heat

Monday, September 5, 2011

Watching Rafael Nadal suffer intense leg cramps during his press conference at the US Tennis Open is a reminder that even elite athletes are at the mercy of the elements.

Players often cramp up on the playing field but heat cramps, caused by extreme exertion in hot conditions, can have a delayed presentation. It is routine for construction workers to present with painful cramps in the large muscles that are used and abused on the job site, the abdominal wall, back, quads and hamstrings.

Air temperature is one component that puts tennis players at risk. Another is the composition and color of the tennis court surface. A dark hard baked court can retain heat and the temperature on the court may be 10 or 15 degrees hotter than that on the thermometer. All that heat radiates up and attacks the player. The same situation occurs with roofers who work on black tar surfaces where temperatures can spike to more than 120 degrees.

Heat cramps are part of the spectrum of heat related illness that also includes heat exhaustion and heat stroke. When exertion increases the internal body temperature, sweating from the skin surface is the most efficient cooling that can happen. A tennis player can lose up to 2.5 liters of sweat an hour, more than 5 pounds, and unless water and electrolytes are replaced, the body will gradually decompensate and fail to function. Initially, water is transported from within cells to the blood stream to replace the water lost in sweat. Unfortunately, this temporary maneuver can fool the thirst mechanism and prevent the athlete from drinking enough water.

Muscle cells that are dehydrated are less likely to function well and while many electrolytes are lost, it seems that it is sodium is the culprit that causes cramps. This contradicts the historic idea that low potassium was to blame. As well, the stomach can only absorb about 1.2 liters of fluid an hour or about half the potential loss. Studies show that if exercise will last more than 1 ½ to 2 hours, a balanced carbohydrate solution like Gatorade or PowerAde may be a better alternative than water and can increase water and electrolyte absorption from the stomach.

Approximately 80% of a tennis player’s energy is released as heat and cooling the body becomes a major priority. The same is true for workers who have jobs that need exertion in a hot environment. The risk for heat related illness increases towards the end of the match or as a tournament progresses since the body needs time to recover from the stress that is caused by heat exposure. Acclimating to the heat is helpful and learning how to hydrate during practice is an important prevention strategy. Unfortunately, athletes tend to drink less during matches than they do in practice. If the wet bulb globe temperature (a combination of air temperature, wind and humidity) is greater than 80F, a tennis player may have to drink more than 12 ounces of fluid every time they change sides (every two games) in a match.

In the real world, without trainers, massage therapists and coaches at our side, workers who are exposed to hot climate need to listen to their body. Heat cramps are painful but are an inconvenience. Heat exhaustion with lightheadedness, weakness, nausea and vomiting can progress to heat stroke with altered mental status, coma and death. Urine can be the guide to beating the heat. If the body is dry, the kidneys will hold onto as much water as they can and make concentrated, dark strong smelling urine. If the body is adequately hydrated, urine will come out clear.

As usual, prevention is better than treatment. Fluids replacement and stretching are the treatment of choice, but if the patient has nausea or vomiting, IV fluids may be needed to get the body back to where it wants to be. The body tolerates many stresses but lack of water is not one of them. While Mr. Nadal can defeat many opponents on the court, the pain on his face from the intense muscle cramps reminds us that even champions cannot defeat Mother Nature.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.