Cramping in tennis: what the evidence says and what the rulebook decided

Fifth set, or third if you are a woman, and the calf goes. What happens next is the part nobody prepares for: you cannot stop. Not properly. The rulebook has already decided that what is happening to you is not an injury, and the trainer who comes to look at you is working against a clock that does not pause.

Almost everything written about tennis cramping is written by somebody with an electrolyte product to sell. That is not a conspiracy, it is just who funds content. The result is that the most common piece of advice in the sport rests on a theory that the research has been steadily abandoning for 30 years, and the players who follow it keep cramping.

What the sport decided

Start with the rule, because it is the part that changes your afternoon.

Two different rulebooks apply here depending on where you are playing, and they are not the same. Most articles blur them, which is how a junior arrives at a professional conclusion and a professional arrives at a junior one.

On the professional tours. ATP, WTA, ITF and Grand Slam rules treat pure muscle cramping as a non-treatable loss of condition. No medical timeout is granted for cramping alone, at any point in the match. The WTA wrote this in explicitly in 2010: play cannot be stopped to treat general fatigue or muscle cramping, though cramping remains treatable when it is a symptom of another treatable condition. Heat illness is a separate matter and is treatable in its own right. What a cramping professional actually gets is the time that already exists in the match, the changeover and the set break, commonly limited to about two treatments in total.

Under USTA rules. American junior, collegiate and league tennis works differently and more generously. One 3-minute medical timeout is allowed for cramping or a heat-related condition during the warm-up and one during the match, and that limit holds even if the cramp moves to a different part of the body. Once both are used, the player is on self-treatment inside the normal windows: 90 seconds at a changeover, 2 minutes at a set break.

So the answer to whether you can stop for a cramp depends on which draw you are in. On tour, never. At a USTA event, twice, and then never.

The distinction the chair umpire has to make, in real time, is between a cramp and an acute muscle problem, and those look similar from 20 metres away. That is why the rule produces an argument every couple of seasons, usually involving someone who won.

Why the rule is more defensible than it sounds

Classifying cramp as the player's own conditioning failure sounds harsh. The research is closer to agreeing than the supplement aisle would suggest.

The idea that cramping comes from losing salt and water is old and has an honest origin: it was proposed in the 1920s to explain what happened to coal miners working long shifts in heat and humidity. It made sense there. It was then carried across to athletes for most of a century without ever being properly tested on them.

When it was tested, it did not hold up well. A study of distance runners found that serum electrolyte concentrations and hydration status were not associated with cramping. A prospective study of 210 Ironman triathletes found that what predicted cramping was increased racing speed and a previous history of cramps, not dehydration or changes in serum sodium. A separate study in ultra-marathon runners found increased running speed and pre-race muscle damage as the risk factors.

The theory that replaced it is unglamorous and fits tennis well. Schwellnus proposed in 1997 that cramping comes from altered neuromuscular control secondary to muscle fatigue: as the muscle fatigues, the excitatory signal from the muscle spindles rises and the inhibitory signal from the Golgi tendon organs falls, and the muscle is left contracting without anything telling it to stop.

Which is to say the cramp is a fatigue event, not a chemistry event. And a fifth set is a fatigue event.

The part the honest version has to include

Neuromuscular fatigue is the leading explanation, not the only one, and the tennis-specific literature is careful about this.

The 2020 review of cramping in tennis players concludes that neuromuscular fatigue plays a larger role than electrolyte deficit or dehydration, and then adds that electrolyte deficit may play more of a role in recurrent or systemic cramping specifically. It also proposes separating acute localised cramping from the recurrent kind, because they may not be the same problem.

That distinction is the useful part for a player. The person who cramps once, in the longest match of their season, in heat, is a fatigue case. The person who cramps in most hot matches, in several muscles, year after year, is a different question and worth investigating properly rather than treating with a sachet.

Tennis also has its own small literature on heat cramps going back to a case report in 1996 and follow-up work on fluid and electrolyte challenges during play in the heat. Sodium plays some part, as a secondary lever that is nowhere near as reliable as it is sold to be.

Magnesium

Nothing. There are no randomised controlled trials supporting magnesium for exercise-associated cramping, which is a stronger statement than saying the evidence is weak. The evidence is absent.

It is on the shelf because the mechanism sounds right, and a mechanism that sounds right is what most of this category sells. If magnesium made a difference to cramping in athletes, it is the sort of thing that would have been demonstrated by now. The same reasoning is why the potassium explanation for the banana does not hold either.

What actually lowers the risk

Train at the intensity you intend to compete at. Every prospective study that found a real predictor found the same one: going harder or longer than you are prepared for. A player whose training weeks never include a 2-hour high-intensity session is not prepared for a 3-hour match, and no drink fixes that on the day.

Know your own history. Previous cramping is one of the most consistent risk factors in the literature, and a family history shows up too. If you are the player who cramps, you are running a different risk profile from your opponent and should plan accordingly, which means pacing and preparation rather than a bigger bottle.

Acclimatise to heat if you are travelling into it. Heat raises the fatigue cost of the same work, and fatigue is the mechanism. The protocol, and what to do with the 10-minute break the rules now give you, is set out in the piece on heat.

Drink and salt sensibly, because being dehydrated is bad for other reasons and hyponatraemia from drinking plain water in volume is genuinely dangerous. Just do not expect it to be your cramp insurance.

When it happens anyway

Stretch the muscle. Passive stretching of the affected muscle remains the standard immediate treatment, and it is consistent with the neuromuscular explanation: you are restoring the inhibitory signal that fatigue removed.

Pickle juice and similar rapid-relief agents have some support for shortening cramp duration in laboratory settings, and the proposed mechanism is a reflex from the mouth and throat rather than anything reaching the muscle in time. Reported outcomes are mixed. Know about it, and do not build a plan around it.

And know the clock you are on, because that is the tennis-specific part. Your treatment window is the changeover. Nobody is going to pause the match while you recover, and the sooner you accept that the sooner you can decide whether you are finishing.

What I would tell a player

If you cramp once in the longest, hottest match you have played, you were not deficient in anything. You were doing more than your training had prepared you for, in conditions that raised the price, and your nervous system stopped inhibiting a muscle that had been asked to work for 3 hours.

If you cramp often, stop buying products and go and get it looked at properly, because recurrent cramping is a different category and may have a cause worth finding.

And either way, read the medical rules for whichever draw you are actually in, because they differ, and read them before you need them. Every player learns them eventually. Most learn them while sitting on a chair with a locked calf, being told that what is happening to them does not count.

Common questions

Educational material, not medical advice. Recurrent or severe cramping should be assessed by a qualified health professional.