Cramps While Running: Causes, Immediate Help and Prevention

What are muscle cramps?

A muscle cramp is an involuntary, sudden and painful contraction of a muscle or muscle group that does not relax spontaneously. In runners, they most often occur in the calf, thigh (hamstrings or quadriceps) and foot.

Cramps usually occur in the second half of a longer training or competition, often in combination with fatigue. They last from a few seconds to several minutes.

The two dominant theories

Theory 1: dehydration and electrolyte losses

The classic explanation: cramps are caused by a lack of fluid and electrolytes, especially sodium, potassium and magnesium, due to sweating during exercise. This theory has been common for decades and is the basis for the marketing claim of sports drinks.

The problem: the evidence for this theory is weaker than long believed. Studies show that runners with cramps are not systematically more dehydrated or have lower electrolyte levels than runners without cramps. Dehydration and electrolyte losses may play a role, but are probably not the primary cause.

Theory 2: neuromuscular fatigue

The current dominant scientific theory, promoted by researcher Martin Schwellnus and others, states that cramps are primarily caused by neuromuscular overactivity due to muscle fatigue.

During fatigue, the sensory feedback mechanisms that normally inhibit muscles (via Golgi tendon organs) become less effective. The muscle then receives sustained stimuli without counterbalancing, resulting in an uncontrolled contraction.

That also explains why cramps almost always occur in the most tired muscles, in runners who set their pace too quickly or are undertrained for the distance they are trying to run.

What causes cramps in practice?

Both theories are not completely mutually exclusive. In practice, these are the most common risk factors:

Muscle fatigue due to too fast a pace or too long a distance for the current training level. This is the most determining factor.

Insufficient preparation: anyone who runs a race for which he or she has not trained sufficiently is more likely to develop neuromuscular fatigue.

Dehydration and electrolyte imbalance: in extreme heat, high humidity and long periods of exertion, fluid loss and sodium loss through sweat certainly play a role, even though they are not the only cause.

Tight or overworked muscles: Muscles that are chronically too tight (particularly calf and hamstring) have a smaller buffer for fatigue before cramps begin.

Insufficient carbohydrates: glycogen depletion is associated with reduced muscle functioning and increases the risk of neuromuscular disturbances.

What do you do if you get cramps while walking?

Stop or slow down immediately: Continuing while a cramp is active will make it worse and increase the risk of muscle damage.

Stretch the cramping muscle passively: in case of a calf cramp: stand, straighten the leg and pull the foot towards you (dorsiflexion). In case of a hamstring cramp: sit down and straighten the leg. The passive stretch activates the Golgi tendon organs and helps the muscle relax.

Massage gently: gentle pressure on the cramping muscle can promote relaxation.

Drink if you are dehydrated, preferably something with electrolytes.

Pickled salt or pickle water: This may sound like folk wisdom, but there is surprisingly good research showing that a small amount of concentrated salt water (such as pickle water) can stop cramps within 85 seconds, much faster than it could enter the bloodstream. The mechanism is probably neural: the salty taste signal activates inhibitory receptors in the throat and stomach that suppress neuromuscular overactivity.

Cramps after the match: the nocturnal variant

Some runners wake up at night after heavy exertion with calf cramps. This is another variant that is probably more related to dehydration, electrolyte imbalance and muscle fatigue that manifest after exercise than to neuromuscular overload during exercise.

Prevention: Drink plenty of fluids after training (including electrolytes), eat a meal with sufficient sodium and potassium (potatoes, banana, broth), and sleep with your knees slightly bent if you are prone to nighttime cramps.

Prevention

Train sufficiently for the distance

This is the most effective prevention of competition cramps. Those who are well trained will experience neuromuscular fatigue later and have a greater muscle reserve for the critical last kilometers.

Adjust your starting pace

Starting too fast is the fastest way to cramp in the second half. Anyone who overestimates his race pace will exhaust his muscles faster than necessary. Consciously running negative splits (the second half slightly faster than the first) reduces the risk of cramps.

Hydrate and eat sufficiently during long exertions

For training and competitions longer than 60 à 75 minutes: Drink regularly, absorb electrolytes and ensure sufficient carbohydrates via gels or sports drinks. Read more about nutrition while running and hydration.

Work on muscle flexibility and strength

Tight calves and hamstrings are a risk factor. Regular stretching after training and eccentric calf exercises (heel drops) improve muscle function and reduce the risk of cramps. Strength training for hip and leg muscles gives the muscles more reserve for fatigue.

Avoid switching to a higher training load without building up

Anyone who suddenly starts covering many more kilometers runs a greater risk of muscle fatigue and therefore cramps. The 10% rule also applies here.

Frequently asked questions

In summary

Cramps are mainly caused by neuromuscular fatigue, not dehydration alone. The best way to avoid cramps is to be well trained at the start, to estimate your pace carefully, to drink enough and refuel, and to support muscle function through strength training and flexibility.

→ Everything about nutrition and hydration while running: nutrition while running and hydration.
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