There was a study published in June 2022, that aimed to compare dehydration variables, electrolyte levels, and muscle damage markers between runners who suffered from exercise-associated muscle cramps and runners who did not experience exercise-associated muscle cramps over the course of a road marathon.
Before and after the marathon, blood and urine samples were taken and body mass was measured. There was no difference between crampers and non-crampers in their sodium and potassium concentrations or body mass.
Conversely, crampers exhibited significantly greater post-race creatine kinase* and lactate dehydrogenase**. Accordingly, runners who suffered from exercise-associated muscle cramps did not exhibit a greater degree of dehydration and electrolyte depletion after the marathon but displayed significantly higher concentrations of muscle damage biomarkers.
Separately, Dr. Tim Noakes (who was a reputable source at the time of his research) found that:
There is not a single study that shows abnormal blood electrolyte concentrations at times of exercise-associated muscle cramps.
There is not a single study that demonstrates dehydration to be a factor in cramping.
There is no evidence that core body temperature plays a role in cramping.
Despite the high prevalence of cramping, its cause, treatment and prevention are not well understood. However, it does not appear to be the result of dehydration or electrolyte depletion. Athletes who suffer with exercise-associated muscle cramps should look for other causes such as inadequate training or poor pacing.
Another study published in 2015 focused on subjects running the 2014 Western States Endurance Run, a notoriously hot 100 mile race run in California in late June. The study found that muscle cramping was more common in those individuals with a history of cramping and greater muscle damage during an ultramarathon, suggesting an association with relative muscular demand. Impaired fluid and sodium balance did not appear to be the cause of muscle cramping during an ultramarathon. So what else might be happening? The alternative hypothesis used to explain exercise-associated muscle cramp boils down to neuromuscular fatigue and muscular fatigue. This hypothesis suggests that muscle overload and fatigue affects the balance between excitatory drive from muscle spindles and the inhibitory drive from the Golgi tendon organs (GTO). Essentially there is a breakdown between the cycle of contract and relax, where the muscle continues to contract at the same time the GTO sees a reduction in its inhibitory response. In this hypothesis we may see cramp as a result of poor pacing and/or lack of conditioning for the specifics of the event. It's important to note that different mechanisms may apply in different situations. The best way to manage the prevention of exercise-associated muscle cramp is to: 1. Prepare for the demands of the event 2. Have a sound pacing plan 3. Fuel and hydrate relative to your needs
References:
*Creatine Kinease (CK) is an enzyme found mostly in skeletal muscle and the heart as well as the brain. Increased levels of CK in the blood indicate an unusual level of muscle breakdown.
**Lactate dehydrogenase is an enzyme that forms part of the anaerobic metabolic system. Its role is to assist in converting lactate to pyruvate which allows it to become a fuel source.
Noakes, T 2012, Waterlogged: The Serious Problem of Overhydration in Endurance Sports, Human Kinetics Hoffman MD, Stuempfle KJ. Muscle Cramping During a 161-km Ultramarathon: Comparison of Characteristics of Those With and Without Cramping. Sports Med Open. 2015;1(1):24. doi: 10.1186/s40798-015-0019-7. Epub 2015 May 21. PMID: 26284165; PMCID: PMC4532703.
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