Muscle Cramps: Causes and Solutions.

The Most Mysterious Phenomenon in Sports Science?

Nov 30, 2024

That intense and seemingly endless bolt of pain that shatters your hopes in a race and the fruits of many days of training—that’s a muscle cramp.

Cramps are arguably the least understood phenomenon in sports today. Although numerous theories have been proposed to explain their occurrence, none sufficiently clarify why they happen, as no single theory alone correlates well with the onset of cramps.

In the scientific realm, cramps are defined as spasmodic, involuntary, and extremely painful muscle contractions that occur during or after intense sports practice.

Nearly every athlete has suffered cramps at some point, yet the origin of cramps and how to prevent them remain a mystery.

In this article, I will shed light on the latest theories regarding cramp onset and the factors that may make you more prone to suffering from them or help you avoid them. I’ll even include tips to rescue yourself when it seems too late and you’re already in the "clutches" of a cramp.

Why Do Cramps Occur? Various Theories

1. Cramps Due to Electrolyte Imbalance or Dehydration

The first observational studies on cramps were conducted 100 years ago among miners working in highly humid and hot conditions.

The miners experienced cramps, and they were dehydrated. Scientists soon connected the two, leading to the theory that dehydration and electrolyte deficiency—such as sodium, magnesium, potassium, etc.—were behind the occurrence of cramps.

However, a primary issue with this association is that sweat is always hypotonic, even in individuals who sweat more "salty." This means the sodium concentration in sweat is always lower than in blood. Therefore, the more we sweat, the higher the sodium concentration becomes in the blood.

Put differently, sweat is more diluted than blood, containing fewer mineral salts. While electrolytes are indeed lost through sweating, they are lost in a smaller proportion compared to water. Hence, electrolyte deficiency alone wouldn’t trigger cramps.

Moreover, if dehydration affects the whole body, why do cramps only occur in the muscles that are most actively used?

Scientific Studies

In 2004, a significant study on ultradistance runners (56 km) attempted to test this theory. Scientists analyzed plasma electrolyte concentrations before and after the competition and their association with cramp occurrence.

The main conclusion was that there was no statistically significant association between sodium, magnesium, potassium levels, and cramp onset. An unexpected finding from this study was that those who suffered cramps showed less dehydration (weight loss) than runners who didn’t experience cramps. Thus, it suggests no connection between dehydration or electrolyte levels and cramp occurrence. This study offered additional interesting insights that we will explore further.

The most significant finding was that there was nothing significant...

The following year, the same group of researchers conducted a more advanced study with Ironman competitors. Again, the conclusion was similar, and once more, the group of athletes who experienced cramps ended up slightly more hydrated than those who didn’t.

But without a doubt, the "final blow" to this theory came from a 2010 study at the University of North Dakota, funded by Gatorade in the hope of establishing a clear link between electrolyte depletion—which they produce—and cramps. Unexpectedly, the researchers concluded that a 3% dehydration level doesn’t appear to indicate a predisposition to cramping. Furthermore, they acknowledged that cramps seem more related to neuromuscular fatigue than to hydration status.

3. Cramps Due to Neuromuscular Fatigue

Since the dehydration theory seemed unlikely, an observational study from the University of Cape Town—a questionnaire for athletes who had experienced cramps—suggested that cramps might be caused by muscle fatigue. One of the leading researchers, Schwellnuss, theorized that cramps are triggered by an abnormal, sustained activation of muscle innervation, seemingly due to a neural malfunction.

To explain this, let me simplify the highly complex process of neural stimulation in muscle contraction.

Striated muscle is tissue we can voluntarily control. When the brain signals to contract a muscle—for example, the quadriceps during a pedal stroke—it sends a nerve impulse down the spinal cord. From there, specific nerves called motor neurons carry this electrical signal to the targeted muscle.

This electrical impulse makes the muscle fibers it reaches contract for as long as the impulse lasts, producing movement.

Muscles continuously alternate between contraction and relaxation phases. In proper pedaling form, the muscle contracts during the push phase and relaxes during the recovery phase. In another movement, like a jump, the quadriceps muscle contracts briefly during takeoff and relaxes once the propulsion phase is complete.

A cramp occurs when the muscle can’t relax after a contraction. The muscle remains contracted because the electrical impulse continues to arrive due to a failure in the motor neuron.

The real question, then, is: why do these motor neuron failures happen? Why do cramps occur?

Although many factors have been linked to cramp onset, one factor encompasses them all and is consistently present in the scientific literature: fatigue.

Fatigue as a Cause of Cramps

One of the main clues suggesting that fatigue causes cramps is that they only appear in active muscles—particularly in muscles that cross two joints and work in a shortened position.

For example, calf muscle cramps are common among swimmers: these muscles remain in a shortened position due to the ankle extension required for swimming.

Cramps typically occur during competitions, especially in the latter stages when athletes are more fatigued.

Reviewing Schwellnuss's work, which is invaluable, several intriguing conclusions emerge beyond his initial hypothesis:

Starting Too Fast: Athletes who suffered cramps began their races at a pace, on average, 13 minutes faster than those who didn’t cramp.
Muscle Fatigue: In the three days leading up to the race, cramping athletes had trained almost twice as much as those who didn’t cramp.
Muscle Damage: Athletes who cramped showed higher levels of creatine kinase (CK) before the race, a marker of muscle damage. They also reported greater calf pain.
Stretching Before the Race: 93% of athletes who cramped had stretched before exercise, while only 54% of athletes who didn’t cramp had stretched.

Within this theory, the exact physiological basis of cramps remains unclear. Scientists are divided into two main camps:

Central Origin: In simplest terms, they argue that fatigue originates at the central nervous system level, causing hyperexcitability of motor neurons.
Peripheral Origin: They believe muscle fatigue disrupts motor neuron function.

Currently, the peripheral origin theory has more evidence, though it’s easier to measure than central fatigue. Likely, both theories coexist, as they aren’t mutually exclusive. For further reading, see Buskard's paper on this topic.

In practice, it doesn’t matter which side is right since both likely are, and they agree on one point: fatigue causes cramps.

Now, does mental fatigue affect cramps in the same way as muscle fatigue?

Factors That Increase Cramp Likelihood

As discussed earlier, any cause that intensifies mental or muscular fatigue will increase the likelihood of cramping.

From scientific literature and practice, several factors are linked to a higher incidence of cramps:

Muscle Damage: Elements like pace, tapering, heat, and dehydration.

Without a doubt, muscle damage is the primary factor associated with cramp onset. There has been a tendency to oversimplify this by linking cramps to poor training condition, but observational evidence is clear: even elite athletes in peak physical form experience cramps. A quick search reveals examples of top cyclists in their best form during the season who still suffer from cramps.

In general, any stressor (physical or environmental) that increases fatigue will also increase the predisposition to suffer from cramps.

As you may have personally experienced, cramps tend to appear at the end of a very demanding event, when fatigue is at its peak.

Generally, when we suffer from cramps, the initial pace has been too fast for what we could sustain. We have created damage that we are no longer able to repair.

Muscle damage prior to the event has also been linked to an increase in cramps, as has insufficient training. Typically, cramps occur at the beginning of the season (due to lack of adequate training) or at the end of it (due to fatigue).

Dehydration or heat alone do not cause cramps, but they do facilitate them by increasing the fatigue experienced by the athlete.

Genetics

There is no doubt that some people are genetically more prone to cramps—as is my case—than others.

In some experimental studies (study), it has been shown that under the same electrical load (which simulates the potential of a nerve), some people experienced cramps while others did not. People who require a lower electrical potential to produce contraction are systematically associated with more cramp episodes.

This may be the most important factor after muscle damage, and even if everything else is done well, if you are prone to cramps, you will likely have to deal with them again.

Stress and Mental Fatigue

As we have seen, any stressor that influences the central nervous system has the potential to increase our chances of experiencing cramps.

Chronic or acute stress and mental fatigue can cause temporary damage to the structures and function of the nervous system (article), which can lead to an overexcitation of motor neurons and make them more susceptible to causing cramps.

Training sessions that are very similar to competitions don’t tend to cause the cramps that competitions do in many athletes, who even begin to experience cramps in muscles that were barely used during the event (arms, fingers, etc.). In fact, cramps often appear more frequently on descents, when changing position, or when about to fall.

Given their multifactorial and complex nature, it’s impossible to attribute cramps to a single cause. However, I have observed a strong correlation between the occurrence of cramps in competition and the athlete’s nervousness or lack of experience. It seems that heightened activation during competition—exacerbated by stress, anxiety, caffeine, etc.—can alter the contraction-relaxation cycle of the muscles, reducing the relaxation time in each pedal stroke and, consequently, increasing the likelihood of cramping.

This aligns with common observations: less experienced individuals tend to experience cramps more frequently, which gradually diminishes with experience. Additionally, caffeine significantly increases the likelihood of cramps, as it activates the sympathetic nervous system, putting us on high alert.

Personally, in my athletes, I have observed and related that cramps tend to be more frequent in weeks when they report higher work or personal stress. Additionally, episodes of intense acute stress, such as falls (or nearly falling), are very strongly associated with the appearance of subsequent cramps.

Caffeine Consumption
Although there are no scientific studies linking caffeine to the occurrence of cramps, theoretically, caffeine consumption can increase cramps by acting on both ends: the nervous system and muscles.

Caffeine could increase the hyperexcitability of motor neurons and nerves throughout the nervous system.
Caffeine allows you to perform at a higher level and therefore accumulate more muscle fatigue. This greater fatigue will give you more chances of suffering from cramps.

Now, should you stop consuming caffeine out of fear of cramps? My opinion is that you should not. Generating higher performance should be our priority, even if it increases our risk of cramps.

Stretching
Continuous stretching sessions have been associated with more cramp episodes (study). But interestingly, in the face of a cramp, stretching is the best way to relieve it and prevent it from recurring soon after (study).

Age and Gender
Some studies, like this one and this one, find that athletes over 50 years old are more prone to cramps than younger athletes.

Furthermore, they found that proportionally men are more susceptible to cramps than women.

How Can We Reduce the Likelihood of Cramps?

If cramps are caused by fatigue, the straightforward answer is simple: any technique that reduces fatigue (physical or mental) will decrease the likelihood of cramps.

Among the most effective methods, we have:

Carbohydrate and Electrolyte Intake During Exercise.
Proper Tapering: Arriving at the race without prior muscle fatigue.
Good Prior Training: Being prepared for the demands of the competition.
Reducing Stress in the days leading up to the event and increasing sleep hours.
Improving Maximum Strength, which will reduce muscle damage caused by a given effort.
Enhancing Aerobic Capacity, which will reduce fatigue resulting from exercise.

Now, there are other lesser-known strategies that I'll share with you. There are many more, but I'll only mention those that have a scientific foundation and make logical sense based on evidence:

Correct Biomechanics
Improper positioning during pedaling or running can cause muscles to operate outside their ideal range, working in shortened or overstretched positions, which can greatly increase the risk of cramps and injury. Remember that a chain’s strength is equal to its weakest link. If you don’t pedal correctly, you’ll end up with injuries and cramps that will hinder your progress.

Hyperventilation
A 2011 study showed that hyperventilation strategies could prevent cramps or reduce them once they occur.

TRP (Transient Receptor Potential Ion Channels)

Accidental discoveries, such as the finding that mustard, chili peppers, and pickle juice reduce cramp incidence (study), have led scientists to believe that factors beyond fatigue contribute to cramp onset.

These spicy foods contain molecules that activate ion channel receptors, stimulating nerves in the digestive system, which is why we perceive them as "spicy." They don't actually burn us but trigger the same nervous response as if there were fire in our digestive tract.

Nobel laureate neuroscientist Rod MacKinnon is behind a company that commercialized a product based on these receptors to prevent cramps. This product, called Hot Shot, has generated over $100 million since its launch, though I can’t confirm its effectiveness. Given its high price, one might wonder if spicy foods like chili, ginger, mustard, or pickles could have a similar effect.

An Old Trick

Imagine this: You’re competing in a crucial race, in the lead group, approaching the final climb. You attack and… cramps!

Is everything lost?

Professionals have a "trick" for such situations. It may not always work, and the cramp could return, but it will often lessen the cramp’s intensity temporarily, allowing you to continue without stopping.

The technique involves triggering an automatic defense reflex by pricking the cramped muscle. This prick activates the flexion reflex, where pain receptor stimulation generates an automatic response in the flexor muscles of the joint.

For example, the quadriceps extend the knee. By pricking it, the reflex causes contraction of the antagonist muscles (e.g., the hamstrings), relaxing the agonist muscles and thereby ending the cramp.

While this may sound unconventional, it has been used successfully in the professional field for many years, despite the lack of published studies. Another example of experience often leading science.

How to Do It?

People typically use one of the pins from their race bib. Personally, I like to be more prepared: if I expect a tough race, I carry a clean pin, sanitized with alcohol, in the fold of my jersey for easy access. Being prepared is always wise!

Pricking your own quadriceps might sound daunting, but when a cramp hits, that pain will likely be the least of your worries.

If done quickly and shallowly, the cramp should disappear—temporarily—and there shouldn’t be any blood.

Note, the goal is to trigger the reflex, not harm the muscle. Make sure the prick is very superficial.

CONCLUSION

Cramps remain a mystery and a nightmare for most athletes.

While we know of various factors that increase or decrease the likelihood of cramps, science has yet to uncover the exact physiological mechanisms behind this failure in motor neurons.

We understand that cramps aren’t caused by electrolyte deficiency or dehydration, as was once believed, but rather by an increase in muscle fatigue. Any stressor—physical, environmental, or mental—that increases fatigue also raises the probability of cramps.

Some mechanisms and techniques have been proposed to reduce or prevent cramps, such as triggering the flexion reflex or activating TRP receptors.