Experienced athletes generally have no trouble properly hydrating while exercising or training.  In fact, most athletes are aware of the role hydration plays in their performance and will take all measures to insure proper hydration before, during and after activity including acclimating to the environment in which they will be competing.  However, many clients and beginning athletes are unaware of the dangers lurking outdoors in the elements.

Heat adaptation

It is well-known that exercising in a hot environment accelerates muscle fatigue, challenging the body to regulate its core temperature and dissipate heat. However, did you know that as the core temperature rises, a change in muscle metabolism takes place?  Oxygen uptake, heart rates and blood lactate concentrations increase during exercise in the heat.  In addition, muscle glycogen utilization per hour is significantly in hot conditions.

An acute episode of hyperthermia starts off relatively mildly with symptoms like headache and nausea. If activity continues and hydration and temperature regulation are not addressed, symptoms can progress to cramps, heat exhaustion (with dizziness, profuse sweating and weak/rapid pulse), and ultimately heat stroke which can cause a loss of consciousness or even in extreme instances, death.

When exercising intensely for prolonged periods and/or in hot, humid conditions, keeping a watchful eye on hydration is crucial for optimal performance and health. Steps in preventing dehydration or heat stroke include

• Adequate fluid intake before and throughout practice or competition
• Monitoring of heart rate (any significant change in HR to constant activity shows a poor response to the demands of that activity)
• Monitoring of weight, replacing weight losses with fluid. Remember, a pint weighs a pound

Fortunately, continued exposure to training in warm environments leads to adaptations that make it easier to perform in the heat. These adaptations include an increased capacity to sweat, reduced salt losses in sweat and a lower body temperature and heart rate response during activity. Excitingly, these adaptations can take place in a little as 7-14 days.

The primary mechanism for the body’s heat loss at high levels of work in both normal and hot environments is the evaporation of sweat which releases heat from the body. Sweat rates increase linearly with increased exercise intensity, and in hot weather sweat losses can reach close to 3.0 liters/hr.  

Fluids and performance

Without proper hydration, athletes cannot reach peak performance, even if exercise is only a few minutes long. The longer an athlete remains with inadequate hydration, the less desirable performance they will exhibit.  

Among US high school athletes, heat illness is the third leading cause of death. It doesn’t help that many distance running races, triathlons and football games occur in warmer times of the year.

Many athletes and exercisers mistakenly think that their thirst will guide them to ideal hydration. Thirst typically occurs when the one’s water deficit is approximately two percent of body mass. Performance begins to be impaired with a fluid loss of as little as 1%, suggesting our natural thirst mechanisms cannot keep up with exercise-induced fluid losses. In other words, by the time we register we are thirsty, performance may be in decline.

How can performance be affected by such small fluid deficits? It may be due in part to the decrease in plasma volume (any decrease in fluids will automatically decrease blood/plasma levels), impairing the delivery of oxygen and nutrients in and out of muscles. Along with the loss of fluids, especially during prolonged exercise and profuse sweating, we also lose electrolytes that are involved in muscle and nerve function. In addition, prolonged exercise can create a significant decrease in muscle and liver glycogen, the body’s main energy sources. Replacing fluid, electrolytes and glucose is the formula for performance success, especially in longer duration exercise (more than 60 minutes) in hot environments.

Children and Older Exercisers/Athletes

In young children, adolescents and in older (40+) athletes, we find natural hydration mechanisms (thirst triggers, taste) and heat dissipation functions (skin blood flow and sweat rates) are underdeveloped or diminished, making proper hydration strategies a bigger concern. In these populations monitoring is generally required.  Follow the hydration guidelines below to keep your athletes at peak performance levels before, during and after the game or exercise session.

Hydration Guidelines

Pre-workout Guidelines	During Exercise	Post workout Guidelines
Drink approximately 16 ounces of fluid two hours before activity, and an additional 8-16 ounces 30-60 minutes prior to training on warm and/or humid days. Water may be adequate for activities lasting less than an hour. If you are participating in endurance events, repeated bouts of exercise greater than 60 minutes, or multiple practices a day, use a sports drink containing 6-8% carbohydrate.	Depending on your sport, consume 6-12 ounces of water or sports drink every 15-20 minutes. This equates to approximately 32 ounces per hour. For prolonged exercise greater than four hours, choose a sports drink with small amounts of electrolytes.	Immediately following activity, consume at least 16 ounces of fluid for every pound of weight lost to ensure proper rehydration. A liquid shake with high carbohydrate content, minimal protein and fat can maximize recovery if muscle glycogen levels have been depleted. Drink an additional 16 ounces with your post-workout snack and/or meal. Weigh yourself each morning. A stable weight generally indicates proper fluid balance.

 

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Tags: dehydration, fluids, Nutrition, proper hydration

This entry was posted on Thursday, March 11th, 2010 at 12:55 pm and is filed under Nutrition. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.