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Hydration, heat, nutrition for endurance events

This is an excerpt from Track & Field Coaching Essentials by USA Track & Field.

Safety in the Endurance Events

Good safety practices should be used when training endurance athletes. Because of the high volume of work, special problems arise. A proper training program balances intensity and volume and provides event-specific flexibility, strength, and drill training. Coaches should give thought to the training surface and appropriate footwear for the athletes given the conditions.

Because most endurance training programs include a great deal of training off the track, safety when running near traffic and other hazards is an important consideration. Overtraining and heat-related problems are significant issues in these events; avoiding these situations is an important part of safety and injury prevention. Hydration, environmental conditions, and nutrition are also more significant in the endurance events because of their longer duration.

Dehydration

Dehydration thickens the blood and makes it harder to pump (think water versus molasses). On average, males can lose 2.0 liters (or quarts) per hour through sweating; females, 1.1 liters per hour. In warm weather athletes should restrict their fluid loss to 1 to 2 percent of their total body weight. Each pound (about 0.5 kg) of fluid loss needs to be replaced by 16 to 24 ounces (473 to 710 ml) of water. Runners should consume 16 to 24 ounces (473 to 710 ml) of fluid containing electrolytes per pound (about 0.5 kg) of body weight lost during exercise. These figures are estimates; there is great variability among individuals and environmental conditions. In addition, for optimal performance for events lasting longer than one hour, athletes should consume 120 to 400 calories per hour during the event either as fluids or in addition to fluids.

Heat

Performance in endurance events can be significantly affected by extremes in climate. In regard to heat, the longer the event, the greater the impact. In the case of the marathon, for every 5 degrees the temperature rises above 50 degrees Fahrenheit (or about 3 degrees it rises above 10 °C), the athlete's final time typically increases by about 0.5 percent. If the temperature is above 98.6 degrees Fahrenheit (37 °C) and the humidity is above 70 percent, running outside should be avoided. The body sheds heat through the evaporation of sweat. When humidity is high, evaporative cooling is inhibited, and so is the body's ability to shed heat.

Great care needs to be taken when an athlete travels from a cooler climate to a warmer climate or when the daily temperature rises significantly. The body takes 5 to 8 days to significantly acclimatize to warmer conditions, and 14 days to reach near-maximal acclimatization.

Heatstroke is a medical emergency and should be treated immediately by getting the runner into an air-conditioned, or at least cooler and shaded, environment. Attempts to bring down the athlete's body temperature through the use of water and ice should begin immediately while medical assistance is sought.

Iron

Inadequate body iron reserves affect the athlete's adaptation to training. Low iron limits the quality and quantity of high-level endurance work output. Fitness is built by the athlete adapting to the training stimulus, and this adaptation requires iron.

Iron deficiency, which is more common in female athletes, can cause overtraining symptoms. A decrease in iron stores can cause a decrease in aerobic capacity since iron is part of hemoglobin, which carries 98.5 percent of blood's oxygen, and more than half of the enzymes of aerobic metabolism contain iron.

Excessive impact stress can cause hemolysis due to extravascular compression and intravascular acidosis, which can cause the following to occur:

• Increase in blood acidity
• Increase in red blood cell transit velocity
• Decrease of the mean life of red blood cells from a normal 120 days to approximately 80 days

Iron depletion is a decrease in serum ferritin levels, which inhibits erythrocyte and hemoglobin levels in the blood. An athlete's ferritin level is the most accurate indicator of his or her iron stores. Distance athletes who run 60 miles or more per week should have their ferritin levels monitored at least twice a year. If blood tests reveal an iron deficiency, the athlete should reduce training volume and consult a sport science doctor or nutritionist to begin a program designed to increase iron stores through good nutrition and iron supplementation.

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