What causes muscle cramps?

Matt Kuzdub

March 19, 2018

Cramps have a long history in tennis...can we prevent them?

What causes muscular cramps? While it’s a story for some top players down under (check out the gut-wrenching video of Muguruza below), its occurrence isn't strictly limited to hot environments. Many players that I’ve coached over the years - have experienced cramps in normal conditions. It can happen during a practice or match, while players are stretching/recovering and can even happen much later in the day - when on the car ride home or during one’s sleep.

Common Opinions

Many believe it’s a hydration issue - just drink more water. If you know anything about water balance, you’ll know that when rapidly sweating (as occurs during intense tennis play), taking in water isn’t enough. Perhaps muscular cramps come about because of mineral and electrolyte imbalances. Have a banana, they'll say. Others argue it’s all about fitness. Brad Gilbert, during an early round Australian Open match, had this to say on the ESPN broadcast when one player began cramping deep in the 5th; “you’ve earned the right to be fitter than your opponent, it’s that simple”. Does BG have a point?

In this post, it’s my aim to answer these questions. We’ll take a look at what the science has to say, provide suggestions on how to relieve cramps and offer recommendations on how to prevent them if they do occur.

What are muscle cramps?

The technical term for muscle cramps is ‘exercise-associated muscle cramps’ or EAMC. Bob Murray, the leading expert on the topic, explains that EAMC are characterized as... “a sudden, involuntary, painful contraction of a muscle or part of it, self-extinguishing within seconds to minutes and...often accompanied by a palpable knotting of the muscle”. If you’ve ever experienced an EAMC you know that in the moment, the pain can be debilitating, and players are literally paralyzed.

EAMC don’t just occur while you’re playing. Nelson et al (2016) note that cramps can occur during exercise, immediately after exercise or can occur several hours later too. EAMC can last anywhere from 1 to 3 minutes, are characterized by pain, stiffness and bulging of the affected area and generally occur when the muscle is in a ‘shortened position’. Common affected areas include the quads, hamstrings and triceps surae (calf complex).

So what causes exercise-associated muscle cramps?

According to a recent narrative review by Nelson et al (2016), there are 2 prevailing theories on the occurrence of muscle cramps.

1. The dehydration and electrolyte imbalance theory

During intense exercise, our body cools itself through sweating. When we sweat, the cells - and in particular, those cells which are associated with muscle contractions - lose fluid. These fluids in our cells aren’t just made up of water - they hold a variety of substances including the likes of sodium, potassium, calcium, magnesium and chloride. Excessive sweating can also lead to deficits in these minerals - all of which are important for the function of various processes (including muscle contractions...which help sustain exercise intensity). This essentially leads to an unfavorable environment within the various cells of the body which results in ‘hyper-excitable’ motor nerve terminals (those that innervate muscle and produce contractions) and ‘spontaneous discharge’ (Nelson et al 2016). All of this would, in theory, contribute to some sort of twitch, stiffness or cramp-like activity within that particular muscle.

While this theory is definitely plausible, recent evidence has revealed that both crampers and non-crampers did not have differences in hydration status and serum electrolyte status during endurance events. Second, when hypo-hydrated (less than optimal hydration) vs hydrated subjects were electrically induced, there was no difference between the onset of cramping and its severity. Lastly, stretching - and activation of Golgi Tendon Organs have been reported both empirically and anecdotally, to relieve muscle cramps WITHOUT altering hydration and/or electrolyte status (Craighead et al 2017).

So, for those coaches and players that report a decrease in cramp severity (or it’s alleviation entirely) as a result of a Gatorade beverage, ask yourself, was the athlete stretching at the same time? Did enough time pass for the cramp to momentarily dissipate? Or perhaps there’s a placebo effect in place. Regardless, as we’ll see later in the recommendations section, hydration status plays a factor in muscle cramping, but it doesn’t appear to be the root cause.

2. The altered neuromuscular control theory

Before we outline the premise behind this theory, it’s important to know what muscle spindles and GTOs are. And to define these terms we must understand proprioceptors. Proprioceptors are receptors located within muscle and tendon that are capable of detecting changes in the length and force of these tissues. Proprioceptors are constantly relaying information to our conscious and subconscious ‘control centers’ - always providing info as to where we are in space.

Proprioceptors in skeletal muscle are called muscle spindles. Muscle spindles primarily detect changes in muscle length - and when a stretch is detected, they act to produce a rapid contraction (think of the stretch reflex action - i.e. knee jerk). They are excitatory in nature. GTOs are also proprioceptors but they are found within the tendinous structures of muscle-tendon units. Their primary role is to detect changes in force (in both the tendon and the muscle) for protective purposes. If GTOs sense too much tension, they’ll respond by inhibiting the activated muscle or tendon. That means that they are inhibitory in nature. One last point - these receptors have spinal reflex inputs; meaning that the message doesn’t have to be sent to the brain (as this would take too long for a response to be generated).

The “altered neuromuscular control theory,” put forward by Nelson et al (2016) posits that when an athlete gets to a point of neuromuscular fatigue, muscle spindles activity increases (i.e. produce contractions...like the bulging experienced during cramping) while GTOs have decreased activity (which doesn’t allow for alleviation of said contractions). This is why cramping usually occurs towards the end of practices and matches -and when players are more likely to hit a muscular fatigued state.

Factors that lead to fatigue and exercise-associated muscle cramps

1. Genetics

Just like some people have different tolerances to pain, when it comes to cramps, some athletes have a lower OR higher cramp threshold. Researchers call this the individual CTF (cramp threshold frequency). Research has revealed that individuals with a history of cramping also have a lower CTF. Meaning that if you cramp often, you are more susceptible to future bouts of cramping. However there is no clear indication that a lower CTF is related to family history or genetics.

2. Gender and Age

Research suggests that females are less fatigable than males. Proposed mechanisms to account for this are a greater proportion of type 2 fibers, which fatigue more readily, in males and emales using more lipids (fats) for energy during exercise. However, it’s difficult to accurately compare relative intensities of exercise. Age doesn't seem to be a factor, but not enough systematic research has been done to draw any conclusions.

3. Body Size

Logically, an increased proportion of fat mass compared to lean mass would in some way lead to fatigue (sooner), which would then contribute to cramping...but interestingly, as it currently stands, there are no correlations between EAMC and bodyweight or BMI.

4. Exercise Intensity and Injury History

There seems to be a high correlation between vigorous exercise and EAMC - not surprisingly. High level tennis requires high intensity effort sustained over long periods - which is why I believe (from experience) that most cramping episodes occur at elite levels of play. As for injury history, there is some weak evidence that suggests prior tendon and/or ligament injuries are correlated to EAMC.

Here’s what to do if a cramp presents itself...

Stretch (Lightly)

Nelson et al (2016) believe that stretching is the most effective treatment for acute cramping (i.e. relieving a cramp once it’s begun). The reason…proprioceptors in tendon (GTOs), are suppressed when muscle contracts in a shortened position, like during a cramp. When stretched, muscle-tendon fibres lengthen, providing feedback to GTOs so they can perform their role - to inhibit muscle activity, effectively ceasing the contraction and alleviating the dreaded cramp.


Two case reports found that hyperventilation (20-30 breaths/min) relieved cramps entirely - interestingly, in both cases, they DIDN’T return. In my own experiences, performing a series of deep breaths (while at the same time stretching) has had merit. Yes, these are isolated cases, but breathing techniques may be an alternative treatment strategy when other means are not available.

Drink Pickle Juice (or some other trp channel stimulator)

It is true? Studies (Miller et al 2010) have found that pickle juice drinkers had shorter cramp times in hypo-hydrated men compared to water (49 seconds shorter). Pickle juice has a high amount of salt and acetic acid. However this same study discredited the proposal that the high salt content of pickle juice restored electrolyte balances, since the study found virtually no changes in plasma electrolyte concentrations. If you don’t like pickle juice, there are now commercially available products that have been scientifically validated to work in a similar fashion.

Stay Hydrated and Electrolyt-ed

Salt tablets and magnesium supplementation are commonly used to treat and prevent cramps, but there’s currently no evidence to suggest that they work.

But just because the dehydration and electrolyte imbalance theory isn't the primary cause of muscular cramps, doesn’t mean players shouldn’t maintain adequate fluid and mineral levels before, during and after training/competition. A decrease in hydration of just 2% has been linked to severe reductions in performance and increases in fatigue. Recall that fatigue leads to EAMC...but staying hydrated for performance purposes should motivate players enough.

In order to mitigate the onset of a cramp...

Improve Physical Preparedness

It’s my belief that poor training and recovery habits are of primary concern when it comes to EAMC. I’ve seen countless examples of players who are simply ill-prepared for the demands of elite tennis play. This DOES NOT mean that they are unfit. It could mean that they are training too much. Why is it that many academy players, who train 5 hours a day, 6 days a week, experience cramping? Remember that to adapt, adequate recovery plans need to be in place - both from an active and passive perspective.

Electrical Stimulation

There’s some compelling research (Behringer et al 2016, 2017) that has found an increased CTF (cramp threshold frequency) for as long as 48 hours, when subjects were cramp-induced. Furthermore, when performed regularly (1-2 times per week), these subjects elicited nervous system adaptations that further improved the CTF (and perhaps could lead to favorable long-term adaptations).

Others (Khan and Burne 2007) found that when the Achilles tendon was stimulated, ALL subjects reported a relief from cramps in the gastrocnemius. The majority won’t have access to this type of equipment, but it does give further weight to the ‘altered neuromuscular control theory’ that cramps are nervous system related.

Massage Therapy

Some authors propose that various massage techniques can alter neural excitability, effectively reducing the potential for cramping. Like most theories on massage therapy, they lack empirical evidence and objectivity (although many colleagues of mine have reported some benefits with pre-competition massage).


I believe it’s time to rethink the way in which we prepare players for tournaments. How many matches are to be played? What are the on-court conditions like? What surface are they playing on? Time of day? Etc., etc. All of these factors must be taken into consideration weeks and months before hitting a 3-4 week competitive block.

To this end, attributing EAMC to one specific factor - poor work capacity, weak muscles, a fatigued state, stress, inadequate nutrition - is short-sighted. But from what I’ve learned over the years, it’s rarely just one thing that contributes to pain, injury or some other sport-related ailment. It’s a combination of factors. The best we can do is educate ourselves, learn from our past experiences and prepare diligently for the future.