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Muscle Cramps


It’s hot and maybe humid. The game, match, practice or race has been going on for some time and the athlete has been working hard and is getting tired. The athlete is drinking large amounts of fluid to combat his profuse sweating but then all of a sudden, he is struck with debilitating muscle cramps and can no longer compete and may even require medical attention. What happened? And more importantly, why does this only happen some of the time with this athlete and not to other athletes?

Insufficient conditioning and fatigue can cause muscle cramps but passive stretching, icing and massage can often resolve them. Such is not the case for muscle cramps that happen in the heat. These, termed heat cramps, will be the main focus of this article and are usually the cause of salt loss and dehydration.

What Causes Heat Cramps?

Heat cramps often occur during prolonged training when there has been profuse and repeated sweating, such as in football, a triathlon, or a tennis tournament. Large losses of fluid and sodium can be factors that predispose athletes to heat cramps. Because sodium plays an important role in initiating signals from nerves and actions that lead to movement of the muscles, a deficit could short-circuit the coordination of nerves and muscles. This could result in selected motor nerve endings becoming hyperexcitable resulting in spontaneous muscle contractions or cramping.

Sweat Loss

In warm to hot conditions, adult athletes can lose one to two and a half liters of sweat per hour. During a longer race or competition, it would not be unheard of for an athlete to lose as much as 10 liters! How much an athlete will lose depends on many factors including temperature, humidity, solar radiation, intensity of exercise, heat acclimatization status and fitness level. An increase in any one of these tends to increase sweating in the athlete.

Sweat is mostly comprised of water but also contains the minerals sodium, chloride, potassium, calcium and magnesium. However, the amounts of potassium, calcium and magnesium are very low compared to the amounts of sodium and chloride. These minerals are also easily replaced by the diet and the muscles tend to hoard them more than sodium and chloride.

Sodium Loss

How much sodium can an athlete lose in a training session or game? Well-conditioned athletes who are fully acclimatized to the heat often have sodium losses of 115-690 milligrams per liter of sweat. These same athletes who are not acclimatized to the heat can have sodium losses of 920-2300 milligrams per liter of sweat. And as sweat rates go up, so does the loss of sodium. It is common for a heavy sweater to lose 2500-5000 milligrams of sodium per hour in a hot environment. Over an extended training session or game, this could translate into a 15 to 30 percent deficit in the total body exchangeable sodium!

What about the athlete who is salt-sensitive or conscious or follows a low salt diet (defined as less than 2500 milligrams per day)? This athlete is even more susceptible to heat cramps, especially if it is a hot and humid environment, because they start with lower sodium stores before suiting up.

Preventing Heat Cramps During Training or Competition

Since the athlete is losing large amounts of fluid and sodium, it only makes sense to replace these two during training. Consuming a sports drink that contains a minimum of 110 milligrams of sodium per eight ounces is the best strategy to try to ward off heat cramps during exercise. Because of the high sweat rates of some athletes, sports drinks should be offered and readily available at all practices, games and races. In addition, the athlete must be encouraged to drink often. Some athletes tend to forget to hydrate until it is too late. That is, when they have lost at least two percent of their body weight and their performance is suffering.

The key is to encourage the athlete to drink six to 12 ounces of sports drink every 15 to 20 minutes. This will help keep the athlete hydrated and replace the sodium that they are losing in sweat. With very “salty” sweaters, for athletes who have a high sweat rate, or for longer competitions in a hot and humid environment, more sodium and fluid may be needed. For cramp-prone athletes, extra salt intake in their daily diet and during training or competition is a necessity and can be easily taken care of by adding ¼ teaspoon of salt to a 16 to 20 ounce beverage.

And forget the old practices of using pickle juice, mustard packets, and antacids as sources of sodium. These often have too much sodium and to little fluid.

Rehydrating After Training or Competition

It will be close to impossible to keep up with heavy sweat losses during training or competition. The goal is to try to replace the lost sodium and fluid as much as possible to prevent a negative impact on performance. That said, fluid and sodium intake post-training or competition is just as important, if not more important, than during the event. The reason is because the athlete will undoubtedly be training soon thereafter and it is crucial for their body to be rehydrated and sodium stores to be high again.

For an athlete to completely rehydrate after training or competition, he must consume more fluid than what was lost through sweat because some fluid continues to be lost through urine during the rehydration period. It is recommended that the athlete replace 150 percent of his sweat losses. Drinking 24 ounces for each pound lost is recommended. Before the next training session or practice, the athlete should replace 80 percent of weight lost. While specific sodium guidelines do not exist, it is important to include sodium in the rehydration process because sodium helps to facilitate glucose and water entry into the body’s cells. Pure water or a beverage lacking sodium should never be used for rehydration.

Preventing heat cramps begins with replacing fluid and sodium losses during and after training or competition. For salty sweaters or if an athlete is expected to have a higher sweat rate, additional sodium is required in their beverages and their daily diet.

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