Athletes get muscle cramps primarily because intense exercise disrupts the normal signaling between nerves and muscles, causing involuntary, painful contractions. The problem is remarkably common: up to 67% of triathletes and 30% to 50% of marathon runners experience exercise-associated muscle cramps. While dehydration and lost electrolytes play a role in some cases, the leading explanation points to fatigue-driven misfiring in the nervous system.
The Nervous System Loses Its Balance
Your muscles don’t just contract and relax on their own. Two key sensors work together to keep contractions smooth and controlled. Muscle spindles send “contract” signals to the spinal cord, while Golgi tendon organs (sensors embedded in your tendons) send “ease up” signals. During normal activity, these two systems balance each other out.
When a muscle becomes fatigued, that balance breaks down. Research in animal models has shown that after fatiguing stimulation, about half of the excitatory spindle fibers increased their resting activity, essentially telling the muscle to keep contracting. At the same time, the inhibitory tendon organ signals became weaker and slower. The result is a nervous system stuck in “go” mode with a broken brake pedal. Motor neurons fire excessively, and the muscle locks into an involuntary contraction.
This explains a pattern athletes often notice: cramps tend to strike muscles that are already working in a shortened position. A calf cramp while pointing your toes, for example. When a muscle is shortened, there’s less tension on the tendon, which means less inhibitory feedback from the tendon organs. Combine that reduced braking signal with the heightened excitatory firing from fatigue, and you have the recipe for a cramp.
Sodium Loss and Dehydration
The neuromuscular fatigue theory doesn’t explain every cramp. Some athletes, particularly those who sweat heavily in the heat, experience whole-body cramping that affects multiple muscle groups at once. This pattern is more consistent with significant sodium loss through sweat.
A study of football players training in hot conditions (wet bulb globe temperatures of 29 to 32°C) found a telling difference between cramp-prone and non-cramping players. After about two hours of practice, players without a cramping history maintained stable blood sodium levels. Cramp-prone players, however, saw their blood sodium drop, and three of six cramp-prone athletes fell below 135 mmol/L, a threshold associated with low sodium. Their average in that subgroup was just 131.7 mmol/L. Sweat sodium concentrations also tended to be higher in the cramp-prone group (about 53 mmol/L compared to 38 mmol/L), meaning they were losing more sodium per liter of sweat.
Even mild dehydration, a loss of just 1% of body weight, measurably increases blood concentration. The American College of Sports Medicine recommends preventing fluid losses greater than 2% of body weight during exercise and notes that individual sweat rates vary widely. A simple way to estimate your personal sweat rate is to weigh yourself before and after exercise.
Heat Makes Everything Worse
Hot, humid environments accelerate both of the mechanisms above. You fatigue faster in the heat, which pushes the nervous system toward that imbalanced state sooner. You also sweat more, losing fluid and sodium at higher rates. Endurance athletes competing in hot conditions face the highest risk because they’re combining prolonged effort with significant fluid and electrolyte losses over hours of activity.
Acclimatization helps. Athletes who gradually adapt to hot conditions over one to two weeks typically see their sweat become more dilute (lower sodium concentration per liter) and their bodies become more efficient at cooling. This is one reason cramps are more common early in a hot-weather season or when athletes travel to warmer climates for competition.
Some Athletes Are Genetically Predisposed
Not every athlete who trains hard in the heat gets cramps, which has led researchers to look at genetic factors. A study examining genes involved in connective tissue found that variations in the COL5A1 gene, which codes for a component of collagen in tendons and ligaments, were associated with cramping history. Specifically, one version of the gene (the CC genotype) was significantly more common in athletes who had never experienced exercise-associated cramps (21.8%) compared to those who had (11.1%). This was the first identification of a specific genetic marker linked to cramping susceptibility.
The connection likely relates to tendon compliance. If your connective tissue transmits force differently, it could alter how effectively your Golgi tendon organs sense tension and send those crucial inhibitory signals. This is still an emerging area, but it helps explain why two teammates doing the same workout in the same conditions can have completely different cramping experiences.
Why Stretching Works Immediately
The most effective immediate treatment for a cramp is stretching the affected muscle, and the neuromuscular theory explains exactly why. Stretching increases tension on the tendon, which activates the Golgi tendon organs. This sends a burst of inhibitory signaling to the overexcited motor neurons, essentially reapplying the brakes. The nervous system resets, and the involuntary contraction releases.
Pickle juice has gained attention as another quick remedy. The proposed mechanism involves acetic acid (the main component of vinegar) stimulating specific receptors called TRP channels in the mouth and throat. Activating these receptors is thought to trigger a reflex from the brain that dials down the hyperexcitable motor neurons. One study found that pickle juice reduced cramp duration to roughly 69% to 83% of the time it took cramps to resolve with water alone, though the researchers noted the effect was not as robust as earlier studies had suggested. The speed of relief (often within seconds of swallowing) makes it unlikely that the mechanism is about replenishing electrolytes, since the small volume of liquid wouldn’t reach the bloodstream that quickly.
What Actually Helps Prevent Cramps
Since fatigue is the dominant trigger, anything that delays fatigue reduces cramping risk. Proper conditioning for your sport is the single most important factor. Athletes who ramp up training volume or intensity too quickly are more likely to cramp because their muscles fatigue earlier relative to the demands of the activity.
Hydration and electrolyte replacement matter, particularly for heavy sweaters and those exercising in heat for more than an hour. Drinks containing sodium and carbohydrates offer benefits over plain water during prolonged exercise. Because sweat rates and sodium losses vary so much between individuals, a personalized approach works better than following generic guidelines. Tracking your body weight before and after training sessions gives you a practical measure of how much fluid you need to replace.
Magnesium supplements are widely marketed for cramp prevention, but the evidence is underwhelming. A Cochrane review found moderate-to-high quality evidence for magnesium’s effects on nighttime cramps in older adults, but no strong evidence specific to exercise-associated cramps. If you’re not deficient in magnesium, supplementation is unlikely to make a difference for workout-related cramping.
Adequate fueling also plays a role. Muscles that run low on glycogen fatigue faster, which circles back to the core neuromuscular problem. Eating enough carbohydrates to match your training demands, particularly before and during long endurance efforts, helps keep the fatigue-driven signaling imbalance at bay longer.