletes.

Dehydration among endurance exercise is unavoidable. An average of 5% body weight loss is expected during endurance exercise. This contrasts with humans, who often lose 2-3% of body weight. Most body weight is lost during the early stages of the ride.

Schott explained "exhausted horse syndrome," a consequence of dehydration due to prolonged sweating during an exercise bout. This syndrome is characterized by synchronous diaphragmatic flutter (thumps), muscle fasciculations, colic pain associated with ileus, rhabdomyolysis, collapse, neurological deficits, and multiple organ failure. Horses often have rapid recovery with administration of relatively small amounts of intravenous fluids.

Failure of horses to eat drink is likely an important warning signs for impending problems during a ride. Limiting dehydration is paramount. While forced drinking is not practical, proper nutritional management of horses leading up to and during a ride is critical.

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