Understanding possible causes and prevention methods for cramps induced by exercise
Cause of cramps still not clearly established
Exercise-associated muscle cramps (EAMC) are a common condition defined as skeletal muscle cramps that occur during or shortly after exercise. Typical signs of EAMC include acute pain, stiffness, visible knotting of the muscle, and possible soreness lasting for several days. Though the clinical presentation of EAMC is easily recognized, the exact cause of cramps remains unresolved and controversial. In approaching EAMC, those studying it feel a better understanding of the underlying mechanisms that cause it can allow for better prevention and treatment. Traditional belief attributes exercise in hot and humid conditions to be responsible, while newer evidence suggests a neuromuscular cause. This disparity has created a number of different prevention/treatment approaches, and the need for a more cohesive strategy is clear. Noting this, a comprehensive guide was created that analyzed theories on EAMC causes and sought to deliver better prevention and treatment tips.
Two opposing theories
The two main schools of thought on EAMC are the dehydration-electrolyte imbalance theory and neuromuscular theory. The former, and most common among health professionals, says that because the body doesn't store enough water for exercise and certain athletes don't ingest enough water to replace the amounts they lose during exercise, EAMC are the result of fluid and electrolyte depletion. Furthermore, exercise in hot and humid conditions exacerbates the amount of fluid and electrolytes lost, which facilitates cramps. There is strong research to support this theory, however, it fails to address why athletes competing in cool environments still experience cramps. Therefore, while EAMC may be more likely to occur in hot and humid environments, they're not necessary. Treatment using this concept also shows the theory somewhat flawed: if EAMC were due entirely to dehydration, then fluid replacement would cure them, yet a study showed that even when carbohydrate-electrolyte fluids were ingested at a rate that matched sweat loss, EAMC still occurred in 69% of athletes.
The neuromuscular theory claims that muscle overload and neuromuscular fatigue cause an imbalance between excitatory (accelerating) impulses from muscle spindles (a sensory end organ) and inhibitory (restraining) impulses from Golgi tendon organs (GTOs- sensory nerve endings). These localized EAMC tend to occur when the muscle is contracting, where the reduced tension in the muscle tendon predisposes the muscle to cramp from the imbalance between excitatory and inhibitory drives to the alpha motor neuron (responsible for muscle contraction). The enhanced excitability at the spinal level results in an increase in alpha motor neuron discharge to muscle fibers and produces a localized muscle cramp. Research supporting this theory is stronger than that for dehydration, but still has flaws. The main problem is that neuromuscular fatigue was found to occur in animals with stimulation at high frequencies (>100 Hz), but normal human muscle frequencies are usually lower than 30 Hz, which means it's unclear if human muscles become stimulated enough in physical activity to reach levels of fatigue that would bring about EAMC. Based off these and other inherent issues with each theory, it seems fair to conclude that because EAMC occur in a variety of situations, environmental conditions and populations, it is unlikely that a single factor is responsible for causing them directly. It's more likely that EAMC are due to a combination of factors that simultaneously occur under specific circumstances in each athlete.
Treatment and prevention for EAMC
Pushing anecdotal and unsupported treatments to the side and assuming that a relationship between dehydration-electrolyte imbalance and EAMC exists, professionals recommend that athletes prone to muscle cramping add 0.3-0.7 g/L of salt to their drinks to avoid muscle cramps. Stretching, quinine and beta-blockers have stronger levels of evidence to support their use; however, the most common treatment prescribed is stretching, which has proven to be effective for EAMC and other types of cramps. In regards to a preventative strategy, despite the lack of direct evidence, maintaining hydration and adequate electrolyte levels is strongly suggested. Monitoring an athlete's body weight is an easy method of ensuring adequate fluid replacement and individualizes each athlete's fluid needs. It can be said that an athlete who ingests a liter of water or hypotonic sports drink at least one hour before competition can be confident the majority of the fluid, electrolytes and nutrients have been absorbed and are available in the body.
-Summarized by Greg Gargiulo
-As reported in the July/August '10 edition of Sports Health
