Rhabdomyolysis is an issue that athletes or exercisers encounter when exposed to excessive heat and humidity, coupled with prolonged and/or intense exercise and a lack of acclimatization. During rhabdomyolysis, muscle tissue breaks down, releasing intracellular fluid into the bloodstream. Protein (myoglobin) from this fluid may then concentrate in the kidneys, causing a blockage in the renal tubules, potentially resulting in renal failure and death if not adequately treated. In addition to renal failure, other serious complications of rhabdomyolysis include metabolic acidosis, hypercalcemia (excessive blood calcium), and hyperkalemia (excessive blood potassium). Classic signs of exertional rhabdomyolysis are muscle pain and dark reddish-brown urine. Discoloration of the urine is due to myoglobin that is released into the bloodstream by damaged muscle tissue.

For persons participating in one or more intense training sessions in hot, humid environments, the two best rhabdomyolysis prevention strategies are proper hydration and acclimatization. People exercising strenuously in hot and humid environments are at an increased risk for developing rhabdomyolysis and other heat illnesses due to dehydration and hyperthermia. Athletes and exercisers should follow normal hydration protocols for training in situations where fluids and electrolytes may be lost through increased sweating. To prevent dehydration, adequate amounts of fluid should be consumed before, during, and after training in the heat. Most research supports the statement that sports drinks are superior to water in maintaining endurance performance. In addition to carbohydrates, the electrolyte content found in most sports drinks is beneficial in replacing sodium lost through sweating. That being said, don’t be afraid to make your own sports drink by substituting natural ingredients such as honey to replace artificial flavors and colors or, if your palate can tolerate it, drinking salty things such as pickle juice. In addition, dehydration can be a significant factor in tissue damage as well as tissue death, especially in untrained persons that are exercising in hot environments. Rhabdomyolysis prevention strategies should also include early fluid replacement at the first sign of dehydration.

Many factors affect a person’s ability to tolerate exercising in the heat. Such factors include environmental conditions, fitness level, hydration level, and clothing choice. In order to achieve an adequate level of heat acclimatization, it is recommended that exercise intensity and duration in the heat be gradual and on consecutive days. Adaptations to heat include decreased body core temperature, decreased heart rate, increased rate of perspiration, increased plasma volume, and an increased cardiac output — these adaptations to heat result in a decreased rate of perceived exertion and improved heat transfer.

High rates of heat exhaustion, heat cramps, heat stroke, and other heat illnesses are severe problems in football, running, and other sports that train in the heat, and steps to acclimatize at-risk athletes are necessary. For example, Division 1-A and 1-AA football teams, per NCAA regulations, are required to have a 5-day acclimatization period. This acclimatization period consists of days 1 and 2 with only the helmet for protective gear. Days 3 and 4, players are allowed to wear shoulder pads in addition to their helmets. On day 5, players are allowed to wear full protective gear. On all days, 1-5, players are only permitted to practice for (1), 3-hour period or less. On all successive days, players may practice twice daily if at least 3 hours are allowed between practice sessions. Regardless of what level of play at which the collegiate football player participates, this 5-day acclimatization period should be minimal in their acclimatization. Independently, the player should spend time outside before pre-season practices begin, performing light physical activities such as biking or jogging to better prepare for the rigors of formal training in the heat.

Athletes and exercisers that know in advance that they will be training or competing in hot, humid climates may want to travel to those types of locations prior to training and/or attempt to simulate those climates by training partially indoors, in a controlled hot environment, toward the end of their training cycle. Heat acclimatization is almost complete after 7-10 days of successive exercise in the heat, resulting in a reduced risk of heat-related illness. In addition to her heat acclimatization, athletes and exercisers will want to gradually increase their training volume and/or intensity since a lack of preparedness for intense physical stress may also lead to rhabdomyolysis.
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