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. Here are 7 of them ranked by how well the research supports them, including two that get recommended all the time on thin evidence.
1. Don't race faster than you've trained
This is the best-supported fix of the lot, and it costs nothing.
Martin Schwellnus and colleagues studied exercise-associated muscle cramp across Ironman and ultra-distance events. The strongest predictors were a personal history of cramping and racing harder than training had prepared the athlete for. Blood electrolyte levels and hydration status didn't reliably separate the crampers from everyone else.
The current best explanation is altered neuromuscular control. Fatigue upsets the balance between muscle spindle excitation and Golgi tendon organ inhibition, the motor neurone keeps 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 gets 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.
Neuromuscular fatigue is specific. A muscle that has repeatedly worked near its limit can take more before reflex control breaks down. It's slow and unglamorous, and it's by far the most reliable long-term fix.
What to do: put your cramp-prone station at the end of a session, once 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 loss is only part of the story, though the evidence for it is real. In one subgroup, athletes with high sweat rates and salty sweat training in the heat, sodium replacement does seem to help.
Lau and colleagues found that an electrolyte drink taken during exercise delayed the onset of electrically induced cramp compared with plain water. It's a controlled lab finding, short of a race result, and it points in a useful direction.
What to do: if you finish sessions with salt crusted on your kit, or you mostly cramp in hot conditions, take sodium during longer sessions. Electrolyte+ (£19.99 for 20 servings, £1 a serve) covers the electrolyte side with 1500mg of electrolytes per stick. Our Hyrox hydration strategy guide covers how much and when.
4. Stretch the cramping muscle, immediately
This one's treatment, and 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. Nobody really disputes 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
It's odd, well studied and works for reasons that surprise most people.
Miller and colleagues induced cramps in dehydrated subjects and found that a small amount of pickle juice, around 70ml, ended them roughly 45% faster than water. It worked 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 switch off the overactive motor neurone, so the effect runs through the nervous system.
What to do: keep a small bottle in your race bag and sip 60-75ml at the first twinge. It shortens a cramp once it's started, and it has no preventive effect.
6. Fix your sleep before your supplement stack
Lack of sleep raises neuromuscular fatigue and lowers the point at which control breaks down. Cramp is mainly a fatigue and control problem, so chronically short sleep is a plausible contributor, and a free one to fix.
Direct trial evidence linking sleep to cramp is thin, so treat this as reasoning from mechanism.
What to do: protect sleep in race week harder than any other part of the taper. Most athletes will get more from that than from anything in a tub.
7. Be sceptical about magnesium
Magnesium is the most commonly recommended cramp remedy and has the weakest evidence of anything here.
Randomised trials of magnesium for muscle cramp, mostly in older adults and in pregnancy, have largely come back negative or inconclusive. There's very little good evidence on exercise-associated cramp in trained athletes.
Magnesium has real uses. Correcting a genuine deficiency matters, and deficiency is fairly common. Calling it a cramp cure is where the evidence runs out.
What to do: if your diet is low in magnesium, fix that on its own merits. Keep your expectations low for cramp, and keep your focus on points 1 and 2, which will make the difference.
FAQ
Is cramping caused by dehydration?
Sometimes, partly. Studies comparing crampers with non-crampers in the same race have generally found no consistent difference in hydration status or blood electrolyte levels. Dehydration probably plays a part 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 push past the intensity you've trained for. That's the classic pattern, and it points straight at pacing.
How much sodium should I take during a Hyrox race?
For a race under 90 minutes in a normal indoor venue, most athletes don't need sodium during the event itself. Getting fluid and sodium right in the 2-3 hours before the start matters more. If you're a heavy sweater or racing somewhere hot, put sodium in your pre-race drink.
Does stretching before a race prevent cramp?
There's no good evidence that it does. Stretching works as treatment once a cramp starts. Use your warm-up to raise muscle temperature and rehearse race intensity.
What about lactic acid, does that cause cramp?
No. Lactate is a fuel, and it clears within minutes of stopping. Acidosis adds to fatigue and to the burning feeling in hard efforts, which is a separate problem with separate solutions. Lactate buffering is the approach that targets it. Our Lactic Acid Buffer (£29.99 for 30 servings) is made for that burn, and cramp is a different problem.
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 clearly dosed supplements for athletes who train with intent. Every ingredient and dose is on the label. See the range.