Muscle cramp is a common symptom in healthy people. It is a sudden, painful and involuntary muscle contraction. Usually, it resolves over several seconds, minutes, or in the worst scenario after several hours.
Electrolyte Imbalance and Dehydration Hypothesis
It is commonly believed that electrolyte imbalance and dehydration issues cause muscle cramp.
Electrolytes (eg: sodium, calcium, magnesium, chloride, potassium) are involved in many essential processes in our body. They play a role in conducting nerve impulses, contracting muscles, and regulating pH levels in our body.
With the heat cramps, an athlete typically has been sweating extensively with appreciable sweat electrolytes. Extracellular fluid compartment contracts due to sweating. This can lead to mechanical deformation of nerve endings, increase in ionic and neurotransmitter concentrations, which lead to hyper excitability of motor nerve terminals and spontaneous discharge.
However, there are new researches showed that no significant differences between the concentration of blood electrolytes in marathon runners and triathlon athletes who suffering exercise associated muscle cramp and those were free from exercise associated muscle cramp. In support of this finding, the concentrations of blood electrolytes did not change even after a complete recovery after the cramp episode, which suggesting that cramp vanished was not associated with blood electrolytes normalization.
Neuromuscular Hypothesis
During a variety of intense physical activities, repeated or extended loading on muscles can lead to muscle fatigue. The muscle fatigue hypothesis suggested that such a scenario can prompt an increase in muscle spindle afferent activity and a concomitant decrease in Golgi tendon organ (GTO) inhibition leading to abnormal α motor neuron control and sustained αmotor neuron activity. Notably, shortened muscles with sustained contraction may be particularly vulnerable to such cramping.
Predisposing risk factors associated with fatigue muscle cramping might include older age, poor stretching habits, insufficient conditioning, cramping history, and excessive exercise intensity and duration, and related metabolic disturbances.
Reference:
1. Gaia Giuriatoa, Anna Pedrinollaa, Schena Federicoa, Massimo Venturelli. 2018. Muscle Cramps: A Comparison of the Two-Leading Hypothesis. Journal of Electromyography and Kinesiology 41: 89–95.
2. Michael F. Bergeron. 2008. Muscle Cramps during Exercise - Is It Fatigue or Electrolyte Deficit? Supplement 7(4): 550-555.
3. Ronald J. Maughan, Susan M. Shirrefs. 2019. Muscle Cramping During Exercise: Causes, Solutions, and Questions Remaining. Sports Medicine 49 (Suppl 2):S115–S124.