Hydration and Physical Performance

Abstract

There is a rich scientific literature regarding hydration status and physical function that began in the late 1800s, although the relationship was likely apparent centuries before that. A decrease in body water from normal levels (often referred to as dehydration or hypohydration) provokes changes in cardiovascular, thermoregulatory, metabolic, and central nervous function that become increasingly greater as dehydration worsens. Similarly, performance impairment often reported with modest dehydration (e.g., −2% body mass) is also exacerbated by greater fluid loss. Dehydration during physical activity in the heat provokes greater performance decrements than similar activity in cooler conditions, a difference thought to be due, at least in part, to greater cardiovascular and thermoregulatory strain associated with heat exposure. There is little doubt that performance during prolonged, continuous exercise in the heat is impaired by levels of dehydration ≥ −2% body mass, and there is some evidence that lower levels of dehydration can also impair performance even during relatively short-duration, intermittent exercise. Although additional research is needed to more fully understand low-level dehydration's effects on physical performance, one can generalize that when performance is at stake, it is better to be well-hydrated than dehydrated. This generalization holds true in the occupational, military, and sports settings.

• hydration
• dehydration
• hyperhydration
• performance
• physical activity

Key teaching points:

• Dehydration during physical activity is commonplace because voluntary fluid intake is often less than fluid loss through sweating.

• Dehydration results in unavoidable, negative effects on physiological function and exercise performance. The magnitude of the effects of dehydration is exacerbated by increases in heat stress, exercise duration, and exercise intensity.

• Adequate drinking during exercise helps attenuate the reductions in blood volume, cardiac output, muscle blood flow, skin blood flow, the rise in core temperature, and the impairment in exercise performance that accompany dehydration.

Key teaching points:

• Dehydration during physical activity is commonplace because voluntary fluid intake is often less than fluid loss through sweating.

• Dehydration results in unavoidable, negative effects on physiological function and exercise performance. The magnitude of the effects of dehydration is exacerbated by increases in heat stress, exercise duration, and exercise intensity.

• Adequate drinking during exercise helps attenuate the reductions in blood volume, cardiac output, muscle blood flow, skin blood flow, the rise in core temperature, and the impairment in exercise performance that accompany dehydration.

Notes

Conflict of interest disclosure: Dr. Murray is the director of the Gatorade Sports Science Institute and is an employee of The Gatorade Company, a wholly owned subsidiary of PepsiCo. Gatorade produces and markets hydration and sports nutrition products to athletes and physically active consumers.

Presented at the ILSI North America 2006 Conference on Hydration and Health Promotion, November 29–30, 2006 in Washington, DC.