Exercise-Associated Heat Cramps

Sarah Schultz

Tis the season for all sorts of athletes to get cramps when exercising. Whether you play football, tennis, run or bike, exercise-associated heat cramps (EAHC) can be quite painful and debilitating. As an athletic trainer, I am often called out on the field during a football game to stretch out a calf. Athletes are usually told to drink more and eat a banana…is there any truth to this? And what causes these cramps anyways?

EAHC are complex. These cramps are painful, involuntary contractions of a muscle during or shortly thereafter exercise, lasting up to eight hours after activity. While there are many theories why cramps happen, there is not strong evidence to promote either.

The first theory is dehydration and electrolyte loss, usually caused by exercising in heat and humidity. Believers in this theory state the body does not store enough water for exercise, nor do athletes ingest enough water to replace sweat lost during exercise. Thus, a significant loss in water with no electrolyte replacement would lead to dehydration. However, this theory does not explain EAHC that occur in cool weather.

Further research found that sweat rate and sodium/fluid losses are not different in crampers versus non-crampers. If EAHC were due to fluid loss then the simple solution would be to drink more. However, when sports drink was ingested at a rate that matched sweat loss, EAHC still occurred in 69 percent of the subjects. It is interesting to note that stretching almost immediately relieves the cramp and that does not involve fluid replacement. Frequently the athletes who experience EAHC are dehydrated so restoring fluid levels to combat heat illness is warranted.

The second theory of EAHC is that muscle overload and neuromuscular fatigue cause an imbalance between excitatory and inhibitory impulses within the muscle. This is a lot of medical mumble jumble that is best explained by saying there is increased excitability at the spinal cord, which signals to the muscle fibers, resulting in a local cramp. Most muscle cramps appear in two-joint muscles, such as the quadriceps, hamstrings, and calf; all of which are used when running. There are a few limitations to this theory as well; one, it is difficult to replicate EAHC in a laboratory and two, it is not known how fatigued the muscle needs to be to reproduce a cramp and this may vary with each athlete.

EAHC are most likely due to a combination of factors that are still unknown. How do we treat them? Stretching and massage are the most beneficial treatment options. We know that immediate stretching relieves the cramp as long as the stretch is applied. How can we prevent cramps? Studies suggest ingesting one liter of water or sports drink at least one hour prior to competition and maintaining a hydration level of 1.8 liters per hour of exercise. Pickle juice, salt tablets and magnesium have little scientific evidence to support supplementation. Plyometric exercises, proper conditioning and extra carbohydrates are also suggestions for preventing EAHC.

Sports Health: Exercise-Associated Muscle Cramps: Causes, Treatment and Prevention by Miller et al (2010)

Medicine Today: Exercise-Associated Muscle Cramps by Sophie Armstrong and Tom Cross (2013)

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