Cramping in Soccer: What the Research Shows, and What It Doesn’t

You go down late in the second half, hand on the back of the calf. Somebody says “electrolytes.” Somebody else points at the salt dried on their jersey. By the car ride home you’ve been told to buy a different sports drink and simply drink more water.

Most of that advice traces back to one idea: that athletes who cramp lose more salt in their sweat than athletes who don’t. Simple, intuitive, and researchers have now tested it several times. It hasn’t completely held up the way the sideline version does, and what has held up is more useful anyway.

The short version: in the studies that have compared them, athletes with a history of cramping have not consistently shown saltier sweat than athletes without one, with American football the single exception. What has separated them is a prior calf cramp and going harder than the rest of that week’s training supported. Sodium still matters, in what gets replaced after heavy losses as diluted sodium concentration in the body could still be a factor.

Where the salty sweater idea comes from

The study people are usually reaching for looked at ten Division I American football players during a two-a-day camp. Five had a history of what the researchers called heat cramps. Five, matched for weight, age, race and position, had never cramped. The cramp-prone group’s sweat carried about twice the sodium, for those who like numbers.

A real result worth taking seriously. It’s also five against five, in college players who were adults, in American football, and the two groups sweated a similar amount overall. The difference was in concentration, not in how much they sweated.

So the idea has a foundation. The question is what happened when it got tested again, with more players and tighter controls.

What happened when researchers compared crampers to non-crampers

The largest test came in 2020. Researchers measured sweat rate and sweat sodium concentration in 350 collegiate athletes across 11 sports, with slightly different numbers contributing to each measure, comparing those who reported a history of cramping against those who didn’t. Neither sweat rate nor sweat sodium separated the two groups. One exception, and it’s the same sport as the original study: in American football, sweat electrolyte content and sweat rate did discriminate cramp-prone athletes. In every other sport in that dataset, they didn’t.

A 2022 laboratory study tightened the controls. Not an independent team, since one author overlaps with the 2020 study, but it controlled what a field study can’t. Thirty people, only eight of whom had no cramping history, ran in the heat with diet, starting hydration, fluid intake and environment all controlled. No difference in sweat sodium, potassium or chloride.

And a 2009 study of adult American football players, six cramp-prone against eight in a reference group, found sweat sodium of 52.6versus 38.3 millimoles per liter with no statistically significant difference. Even in American football, where sweat has been examined most, the finding does not replicate cleanly. In soccer specifically it has been examined much less.

Worth saying plainly: those studies compared athletes who reported a history of cramping against athletes who didn’t. Nobody was watching people cramp. That’s narrower than “salt has nothing to do with it,” and it’s what the evidence supports.

Where sodium does show up

That same 2009 football study measured more than sweat. Across a session in the heat, the reference group’s blood sodium concentration stayed flat while the cramp-prone group’s tended to decline, three of the six finishing below 135 millimoles per liter, and those players drank a significantly greater proportion of their fluid as plain water.

The signal is in what an athlete replaces heavy losses with. How salty their sweat was to begin with is a separate question, and the one without as much direct evidence behind it.

What did predict cramping

Two things have come out of prospective studies, where researchers decided what to measure and then followed athletes forward to see what happened.

The first is having cramped before. A study followed 103 male rugby league players across a full season, testing fourteen variables including age, position, cramping history, foot posture, calf girth and hydration status measured on game days. A history of calf cramping came out ahead of all of them, raising the odds roughly elevenfold. Half the squad, 52 of 103, cramped in the calf at least once.

That range is wide so keep in mind that it’s not 100% guaranteed. Read it as a direction, and read it as calf cramping specifically, in a squad averaging about nineteen with a junior group inside it averaging sixteen. It doesn’t automatically transfer to a hamstring.

The second is going harder than the rest of your week supports. In a prospective study of a 56 kilometer ultramarathon, the adult runners who cramped had run the first half faster, and the two groups turned out matched on recent marathon personal bests. Fitness held still and the pacing still separated them. That same study found pre-race training duration and frequency did not distinguish the groups. So this is not a fitness problem, and an evidence-based review states plainly that well-trained athletes still develop these cramps.

Where fueling and hydration actually fit

This is the part of the conversation where I come in, so I want to be precise about it.

The one trial that tested it directly used a carbohydrate and electrolyte beverage during an artificial calf-fatiguing circuit, in thirteen moderately active men, not athletes, each tested twice. In the other trial they drank nothing at all. In the seven who cramped in both trials, the drink more than doubled the time before cramping started. Across all thirteen, it did not change how many cramped. Sixty-nine percent still cramped in the end while hydrated and supplemented with electrolytes.

What’s left lines up with the pacing finding. An athlete who is under-fueled produces the same output at a higher relative cost, so fueling well changes what an effort costs and therefore where the limit sits. That reasoning is something I have witness and seen first-hand and not a specifically measured finding, though the pacing half of it is above.

And separately: show up to hot days already topped up. In 21 male youth soccer players averaging 17.1 years old, fourteen were already dehydrated before training. The general recommendation puts the threshold at a weight loss during training of two percent of body weight, below which performance and thermoregulation start to suffer. Once that occurs the increased effort needed can be a potential factor in cramp risk.

What to do when a cramp actually hits

There are essentially two categories and they are treated differently.

For a cramp related to muscle overload or fatigue, the stated treatment is rest and passive static stretching of the affected muscle until the cramp releases. Passive is doing real work there. It means the stretch is applied to the muscle rather than produced by it, so this is not the moment to push against a locked calf.

For a cramp tied to heavy sweating and a suspected whole-body sodium deficit, sodium in fluid or food is appropriate, in appropriate amounts.

Appropriate is the keyword, as the amount is going to be different for everyone based on how much sodium they are losing in their sweat. Replacing heavy sweat losses entirely with plain water can push blood sodium too low, which is the direction the football study above points. This carries a bit of a risk and potentially create a situation called hyponatremia where the sodium concentration really drops and can be a real health concern.

That’s not a scare line. It is why the guidance specifies a suspected deficit and not simply heavy sweating.

Two products can help to alleviate cramps in the moment as well when they occur. The first one is the age-old pickle juice we’ve all been told about forever. The other is a fairly popular product called Hot Shot and similar related products. What makes these products work though isn’t their sodium concentration. They target the nerves in the muscles specifically through the acid/vinegar in pickle juice and the capsaicin/chili pepper in Hot Shot. Those things block the nerves a little bit to allow the muscle to release and relax again. There are other products out there too with similar mechanisms but these are the two most popular.

What this means for you this season

Know the history. If you have already gone down with a calf cramp this season, you’re carrying something a teammate who hasn’t isn’t. Raised odds are not a guarantee and nobody is saying it will happen again. It does mean a plan is worth more to them than to the player beside them.

Watch the week, not just the match. Two matches a week in continuing heat, with club on top of high school, is a bigger week than August was, and the pace that felt normal six weeks ago is a bigger ask now. Pick a first-half pace that could be repeated in the second.

Fuel and hydrate for the conditions, and replace heavy losses with more than plain water. Itchanges what the same effort costs.

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Frequently Asked Questions

Why does my athlete keep cramping even though they drink plenty of water? In 350 college athletes across 11 sports, sweat composition did not separate athletes with a cramping history from those without, with American football the exception. What has separated them in prospective studies is a prior history of calf cramping in that same muscle, and working harder than the rest of their week supported. Hydration still matters, for performance and for safety. What the studies keep failing to find is a difference in sweat composition between crampers and non-crampers. What does move is how hard an effort feels, which is where fueling for the week’s actual load comes in.

Are electrolyte supplements worth it for cramping? For prevention, the evidence is relatively weak. In the one trial that tested it, thirteen men were each tested twice. The drink more than doubled how long the seven who cramped in both trials lasted, and across all thirteen it did not change how many cramped. Sodium still matters for a heavy sweater in September heat, mostly as replacement after big losses. While it can’t guarantee avoiding a cramp it can help maintain sodium balance and prolong/decrease the rate of the cramp popping up.

Is cramping a sign my athlete isn’t fit enough? In short, no. In the ultramarathon study, training duration and frequency didn’t separate the athletes who cramped from those who didn’t, and an evidence-based review states that well-trained and conditioned athletes still develop these cramps. From the fitness perspective it’s when pushing beyond what is ‘normally’ done. What that level of normal is can vary widely so even fit athletes can push themselves too hard sometimes and result in the increased odds of a cramp.

How do I know whether this is worth working with a sports dietitian on? The pattern worth acting on is recurrence plus a heavy competitive load. If your athlete has gone down more than once this season, in the same muscle, and their week now has more matches in it than their preseason prepared them for, that situation has real opportunity and challenges in it. That’s what the free 15-minute Discovery Call is for to discuss where the improvements could be.

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If you or your athlete are cramping in the second half despite drinking everything handed to you on the sideline, that’s exactly what the free 15-minute Discovery Call walks through. We can discuss where some of those challenges are stemming from and how we could build a plan to combat that.  Book Your Discovery Call

Jay Short, MS, RD, CSSD is a Registered Dietitian and Board Certified Specialist in Sports Dietetics, and co-owner of Rise Nutrition, specializing in sports dietetics for competitive athletes. He works with US Soccer (all 27 teams), the Columbus Blue Jackets (NHL), and athletes across MLS, collegiate, and club programs.

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References

1. Stofan JR, Zachwieja JJ, Horswill CA, Murray R, Anderson SA, Eichner ER. Sweat and sodium losses in NCAA football players: a precursor to heat cramps? https://pubmed.ncbi.nlm.nih.gov/16521848/

2. Miller KC, McDermott BP, Yeargin SW. Sweat Characteristics of Cramp-Prone and Cramp-Resistant Athletes. https://pubmed.ncbi.nlm.nih.gov/32335535/

3. Szymanski M, Miller KC, O’Connor P, Hildebrandt L, Umberger L. Sweat Characteristics in Individuals With Varying Susceptibilities of Exercise-Associated Muscle Cramps. https://pubmed.ncbi.nlm.nih.gov/35482541/

4. Horswill CA, Stofan JR, Lacambra M, Toriscelli TA, Eichner ER, Murray R. Sodium balance during U. S. football training in the heat: cramp-prone vs. reference players. https://pubmed.ncbi.nlm.nih.gov/19777422/

5. Summers KM, Snodgrass SJ, Callister R. Predictors of Calf Cramping in Rugby League. https://pubmed.ncbi.nlm.nih.gov/23774284/

6. Schwellnus MP, Allie S, Derman W, Collins M.Increased running speed and pre-race muscle damage as risk factors for exercise-associated muscle cramps in a 56 km ultra-marathon: a prospective cohort study. https://pubmed.ncbi.nlm.nih.gov/21402566/

7. Miller KC, McDermott BP, Yeargin SW, Fiol A, Schwellnus MP. An evidence-based review of the pathophysiology, treatment, and prevention of exercise-associated muscle cramps. https://pubmed.ncbi.nlm.nih.gov/34185846/

8. Casa DJ, DeMartini JK, Bergeron MF, Csillan D, Eichner ER, Lopez RM, Ferrara MS, Miller KC, O’Connor F, Sawka MN, Yeargin SW. National Athletic Trainers’ Association Position Statement: Exertional Heat Illnesses. https://pubmed.ncbi.nlm.nih.gov/26381473/

9. Jung AP, Bishop PA, Al-Nawwas A, Dale RB. Influence of Hydration and Electrolyte Supplementation on Incidence and Time to Onset of Exercise-Associated Muscle Cramps. https://pubmed.ncbi.nlm.nih.gov/15970952/

10. Williams CA, Blackwell J. Hydration status, fluid intake, and electrolyte losses in youth soccer players. https://pubmed.ncbi.nlm.nih.gov/22645198/