Muscle Cramps During Exercise: Is It Really Electrolytes?
A runner necks an electrolyte sachet at every aid station, tapes a salt patch to her forearm before the gun, and still seizes up in her left hamstring at kilometre 30. She did everything the cramp-prevention industry tells her to do, and it happened anyway. That gap between the advice and the outcome is where the electrolyte theory of cramping starts to fall apart.
Most exercise-associated muscle cramps aren't caused by dehydration or low electrolytes. The strongest evidence points to neuromuscular fatigue: a tired muscle's nerve signalling misfires, usually late in a hard or unfamiliar effort. Stretching the cramping muscle is still the fastest way to end one, and pacing prevents more cramps than salt tablets do.
Quick Overview
What actually causes muscle cramps during exercise?
An exercise-associated muscle cramp is a sudden, painful, involuntary contraction in a muscle that's already working hard, and the evidence increasingly points to the nervous system rather than the bloodstream. Schwellnus proposed that fatigue disrupts the normal balance between two reflex loops: one from the muscle spindles, which excites the motor neurons, and one from the Golgi tendon organs, which normally inhibits them (Schwellnus, Br J Sports Med, 2009). Push a muscle hard enough for long enough and that balance tips toward excitation. The motor neuron starts firing on its own, and the muscle locks up.
This lines up with where cramps actually happen. They cluster late in a race or a match, in muscles crossing two joints (the hamstrings, the calves, the small muscles that stabilise the arch of the foot), and in athletes working harder or longer than their training has prepared them for (Schwellnus, Br J Sports Med, 2009). A fast bowler cramping in his calves in the 90th over of a hot afternoon in Chennai and a footballer cramping in stoppage time in Manchester are showing the same pattern: a nervous system that's run out of road, not a body that's run out of salt.
Why doesn't the electrolyte theory hold up?
It doesn't hold up because the studies that looked for a difference between cramping and non-cramping athletes mostly didn't find one. In one of the clearest field tests of the idea, Schwellnus and colleagues drew blood from Ironman triathletes and ultra-distance runners immediately after cramping and compared it with non-cramping finishers: serum sodium, potassium, calcium and magnesium were not different between the two groups, and hydration status wasn't either (Schwellnus et al., Br J Sports Med, 2004).
A 2018 systematic review went further, working through 69 papers on the two competing explanations. It concluded that the neuromuscular mechanism was the more compelling of the two, and that the dehydration and electrolyte-depletion hypotheses lacked the experimental support the sports nutrition industry has built around them (Giuriato et al., J Electromyogr Kinesiol, 2018). A 2022 evidence-based review of the whole field reached the same place: altered neuromuscular control is now the leading explanation for exercise-associated cramping in otherwise healthy athletes, with dehydration and electrolyte loss demoted to possible contributing factors rather than the cause (Miller et al., J Athl Train, 2022).
What actually stops a cramp once it starts?
Stretching the cramping muscle, hard and immediately, is still the most reliable way to end one, and it works through the same reflex system that caused the cramp in the first place. Pulling the tendon taut fires the Golgi tendon organ, which sends an inhibitory signal back to the motor neuron and interrupts the runaway firing (Miller et al., J Athl Train, 2022). That's a mechanical, reflex-based fix, not a nutritional one, and it works whether or not the athlete has had a sip of water in the last hour.
One study makes the case unusually well. Miller and colleagues induced cramps electrically in dehydrated participants, then gave some of them pickle juice. The cramps stopped in an average of 85 seconds, and the authors were blunt about what that timing means: 85 seconds isn't enough time for anything in the drink to leave the stomach, cross the gut wall, and reach the cramping muscle. Gastric emptying of that volume of fluid takes around 30 minutes at rest. The relief had to come from a nerve reflex triggered in the mouth and throat, not from replaced fluid or electrolytes (Miller et al., Med Sci Sports Exerc, 2010). It's a strange result to sit with: something in the mouth switching off a cramp in the calf faster than the drink could reach the stomach, let alone the muscle.
Worth separating two different claims here. Stretching relieves an active cramp fast. It doesn't reliably prevent future ones: a study that had athletes stretch and then tested how much electrical stimulation it took to trigger a new cramp found no real difference between the stretched and unstretched groups (Panza et al., J Athl Train, 2017). Treat a cramp with stretching. Don't expect a pre-race stretching routine to stop the next one from happening.
Do electrolytes matter at all?
Yes, just not as the primary cramp mechanism. Sodium is still central to hydration and heat tolerance, and a 2025 review of sodium intake in athletes found real evidence that it can help in some cramping cases: eccentric muscle damage combined with a rapid drop in plasma sodium concentration appears to lower the threshold for cramping in some people, and replacing sodium during long, hot efforts may help prevent that drop (McCubbin, Performance Nutrition, 2025). The same review is candid that cramping looks like a multifactorial syndrome, not a single-cause problem, and that other studies have found no relationship between sweat composition or plasma sodium and who cramps and who doesn't.
The honest summary: electrolytes are one plausible contributor for some athletes in some conditions, most relevant in long, hot, heavy-sweating efforts, but they're not the dominant mechanism the sports drink and electrolyte-tablet marketing implies. Hydration still matters in its own right, for heat regulation and for performance generally; that's a separate question from what actually triggers a cramp.
Reducing cramps: pacing beats salt tablets
If fatigue and unfamiliar load are doing most of the work, the fix is training load, not a supplement aisle. The clearest risk factors for exercise-associated cramping are racing faster than trained pace, a longer history of cramping, and doing more of an unaccustomed movement than the body is ready for (Schwellnus, Br J Sports Med, 2009). A marathoner in Mumbai who has never run above 28°C (82°F) and then races a hot October event, or a cricketer who bowls double his usual overs in a single spell, is loading a system that hasn't adapted, regardless of how much sodium is on board.
Three things move the needle more than salt tablets: build the specific muscular endurance the event demands, rather than just general fitness; practise at or near race intensity and duration in training, so the nervous system has met that level of fatigue before; and pace conservatively enough in the first two-thirds of a long effort that the last third doesn't ask the body for something it's never done. None of that rules out drinking to thirst and replacing sodium sensibly in heat. It just means treating cramp prevention as a training problem first.
Cramping that's frequent, severe, doesn't ease with stretching, or comes with swelling, marked weakness or cramping outside of exercise is worth a doctor's visit, to rule out causes unrelated to sport.
The Fueletics Perspective
The reason the electrolyte story persists isn't the evidence. It's that it's an easier problem to sell a solution for. Fatigue and pacing require training changes and patience; a sachet is a five-second fix at an aid station. The research doesn't support that trade.
What I actually watch for with the athletes I work with is training load relative to what the body has adapted to, not sodium intake. Someone who's cramping in the same muscle, in the same part of every long session, almost always has a pacing or conditioning gap, not a mineral deficit. Fixing the number that's actually wrong takes individual data, not a generic electrolyte protocol; if you want yours worked out properly, start with a Fueletics assessment.
FAQ
Does magnesium stop muscle cramps?
There's no strong evidence that oral magnesium supplementation prevents exercise-associated cramps in athletes with normal magnesium status. Where magnesium status is genuinely worth checking, RBC (red blood cell) magnesium is the relevant marker, not serum magnesium, which doesn't reflect the body's stores accurately.
Are muscle cramps a sign of dehydration?
Not reliably. Field studies comparing cramping and non-cramping athletes at the same events have generally found no difference in hydration status between the two groups (Schwellnus et al., Br J Sports Med, 2004).
Should athletes take salt tablets before a race to prevent cramping?
Salt tablets haven't been shown to reliably prevent exercise-associated cramps in athletes without a specific sodium-loss problem. Sodium replacement can still matter for hydration and heat tolerance in long, hot events, and may help some athletes indirectly, but it isn't a general cramp-prevention fix.
Why do cramps happen late in a race and not earlier?
Because the leading mechanism is neuromuscular fatigue, and fatigue accumulates. Cramps cluster in the final stages of long or hard efforts, and in muscles or movements the athlete hasn't specifically trained for at that intensity.
Research References
Schwellnus MP. Cause of exercise associated muscle cramps (EAMC) — altered neuromuscular control, dehydration or electrolyte depletion? Br J Sports Med. 2009;43(6):401–408. doi:10.1136/bjsm.2008.050401
Schwellnus MP, Nicol J, Laubscher R, Noakes TD. Serum electrolyte concentrations and hydration status are not associated with exercise associated muscle cramping (EAMC) in distance runners. Br J Sports Med. 2004;38(4):488–492. PMID: 15273192
Giuriato G, Pedrinolla A, Schena F, Venturelli M. Muscle cramps: A comparison of the two-leading hypothesis. J Electromyogr Kinesiol. 2018;41:89–95. doi:10.1016/j.jelekin.2018.05.006
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. J Athl Train. 2022;57(1):5–15. doi:10.4085/1062-6050-0696.20
Miller KC, Mack GW, Knight KL, Hopkins JT, Draper DO, Fields PJ, Hunter I. Reflex Inhibition of Electrically Induced Muscle Cramps in Hypohydrated Humans. Med Sci Sports Exerc. 2010;42(5):953–961. doi:10.1249/MSS.0b013e3181c0647e
Panza GA, Stadler JT, Murray D, Lerma N, Barrett T, Pettit-Mee R, Edwards JE. Acute Passive Static Stretching and Cramp Threshold Frequency. J Athl Train. 2017;52(10):918–924. doi:10.4085/1062-6050-52.7.03
McCubbin AJ. Sodium intake for athletes before, during and after exercise: review and recommendations. Performance Nutrition. 2025;1(1):11. doi:10.1186/s44410-025-00011-9
