Heat cramps are painful sustained contractions of skeletal muscles occurring during or immediately after strenuous physical activity, often in environments with high ambient temperatures. The exact pathophysiology of muscle cramping remains unknown. However, it is highly likely that dehydration and hyponatremia are key factors in the development of muscle cramps. Excessive sweating with subsequent hypotonic fluid replacement is known to cause hyponatremia and thus increases the risk of cramping. Magnesium, calcium, and potassium are also lost through sweating, yet their intracellular stores do not become significantly depleted and, therefore, are not a likely involved in cramping (Poynter, 2010). Sodium is a critical electrolyte in the balance of net charges across a nerve cell’s membrane and as a result plays a vital role in maintaining baseline neuro-excitability across nerve cells.
As an athlete becomes increasingly hyponatremic through ongoing sweating, the balance of net charge across a nerve cell’s membrane is affected and thus the excitability across the neuromuscular junction is altered (Poynter, 2010). This increased excitability is thought to trigger the sustained, inappropriate skeletal muscle contractions seen in cramping.
Dehydration alone may also be enough to trigger cramping through alteration in the relative concentration of interstitial sodium and neurotransmitters, resulting in hyperexcitability and cramping (Schwellnus MP, 2008).
Common risk factors for the development of heat cramps include:
– High sweat salt content (Eichner, 2008)
– Age > 40
– Sickle cell trait
– EtOH use
– Low baseline fitness
– Copious hypotonic fluid replacement
– History of previous cramping episodes
CLINICAL PRESENTATION & DIAGNOSIS
Heat cramps are a clinical diagnosis, typically manifesting as brief or sustained, painful involuntary contractions of skeletal muscle. Episodes of cramping can be as brief as a few seconds or may last an hour or more. Commonly, these contractions occur in heavily fatigued muscle groups (Schwellnus MP, 2008). The larger muscle groups of the arms and legs are at higher risk given their sustained use during exertion, with the hamstrings and calf muscles most commonly involved (Poynter, 2010).
Physical exam will reveal one or more muscle groups in tetany, associated with intense pain while the contraction is sustained. Any athlete with cramping should be assessed for more systemic signs of hyponatremia, including a neurologic exam with mental status assessment.
– Muscular strain or tear
– Tendinous strain or tear
– Nerve root irritation
– Peripheral neuropathy
The treatment for heat cramps is straightforward. Initially, the athlete should be removed from play and allowed to rest in a cool environment. The affected muscle should be held at length until the contraction resolves with a slow full stretch (Poynter, 2010). Concurrently, rehydration and salt replenishment should be occurring to prevent recurrence. Oral rehydration with an
isotonic electrolyte solution is preferable over hypotonic free water given that a large water bolus may worsen the athlete’s salt deficiency thus precipitating further cramping and other more concerning manifestations of hyponatremia. Commercially available sports drinks are effective in this regard. If unavailable, a solution of similar tonicity and salt content may be created using one-quarter tablespoon of salt in 500 cc of water. Sugar can also be added to replenish depleted energy stores (Schwellnus MP, 2008).
Once the cramping has resolved the athlete should be assessed for any injuries as well as for any systemic signs of hyponatremia. Provided that the athlete’s physical exam is unremarkable, he or she may return to play if desired. The athlete should be advised that same-day recurrence is highly likely and may precipitate other injuries. If cramping does recur, the stretching should be repeated until the cramp resolves (Poynter, 2010).
If cramping occur in more than one muscle, is prolonged, or refractory to conservative management then oral benzodiazepines such as lorazepam 1 mg PO can be used to relax the affected muscle groups. Benzodiazepines are rarely required; their use should prompt the treating clinician to more closely scrutinize the clinical situation for other possible diagnosis. If benzodiazepines are used the athlete cannot return to play and should be closely monitored (Poynter, 2010).
Dr. Erik Leci and Dr. Graham Briscoe (February 16, 2020 – ND)
Eichner ER. Heat cramps in sports. Curr Sports Med Rep. 2008 Jul-Aug;7(4):178-9. doi: 10.1249/JSR.0b013e31817ebfcd.
Poynter, D. (2010). Heat Cramps: Treatment and Prevention. Athletic Training and Sports Health Care, 205-207.
Schwellnus MP, D. N. (2008). Muscle cramping in athletes–risk factors, clinical assessment, and management. Clinical Sports Medicine, 27(1):183.