The science behind muscles cramps. What they are, what causes them and how to avoid them

We’ve all been there…

Mid-exercise, or worse – in the dead of night when you’re trying to rest…

The sudden, stabbing pain of muscle cramps. Shooting up the backs of your legs. Like a machete through your muscle fibers.  

But what exactly causes muscle cramps?

In this article we’ll explain all. Taking a closer look at the science behind the searing pain.

Key points:

  • Muscle cramps are sharp, sudden muscle contractions. Exercise-associated cramps after affect the calves, quadriceps and hamstrings.
  • The underpinning pathophysiology of cramps has always been poorly understood. With many theories incorrect about why and how they occur.
  • Muscle cramps might be caused by repetitive, involuntary motor unit firing. Known as ‘cramp discharge’.
  • A prophylactic approach is recommended. With appropriate nutrition and hydration suggested to combat exercise-associated muscle cramps.
  • In the event of cramp, mild stretching can help to reduce pain through an autogenic inhibitory response.

What are muscle cramps?

 It's a good question.

A muscle cramp is a sudden, involuntary, painful contraction of a muscle or part of it, self-extinguishing within seconds to minutes and is often accompanied by a palpable knotting of the muscle

~ Minetto et al., 2013

As an athlete or serious trainer, you work hard to get your body in optimum condition. Whether it’s cardio and strength training, or power, agility and tactical work. You’re always striving to be the best you can be.

One thing is certain though…

No matter how conditioned you are (or become). You will always suffer from muscle cramps.

Unannounced. Without warning. And guaranteed to leave you bent double. Debilitated with sharp, knotted muscular pain.

Cramps aren’t the same as a spasm or generalized pain. They are their own animal. 

Acute, quick, explosive muscle pain

And through electrophysiological testing, medical professionals are able to determine the clinical root cause of cramps. Which usually include:

  • Acute pain which is localized to a single muscle (or part of a muscle).
  • Sudden, explosive pain with no “warning”.
  • Quick, spontaneous resolution. Much like how it begins. And can be eased with gentle stretching or palpitation.
  • Muscles placed in a shortened position.
  • Occurrence in modest and forceful contractions.
  • Most likely to occur in the lower body.

Electrical stimulation has demonstrated that cramps can be induced with intensities below the motor threshold.1

After testing a variety of muscles, physiologists have been able to determine a minimum frequency that passively triggers muscle cramping. This is termed the ‘muscle cramp threshold frequency’.

The problem is of course that because muscle cramps are unpredictable. So they’re difficult to measure in the real world.

Exercise-associated muscle cramps

Athletes often report muscle cramps after strenuous or prolonged exercise.

Generalized muscle cramps can affect any muscle group, but exercise-associated muscle cramps (EAMC) are more likely to occur in triceps surae (that’s calves to me and you), quadriceps or hamstrings.

From a clinical perspective, EAMC can be recognized by intense pain and stiffness2 in the muscle - which can last for a few seconds up to a few days.

Often, there’s a visible bulging or throbbing of the muscle that comes with the pain. Appearing as if the muscle is “beating”.

Cramp is most common after exercise

According to research, exercise-associated cramps can occur any time. But are more likely to occur in the 8 hours immediately after exercise.3 

Some scientists call this period the cramp prone state.

For many athletes, muscle cramps are just part of the process. But for some, it can be completely debilitating and have a significant impact on health and performance.

Cramps can affect anyone. Those with motor neuron issues, metabolic disorders or neuropathy-related conditions. Or equally in people with no history of health concerns.

Muscle cramps aren’t exclusive to athletes

Muscle cramps can occur to anybody at any time, brought on by strenuous exercise, physical labor or hot and humid conditions.

According to research,4 95% of healthy adults who have taken part in an exercise class have been affected by at least one bout of muscle cramps. Another review of the causes of muscle cramps suggested that almost 40% of all adults will suffer cramp over a typical 12-month period.

And a study5 of 2,600 endurance athletes found that as many as 67% of triathletes reported EAMC under a variety of training intensities.

What causes muscle cramps?

Most people have a theory about how muscle cramps are caused.

Ask your coach, a friend or some dude in the street and they’ll tell you that cramps are caused by alterations in blood flow… dehydration… electrolyte disturbance… or neuromuscular changes within the muscle.

(Okay, it’s unlikely a dude in the street will offer the last two explanations, but the point is – everyone has a view).

The problem is that in scientific terms, cramps are largely understudied and misunderstood. Scientists have been investigating these theories for years - because once you understand the cause, you can plan the deterrent.

The clinical presentation of EAMC is easily recognized, but its cause continues to be unresolved

~ Miller et al., 2010

The most common theory of exercise-associated muscle cramps is the dehydration-electrolyte imbalance theory.

The basis of this hypothesis is that loss of water during exercise leads to electrolyte concentration alterations which result in sensitization of nerve terminals. This in turn increases pressure within nerve endings and ultimately results in cramps.

While there’s some evidence suggesting this could be the cause of EAMC, research is limited.

At face value, this theory makes sense because hot and humid conditions can lead to increased cramping in athletes. Which some have theorized could be due to increased sweat rate.

The problem with the dehydration-electrolyte theory is that it doesn’t explain the occurrence of cramps in cooler conditions.

Fatigue, muscular overload and neural overwork

Research has shown that even in ambient conditions,6 endurance athletes still suffer from EAMC. Additionally, sweat rate and fluid loss does not appear to be correlated7 with the rate of cramping. 

The neuromuscular theory of EAMC suggests that cramps are in fact caused by neural “overwork”.

With a combination of fatigue and muscular overload creating an imbalance between the excitatory impulses (sent to the muscles) and inhibitory impulses (located in the muscles).

Modern neurophysiological research leaves little doubt that true muscle cramp is caused by explosive hyperactivity of motor nerves

~ Jansen et al., 1990

Inhibiting the sensory neurons in muscle fibers limits their ability to dampen muscle contraction. This leads to a motor unit ‘misfire’ and a discharge of muscle fibers, resulting in localized cramping.

The likelihood is that EAMC has several contributing factors. Because studies have shown that muscle cramps occur in all athletes, across all sports, in every type of environment, regardless of temperature and humidity.

The most likely cause is a combination of things - ranging from neuromuscular to physiological factors.

Treatment for muscle cramps

In the event of muscle cramps, stretching seems to be the most appropriate treatment.

Remember, EAMC is more likely to occur in a muscle that is in the shortened position. So stretching can relive cramping8 due to autogenic inhibition.

Relaxing the electrical misfiring and helping to restore the balance between excitatory and inhibitory processes within the muscle tissue.

Additional treatments may include massage, cryotherapy, active rest and electrical nerve stimulation therapy (although it should be said these are lacking in research, so considered more anecdotal).

Prevention is better than cure

Other than stretching, the only treatment with a robust base of research are beta-blockers - which is not recommended unless prescribed by a health professional.

Taking preventative measures to offset muscle cramping is the most practical approach. Plenty of nutrition and hydration prior to exercise is a good strategy, plus intra-workout supplementation when required.

Research is limited but several foods and nutrients have been proposed as effective treatment options for EAMC. Including pickle juice and mustard.

Takeaway…

Exercise-associated muscle cramp is an occupational hazard for all athletes.

And most common in athletes who train at high intensity of for long durations.

There is no definitive cause, the most robust theory seems to suggest the sudden, sharp pain comes from neural discharges in the muscle fibers. Brought about by an imbalance between excitation impulses (to) and inhibition impulses (in) muscles.   

Stretching can help to alleviate the immediate discomfort of muscle cramps, but a preventative approach is recommended.

Hydration, nutrition – supplemented if necessary – pre and during high-intensity exercise is a smart strategy for all athletes in all conditions.