Are you training for a trail race? Cramps mostly appear beyond 30 km, on 40 to 80 km trail races, and even more on ultras such as 100 km races. To prevent cramps in trail running, the most effective approach is to prepare your muscles for the downhills and the duration, and to manage your pace from the start. Salt and water matter, but less than people think.
The short answer
- In trail running, cramps mainly come from muscle fatigue, made worse by downhills that heavily load the quads and calves.
- Taking salt capsules did not prevent cramps in a study on a 161 km ultra.
- Strength training, downhill training and a cautious start are your best prevention levers.
- Pickle juice may shorten a cramp that has already set in, but its preventive effect has not been shown.
- If a cramp hits: walk, gently stretch the muscle, then build back up gradually.
Contents
- What is a muscle cramp in trail running?
- Which muscles cramp most in trail running?
- Why are cramps more common in trail and ultra running?
- 6 tips to prevent cramps in trail running and ultras
- What to do if you cramp during a trail race
- Prevent cramps on the trail with RunMotion Coach’s strength module
- FAQ: cramps in trail running and ultras
What is a muscle cramp in trail running?
A cramp is an involuntary, painful contraction of a muscle or muscle group. It comes on suddenly and can last from a few seconds to several minutes.
Trail runners are particularly exposed on steep climbs and technical descents, where muscles work at their limit. Night cramps can also appear after the race, when muscles are exhausted and recovery has not yet done its job.
Which muscles cramp most in trail running?
Calves
On climbs, the calves push the body upwards. On descents, they stabilise and cushion every footstrike. This constant demand makes them one of the most affected areas.
Quads
The quads absorb a large share of the impact on descents. They work as brakes, in eccentric mode: the muscle lengthens while contracting. This type of effort quickly tires and damages the fibres, which explains thigh cramps in the second half of a mountain race.
Hamstrings
The hamstrings help with propulsion and stability on rough terrain. Over long hours of effort, they eventually tire too, especially if they are weak compared with the quads.
Feet, back and abs
The small muscles of the feet work on every step over rocks and roots. The back and abs hold your posture on unstable terrain. Cramps there are rarer, but possible once fatigue sets in.
Why are cramps more common in trail and ultra running?
The best-supported explanation today is neuromuscular: as a muscle tires, the nervous control that regulates its contraction is disrupted and it ends up contracting on its own (Schwellnus, 2009). Trail running combines everything that drives this fatigue: hours of effort, repeated descents and often heat.
A large study in Ironman triathletes showed that cramps were associated with a faster race pace and a history of cramping, but not with dehydration or blood sodium (Schwellnus et al., 2011). In a 161 km ultra, researchers also found that taking more sodium during the race did not protect against cramps (Hoffman and Stuempfle, 2015). These studies are observational and do not say hydration is useless, but they suggest not betting everything on salt. A recent review concludes that the causes are multiple and vary between runners (Maughan and Shirreffs, 2019).
On the road, the mechanisms are similar but the context differs: we cover that case in our article on how to avoid cramps during a marathon.
6 tips to prevent cramps in trail running and ultras
1. Add strength and conditioning
Stronger muscles tire more slowly. One or two trail-specific strength sessions a week strengthen your quads, calves, hamstrings, glutes and core. Studies have not yet directly shown that strength training prevents cramps, but it is the lever most consistent with what we know about muscle fatigue.
2. Train on descents
Many trail runners train the climbs and forget the descents. Yet descents are what wear out the quads most. Regularly include downhill sections in your runs, short and at a moderate pace at first, then longer. Your muscles adapt to this eccentric effort and suffer less on race day. Our tips on how to run downhill also help you place your feet more efficiently.
3. Manage your pace from the start
In a long trail race, the first hours shape the end of your race. A start that is too fast, often driven by excitement or the urge to avoid bottlenecks, builds fatigue that will come back later as cramps. Power-hike the first climbs if needed and keep some freshness for the second half. If you have cramped before, be even more cautious.
4. Increase your load gradually
Lengthen your long runs and elevation gain progressively over your build-up, and plan lighter weeks to absorb the work. A training load that rises too fast tires your muscles before the race even starts.
An adaptive plan takes your load and previous sessions into account to dose this progression. Try RunMotion Coach free for 7 days to prepare for your next trail race.
5. Hydrate and adapt to the heat
Drink small amounts regularly, guided by thirst, and increase your intake when it is hot. In an ultra, sodium is still useful to tolerate what you drink and eat over many hours, through sports drinks, gels or salty foods. Just don’t count on it to stop cramps. Always test your strategy in training, especially on your long runs.
6. Choose the right gear
Trail shoes you know, with good grip, limit hesitant footsteps that tire your muscles needlessly. A hydration vest lets you drink and eat regularly between aid stations. Compression socks have not been shown to prevent cramps, but if you feel good in them, nothing stops you wearing them.
What to do if you cramp during a trail race
- Slow down and walk to reduce tension on the affected muscle.
- Gently stretch the muscle: for the calf, lean forward with the affected foot behind you and the heel on the ground; for the quad, bend your knee and bring your heel towards your glutes.
- Massage the area with your hands, or a small roller if you carry one.
- Drink and eat if you have not had anything for a while.
- Start again gradually, alternating walking and easy running before getting back to your rhythm.
And pickle juice? A lab study showed it shortened cramps induced by electrical stimulation. Blood electrolyte levels did not change: the effect seems to come from a reflex triggered in the mouth and throat, not from the salt it supplies (Miller et al., 2010). So it is a possible trick to relieve a cramp that has set in, if you tolerate it. However, there is no evidence that drinking it beforehand prevents cramps.
If you get very frequent cramps, including at rest, or severe muscle pain after a race, see a doctor.
Prevent cramps on the trail with RunMotion Coach’s strength module
To prevent cramps in trail and ultra running, prepare your muscles for the duration and the descents, start cautiously and don’t rely on salt alone. The rest is decided in training, weeks before the start.
RunMotion Coach training plans adapt to your goal and your training load. The strength and conditioning module offers strengthening exercises to prepare your muscles for long efforts and unstable terrain. Balanced leg strength, without forgetting the hamstrings, is a real plus for limiting cramps and injuries.
FAQ: cramps in trail running and ultras
Why do I cramp on descents?
On descents, your quads and calves brake your body on every step. This eccentric work quickly tires and damages muscle fibres. Training regularly on descents helps your muscles adapt.
Do salt capsules prevent cramps in ultras?
Not according to the available studies. In a 161 km ultra, taking more sodium did not protect against cramps. Sodium is still useful to tolerate drinks and food over long hours, but it does not replace muscle preparation.
Does pickle juice work for cramps?
It may shorten a cramp that has already set in, through a reflex effect rather than the salt. However, its preventive effect has not been shown.
At what distance do cramps become a risk in trail running?
They mostly appear beyond 30 km and are more common in ultras. But a shorter race that is very steep or run too fast can also trigger them.
Updated on 30 October 2026.
Sources: Schwellnus, Br J Sports Med, 2009 · Schwellnus et al., Br J Sports Med, 2011 · Hoffman and Stuempfle, Sports Med Open, 2015 · Maughan and Shirreffs, Sports Med, 2019 · Miller et al., Med Sci Sports Exerc, 2010.
