Muscle Cramps in Running: What the Evidence Says
The evidence on muscle cramps in running points mostly at fatigue: the runners who cramp tend to be the ones who have cramped before, went out faster than usual, or did more muscle damage, not the ones who lost the most salt or water. For treating a cramp that has already started, gentle stretching is the only fix with consistent support; everything else, from pickle juice to magnesium, ranges from “small lab effect” to “no effect found”.
That’s the short version. The longer one is more useful, because cramp research is full of small studies that get quoted as if they settled things. Here’s what each piece actually shows, and how much weight it can carry.
Why is cramp research so hard to trust?
Because cramps won’t turn up on cue. You can’t book a runner into a lab and guarantee their calf locks at minute 40, so researchers either watch big races and compare crampers with non-crampers after the fact, or they trigger cramps artificially with electrical stimulation or hard contractions of a shortened muscle. Ron Maughan and Susan Shirreffs, reviewing the field in 2019, pointed out that these lab-induced cramps may not behave like the ones that hit you at kilometre 35, and that there are probably several types of cramp with different triggers (Maughan and Shirreffs, 2019).
Keep that in mind for the rest of this page. Race studies tell you who cramps. Lab studies tell you what changes an artificial cramp. Neither gives you a clean answer on what stops a real one in a real race.
What do race studies say about who cramps?
Three race studies, on three different kinds of event, landed in the same place.
At an Ironman triathlon, 43 of 210 athletes cramped. Their blood sodium and body-weight change matched the non-crampers. What set them apart was a history of cramping and racing faster than they had planned (Schwellnus et al., 2011).
At the 161 km Western States Endurance Run, 14.3% of runners who answered the survey cramped and another 26.8% reported “near cramping”, the twitchy, about-to-go feeling most ultra runners know. Calves were hit most (54%), then quads (44%) and hamstrings (33%). Crampers were more likely to have cramped in an earlier ultra and had higher blood creatine kinase, a marker of muscle damage. Weight change, sodium supplement use, the rate of sodium taken in supplements and post-race blood sodium did not differ (Hoffman and Stuempfle, 2015).
A separate study of 20 finishers at a 161 km ultra where temperatures reached 39°C found total sodium intake ranged from about 2,500 mg to over 38,000 mg across the day, and still showed no link between how much sodium a runner took and whether they cramped (Hoffman et al., 2015).
Put those together and a profile appears. The runner most likely to cramp at the Borneo International Marathon isn’t the one who forgot a salt tablet. It’s the one who cramped there last year, went through halfway two minutes up on plan, and is now asking legs trained on flat roads to do more than they’ve done before.
Does dehydration play any part?
It may delay a cramp, but it doesn’t explain most of them. The cleanest test is an old one: 13 men with a history of cramps did a calf-fatiguing protocol at 37°C and 60% humidity, once drinking a salted carbohydrate-electrolyte drink to match sweat loss, once drinking nothing. In the drink trial, nine still cramped, against seven when they drank nothing. Among the seven who cramped both times, the drink pushed the onset back from about 15 minutes to about 37 (Jung et al., 2005).
That’s a real effect on timing and no effect on whether it happened. Sixty-nine percent of the men cramped while fully hydrated and supplemented. Those lab conditions are hotter than a typical Malaysian race morning, but not by as much as a back-of-pack marathoner finishing at 10 am in Kuantan would like.
Maughan and Shirreffs leave some room for a dehydration-type cramp, mainly from industrial records of workers in very hot jobs, alongside the fatigue type. That’s the fairest reading: two or more mechanisms, with fatigue behind most of what endurance athletes report.
Common cramp remedies, graded by the evidence
This is where most articles get loose. Here’s each remedy with the best evidence we could find, and what that evidence actually tested.
| Remedy | Best evidence | What it showed | Our read |
|---|---|---|---|
| Gentle static stretching | Evidence-based review (Miller et al., 2022) | Still the recommended treatment for an acute cramp, until symptoms ease | First thing to do, every time |
| Pickle juice | One lab study in dehydrated men, electrically induced cramps in a small foot muscle (Miller et al., 2010) | Cramps about 49 seconds shorter than after the same small volume of water (85 vs 134 seconds); too fast for any absorbed salt to explain | Plausible reflex effect, small evidence base |
| Spicy or sour “TRP” shots | One randomised, double-blind crossover study, 39 people, voluntarily induced calf cramps (Craighead et al., 2017) | Longer contraction before cramp, roughly half the cramp intensity on EMG, slightly less soreness after | Most promising of the “drink something” options; not tested mid-race |
| Electrolyte drink, matched to sweat | 13 men, induced calf cramps in heat (Jung et al., 2005) | Delayed onset; 69% still cramped | May buy time, won’t prevent |
| Sodium supplements in ultras | 161 km ultramarathon field studies (Hoffman and Stuempfle, 2015; Hoffman et al., 2015) | No difference between crampers and non-crampers | Not a cramp tool on the current evidence |
| Magnesium | Cochrane review, 11 trials (Garrison et al., 2020) | No meaningful benefit for cramps in older adults; no trials on exercise cramps at all | Unsupported for runners |
| Bananas and potassium | No controlled trials on exercise cramps found in our search | Untested | Fine as food, not as a cramp plan |
Two patterns stand out. The options with any support act fast and work through nerves, not through blood chemistry. And none of them has been tested on a runner cramping on the Penang Bridge with 10 km to go, which is the situation everyone actually cares about.
Why would a sour drink work faster than salt?
Because it doesn’t need to be absorbed. In the pickle juice study, cramps eased within about a minute and a half, long before the drink could have left the stomach and changed anything in the blood. The working idea is that strong flavours stimulate receptors in the mouth and throat, which dampen the over-excited nerve signal driving the cramp.
That’s a useful fact for anyone who has watched a running club WhatsApp group argue about whether salt tablets “kick in” mid-cramp. On the timescales involved, they can’t.
What does a cramp plan look like without a magic product?
The 2022 review in the Journal of Athletic Training made one point worth taping to the fridge: individual prevention based on your own risk factors is likely to work better than generic advice like “drink more” (Miller et al., 2022). For runners, the risk factors the race studies keep finding are ones you can actually change.
Your history. If you’ve cramped in two of your last three marathons, you are the high-risk group in every study above. Write down where it happened, what the terrain was, and how your pace compared with plan.
Your pacing. Faster-than-planned racing predicted cramps in the Ironman data. A first half that feels embarrassingly easy is the cheapest cramp prevention there is.
Muscle-specific load. Cramps cluster in the muscles that did the most unaccustomed work, which is why creatine kinase keeps showing up. If your race has a long descent or a bridge climb, train that specific load. Downhill repeats on the Bukit Gasing or Bukit Kiara trails will do more for a hilly race than any capsule.
A sensible fluid plan. Not because it prevents cramps, but because overdrinking brings its own problems in long events. Our guide to dehydration vs hyponatremia in ultras covers why.
A cramp drill. Stop, stretch the muscle gently until it lets go, walk a little, then restart slower. If you want to carry something sour, test it in training first, because a mouthful of vinegar at kilometre 30 is a bold new experience.
What would change our view?
A proper field trial would. Nobody has yet randomised a large group of marathon or ultra runners to a cramp intervention and counted real race cramps. Until someone does, the honest position is that cramps are mostly a fatigue problem with more than one cause, and the remedies with any support are fast-acting and modest.
If you want the practical, race-day version of this, read Leg Cramps on Long Runs. For how heat and sweat fit into the picture, start from our running hydration and electrolytes guide, and for a first-hand account of cramping after a near-fall, see the TMBT 50K race report.
References
- Maughan RJ, Shirreffs SM (2019). Muscle cramping during exercise: causes, solutions, and questions remaining. Sports Medicine, 49(Suppl 2), 115-124. doi:10.1007/s40279-019-01162-1
- Schwellnus MP, Drew N, Collins M (2011). Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: a prospective cohort study in 210 Ironman triathletes. British Journal of Sports Medicine, 45(8), 650-656. doi:10.1136/bjsm.2010.078535
- Hoffman MD, Stuempfle KJ (2015). Muscle cramping during a 161-km ultramarathon: comparison of characteristics of those with and without cramping. Sports Medicine – Open, 1(1), 24. doi:10.1186/s40798-015-0019-7
- Hoffman MD, Stuempfle KJ, Valentino T (2015). Sodium intake during an ultramarathon does not prevent muscle cramping, dehydration, hyponatremia, or nausea. Sports Medicine – Open, 1(1), 39. doi:10.1186/s40798-015-0040-x
- Jung AP, Bishop PA, Al-Nawwas A, Dale RB (2005). Influence of hydration and electrolyte supplementation on incidence and time to onset of exercise-associated muscle cramps. Journal of Athletic Training, 40(2), 71-75. PMID 15970952
- Miller KC, McDermott BP, Yeargin SW, Fiol A, Schwellnus MP (2022). An evidence-based review of the pathophysiology, treatment, and prevention of exercise-associated muscle cramps. Journal of Athletic Training, 57(1), 5-15. doi:10.4085/1062-6050-0696.20
- Miller KC, Mack GW, Knight KL, et al. (2010). Reflex inhibition of electrically induced muscle cramps in hypohydrated humans. Medicine & Science in Sports & Exercise, 42(5), 953-961. doi:10.1249/MSS.0b013e3181c0647e
- Craighead DH, Shank SW, Gottschall JS, et al. (2017). Ingestion of transient receptor potential channel agonists attenuates exercise-induced muscle cramps. Muscle & Nerve, 56(3), 379-385. doi:10.1002/mus.25611
- Garrison SR, et al. (2020). Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews, 9, CD009402. doi:10.1002/14651858.CD009402.pub3
