Douglas W. Stoddard, MD, MSport Med
For as long as athletes and hot-weather activities have been around, muscle cramping has been a familiar complaint. Based on my experience tending to athletes suffering from heat-related illnesses, the incidence of cramping in hot endurance sports is increasing.
For as long as athletes and hot-weather activities have been around, muscle cramping has been a familiar complaint. Based on my experience tending to athletes suffering from heat-related illnesses, the incidence of cramping in hot endurance sports is increasing. A probable reason is the greater length of athletic events coupled with the hotter temperatures we’ve had in recent years.
Cramping typically occurs in the muscles used the most. For example, tennis players can experience cramping in their forearms. Runners cramp in their calves and cyclists in their quadriceps. Triathletes usually get nailed in both quads and calves and the cramping typically hits during the run portion of the event when fatigue and other physiological disturbances are at the peak.
The most established theory of cramping relates to electrolyte disturbances. These occur due to sweating. The electrolytes mentioned most are dependant on sodium and potassium. Normal levels of both of these ions are crucial for neuromuscular function. Some relevant "sweat facts" are as follows:
You probably don’t drink a litre of fluid per hour. If you do, you may be drinking liquid that’s not supplying enough electrolytes. This is especially true of water. It’s also a problem with most sports drinks, and therein lies the problem. The numbers tell the story of how easy it is to drop your sodium and potassium levels with prolonged sweating. This is not helped by a low rehydration rate and the low electrolyte levels in your drink.
While sodium and potassium are likely the most important electrolyte ions, calcium, zinc and magnesium ions are also worth considering, as there are many anecdotal reports of how supplementing with these minerals has helped cramping.
Other important factors to consider are: dehydration from large volumes of water lost in sweat; lactic acidosis (lactic acid buildup) resulting from working close to or at your anaerobic/lactate threshold; and hypoglycemia (low blood sugar or "hitting the wall"), resulting from inadequate replacement of easily absorbed carbohydrates.
The Right Electrolytes
Prevention is a fourfold proposition. It’s accomplished by a properly formulated sports drink that reduces electrolyte depletion. The ratio of sodium to potassium in sweat is from three to five parts sodium to one part potassium. The ratio in the drink should be about the same. Some have more potassium than sodium in them. The addition of zinc, magnesium and calcium may also be beneficial. (Salt tablets are an inexact way of replenishing lost sodium and typically do not contain other electrolytes.)
To prevent dehydration–drink! If you lose a litre of sweat per hour, you must put back this amount. Weighing yourself before and after your event will give you an idea of how much water loss you have experienced. Remember, one litre of fluid is equal to one kilogram (or 2.2 pounds).
To reduce lactic acid accumulation, use a sports drink that contains a lactic acid buffer. Not many do. Excellent buffers convert in your body to bicarbonate, one of the most important substances in the body for buffering lactic acid. (Bicarbonate itself is irritating to the gastrointestinal tract.)
To reduce hypoglycemia, use a sports drink that has easily absorbed and readily usable carbohydrates. Simple sugars like glucose or dextrose are best. Dextrose is great for this (in fact, dextrose is the sugar used in intravenous fluids when rapid sugar replacement is required). Dextrose easily passes through your gut wall into the blood stream and requires no processing by your liver before your muscles can use it. It doesn’t irritate your gut and isn’t too sweet.
Beware of sports drinks that contain fructose–fructose is fruit sugar. It’s very sweet, can cause gastrointestinal irritation and requires processing by your liver before your muscles can use it. You want a sugar that requires minimal processing so the energy is available when you need it. Keep in mind that for heat-challenged athletes, sweetness and flavouring are magnified. Drinks that are too sweet or flavourful cause nausea and vomiting. Additionally, you need extra sources of calories when involved in endurance events. Sports bars, gels and meal replacements do the job.
Cramping is a prevalent problem in athletes of all kinds. The abnormal physiological processes that contribute to cramps are electrolyte imbalances (especially sodium), dehydration, lactic acidosis and hypoglycemia. When present together, these factors act synergistically to alter the way in which muscles contract and relax, leading to cramping. Optimal prevention means addressing all of these processes as thoroughly as possible. The best place to start is with a properly formulated sports drink.