L’key takeaway: Cramps are mainly caused by muscle fatigue, not just a lack of water or salt. Train on descents and climbs, gradually extend your runs, and test your gels during training. If a cramp strikes, stop, gently stretch the muscle, then start again by walking. Sudden or persistent pain requires prompt medical attention.
A cramp gives no warning. It can seize a calf halfway down a descent, when you thought you could keep up your pace without any problem. It’s not always clear how to prevent cramps on trail runs or what to do when they strike. In this article, you’ll find a practical approach, from training to the gel you take during a race, to understand what’s happening in your muscles and act at the right time.
Contents
Why do cramps occur on trail runs?
Cramps don’t have a single cause, and water or salt don’t explain everything. Above all, muscle fatigue disrupts its nerve control: the signals that make it contract and those that make it relax are no longer balanced. An effort that’s longer or more intense than usual tires the muscles and makes cramps more likely. The risk increases when the effort goes beyond what your legs are used to, and descents are often underestimated: muscles brake as they lengthen under tension, which tires them more than running on flat ground. In a 161 km ultra, 14.3% of runners experienced a cramp, showing that even the best-prepared runners aren’t immune.
To avoid sudden jolts, it’s crucial to know how to adjust your pace on the trail: easing off as soon as the descent begins is one of the most effective ways to protect your calves.
What’s normal during a long effort, and what isn’t
A brief cramp near the end of an ultra is common. In some endurance events, around a quarter of participants experienced one. In a 161 km race, those who had experienced one before were more likely to be affected. This doesn't mean you failed to prepare: a cramp lasting a few seconds on a downhill near the end of a long effort is something to note, not a catastrophe. L’important thing is knowing how to tell what’s harmless from what needs attention.
For proper stretching techniques, see our article on stretching after running, then compare your cramp with these signs:
- It goes away as soon as you stop and gently stretch the muscle. This is the most common case, and it’s harmless.
- Severe pain that persists after the cramp should prompt you to see a doctor within the next few days.
- A sudden, stabbing pain that makes it hard to move, or even impossible: see a doctor without delay.
How to train so you don’t get caught off guard
The real key to preventing cramps is preparation. Train on hills, descents, and trails similar to those on your race course, and gradually increase the length of your runs. Unfamiliar descents tire your muscles more, as you’ll notice from the first few kilometers on new terrain. Also, plan to walk for 10 to 15 minutes, then jog easily before each run: see our article on the warm-up routine before a trail race to structure this phase.
To avoid being caught off guard by cramps, supplement your runs with three strategies:
- Add strength training: squats, lunges, deadlifts, and exercises where you control the downward phase of the movement. To work on this braking action, learn how to improve at trail running effectively.
- Plan to rest after a hard session, and ease off if fatigue sets in or your sleep gets worse.
- Test the foods and drinks you plan to have during the race in training, and stick with the ones you tolerate well. To choose and dose your energy gels properly, try them on a long run.
Eating and drinking during a race without putting yourself at risk
Drinking regularly matters more than drinking a lot on race day. Sodium is no guarantee: losses vary from person to person, and salt tablets don't always prevent cramps. It's best not to wait until race day to try your tablets or isotonic drink. For a complete strategy before, during, and after exercise, see our guide to trail running nutrition. In the meantime, here are some basic guidelines to try in training:
| Criterion | Run under 1 h 30 | Exercise lasting over an hour |
|---|---|---|
| Drink | Rich in minerals and vitamins, it may be enough | With carbohydrates and minerals, it helps you sustain your effort |
| Carbohydrates per hour | N/A | 30 to 60 g, adjust according to the duration and your tolerance |
| Gel timing | N/A | Half an energy bar or one gel every 25 to 35 minutes, to test |
These guidelines aren't set in stone: every runner responds differently to exertion and heat. Test, adjust, and note what works for you on long runs before race day.
What to do when a cramp hits on the trail
Stop and gently stretch the muscle until the cramp eases. For a calf cramp, carefully pull your toes toward your knee. Finishing a climb isn't worth having a locked-up muscle for the next few kilometers. Most cramps pass within a few minutes if you don't push through them.
To get going again without starting from scratch, keep these three points in mind, and to pace yourself, see how to pace yourself on a trail run:
- Set off again only once the pain has clearly eased: most cramps pass within a few minutes.
- Then resume gently, walking first, and don't start climbing again right away.
- Avoid quinine: it can cause side effects and does not shorten the duration of the cramp.
When should you seek medical attention?
After prolonged exertion, tea- or cola-colored urine, unusual weakness, or pain much worse than expected may indicate rhabdomyolysis, a serious muscle injury. Seek immediate medical attention if this happens. To reduce the risk beforehand, see how to hydrate properly before exercise.
If the pain doesn’t go away after a few days, limits your movement, or remains severe after the cramp, seek medical advice in the following days. Also consult a doctor if the cramps keep coming back or disrupt your sleep. Sudden stabbing pain that makes it hard to move may be a muscle tear: stop exercising and get examined. If in doubt, make an appointment: a quick visit is better than a month off.
Muscle fatigue is the main cause of cramps, and preparation matters most. Train on descents, gradually increase the length of your runs, test your gels during training, and stay hydrated. Here’s your next practical step: take on a proper descent during your next run, and note when your calves start to tighten. To run better equipped, check out soft flasks and cups Kinetik, designed for hassle-free hydration on all terrain.
FAQ
What deficiency causes cramps?
No deficiency can be said to cause cramps for certain: an exercise-related cramp doesn’t prove a magnesium or salt deficiency. Cramps can have several causes, including muscle fatigue. During a race, first consider what your legs have been through before looking for a deficiency to address.
What’s the best anti-cramp remedy?
No product can guarantee that you won’t get a cramp. The best approach is simple: stop, gently stretch the muscle until it releases, and don’t use quinine for exercise-related cramps. Pickle juice hasn’t been proven effective in real-world racing conditions either.
What’s the old-fashioned remedy for muscle cramps?
The old-fashioned remedy is to gently stretch and massage the muscle. Pickle juice reduced the duration of a laboratory-induced cramp by about 37% after 1 ml. This trial does not prove that it works against trail-running cramps in real-world conditions.
How can you avoid cramps during a marathon?
To avoid cramps during a marathon, train for the race distance and intensity, and warm up before the start. Set off at a controlled pace, drink in moderation, and test your race nutrition during training. There’s nothing magical about it: consistent preparation makes all the difference.