7 best ways to prevent muscle cramp during endurance races
Cramp ends races. One minute you're holding pace through the lunges, the next your hamstring locks and you're standing at the side of the floor doing maths on your finish time.
The best ways to prevent muscle cramp turn out to be mostly free, mostly boring, and mostly about how you pace and train rather than what you drink. Here are 7 interventions ranked by how well the research supports them, including two that get recommended constantly on thin evidence.
1. Don't race faster than you've trained
This is the single best-supported intervention, and it costs nothing.
Martin Schwellnus and colleagues studied exercise-associated muscle cramp across Ironman and ultra-distance events and found the strongest predictors were a personal history of cramping and racing at an intensity higher than training had prepared the athlete for. Blood electrolyte concentrations and hydration status did not reliably separate crampers from non-crampers.
The current best explanation is altered neuromuscular control. Fatigue disrupts the balance between muscle spindle excitation and Golgi tendon organ inhibition, the motor neurone stays firing, and the muscle locks.
What to do: know your realistic race pace and hold it through the first three stations, when it feels far too easy. Most Hyrox cramping happens between the sled pull and the lunges, and most of it was set up in the first 20 minutes.
2. Train the specific movement to fatigue
If your calves cramp in the lunges, the answer is more loaded lunges under fatigue, not a different drink.
Neuromuscular fatigue is specific. A muscle that has repeatedly worked near its limit tolerates more before the reflex control breaks down. This is slow, unglamorous and by far the most reliable long-term fix.
What to do: put your cramp-prone station at the back end of a session, after you're already tired, at least once a week for 6 weeks. Compromised running blocks do the same job for calves and hamstrings.
3. Replace sodium if you're a heavy or salty sweater
Electrolyte depletion isn't the whole story, and the evidence isn't zero either. There's a subgroup, athletes with high sweat rates and high sweat sodium concentrations training in heat, where sodium replacement does seem to help.
Lau and colleagues found that drinking an electrolyte beverage during exercise delayed the onset of electrically induced cramp compared with plain water. That's a controlled lab finding rather than a race result, but the direction is useful.
What to do: if you finish sessions with visible salt crust on your kit, or you cramp mainly in hot conditions, take sodium during longer sessions. Electrolyte+ (£19.99 for 20 servings, £1 a serve) covers the electrolyte side with a calcium-heavy formula and no artificial sweeteners. Our Hyrox hydration strategy guide covers how much and when.
4. Stretch the cramping muscle, immediately
For treatment rather than prevention, but it's the fastest thing that works.
Passive stretching increases Golgi tendon organ activity, which inhibits the motor neurone that's firing, which stops the cramp. It usually works within seconds. There's no debate about this one.
What to do: for a calf, pull your toes towards your shin with the leg straight. For a hamstring, straighten the leg and hinge forward. Hold until it releases, then walk before you run.
5. Try pickle juice for acute relief
Odd, well studied, and effective for reasons that surprise most people.
Miller and colleagues induced cramps in hypohydrated subjects and found that a small volume of pickle juice, around 70 mL, resolved them roughly 45 per cent faster than water. The effect happened far too quickly for the fluid to have been absorbed and reached the muscle.
The explanation is a reflex: acetic acid stimulates receptors in the mouth and throat that trigger inhibition of the overactive motor neurone. It works on the nervous system, not the muscle.
What to do: keep a small bottle in your race bag. Sip 60 to 75 mL at the first twinge. It won't prevent cramp, it will shorten one.
6. Fix your sleep before your supplement stack
Sleep deprivation raises neuromuscular fatigue and lowers the threshold at which control breaks down. Given cramp is primarily a fatigue and control problem, chronically short sleep is a plausible contributor and a free one to fix.
The direct trial evidence linking sleep to cramp specifically is thin, so treat this as reasoning from mechanism rather than proof.
What to do: protect sleep in race week harder than you protect any part of the taper. Most athletes will get more out of that than anything in a tub.
7. Be sceptical about magnesium
Magnesium is the most commonly recommended cramp remedy and has the weakest evidence of anything on this list.
Randomised trials of magnesium supplementation for muscle cramp, mostly in older adults and in pregnancy, have largely come back negative or inconclusive. There is very little good evidence specific to exercise-associated cramp in trained athletes.
Magnesium has real uses. Correcting a genuine deficiency matters, and deficiency is reasonably common. Treating it as a cramp cure is where the evidence runs out.
What to do: if your diet is low in magnesium, address that on its own merits. Don't expect it to fix cramping, and don't let it distract from points 1 and 2, which will.
FAQ
Is cramping caused by dehydration?
Sometimes, partly. Studies comparing crampers to non-crampers in the same race have generally found no consistent difference in hydration status or blood electrolyte levels. Dehydration probably contributes in hot conditions and in heavy sweaters, but neuromuscular fatigue explains more cases.
Why do I only cramp in races and never in training?
Because races are where you exceed your trained intensity. That's the classic pattern, and it points straight at pacing rather than nutrition.
How much sodium should I take during a Hyrox race?
For a race under 90 minutes in a normal indoor environment, most athletes don't need sodium during the event itself. Getting hydration and sodium right in the 2 to 3 hours before the start matters more. If you're a heavy sweater or racing somewhere hot, take sodium in the pre-race drink rather than trying to drink mid-race.
Does stretching before a race prevent cramp?
No good evidence that pre-race stretching prevents cramping later. Stretching works as treatment once a cramp starts. Use your warm-up to raise muscle temperature and rehearse race intensity instead.
What about lactic acid, does that cause cramp?
No. Lactate is a fuel, not a waste product, and it clears within minutes of stopping. Acidosis contributes to fatigue and to the burning sensation during hard efforts, which is a separate problem with separate solutions. Our Lactic Acid Buffer (£29.99) is built for that burn, not for cramp.
Where to start
If you cramp regularly, work down this list in order. Pace control and specific training will fix more cases than everything else combined. Sodium helps a subgroup. Pickle juice and stretching get you moving again once it's happened.
Interval makes transparently-dosed supplements for athletes who train with intent. Every ingredient and dose is on the label. See the range.