Mavr Sports Nutrition Team
Updated September 28, 2026. 8 min read.
It happens fast. One minute you're running fine, the next your calf seizes up like someone jabbed a knife into your muscle. You stop, you stretch, you massage it, and eventually it releases — but your pace is shot and your confidence is gone.
Running cramps are one of the most frustrating problems in endurance sport. They feel random, but they are not. They have specific causes, and good pacing and fueling can lower your risk.
This is the main driver of muscle cramps during exercise. When you run harder or longer than your legs are trained for, the nerve signals that tell a muscle to contract get stronger and the signals that tell it to relax get weaker. The muscle can lock into a sustained contraction: a cramp. This is why cramps often hit late in races, especially if you started faster than your training supports. Running low on glycogen (stored carbohydrate) makes that fatigue come sooner, which is where nutrition helps.
Sodium loss is a contributing factor, not the main cause. It matters most for heavy or salty sweaters in long, hot events. You lose roughly 400-1,500mg of sodium per liter of sweat, so on a 2-hour run in warm weather you might lose 1,000-3,000mg. If you only drink plain water, you replace the fluid but not the salt.
Sodium helps carry the electrical signals that control your muscles. But runners who cramp in races have not been found to have lower blood sodium than runners who do not. Salt may still help the smaller group of runners with very high sodium losses, but for most runners it is not what sets off a cramp.
Losing more than 2% of your body weight in fluid hurts performance and may add to cramp risk, mostly in long, hot events. It reduces blood volume, meaning less oxygen and fewer nutrients reach your muscles, so they tire sooner.
Nutrition cannot fully fix cramps that come from running faster or longer than you trained for. Pacing and training come first: build long runs and race-pace work gradually, and start races at a pace your training supports. Fueling well delays fatigue, and sodium matters most if you are a heavy or salty sweater.
Light sweater / cool weather
Sodium Target300–500mg/hour
How to Get It1 electrolyte drink or salted snack
Moderate sweater / normal conditions
Sodium Target500–700mg/hour
How to Get ItElectrolyte drink + 1 salt tab or salty food
Heavy sweater / hot weather
Sodium Target700–1,000mg/hour
How to Get ItElectrolyte drink + salt tabs + salted foods
| Sweat Level | Sodium Target | How to Get It |
|---|---|---|
| Light sweater / cool weather | 300–500mg/hour | 1 electrolyte drink or salted snack |
| Moderate sweater / normal conditions | 500–700mg/hour | Electrolyte drink + 1 salt tab or salty food |
| Heavy sweater / hot weather | 700–1,000mg/hour | Electrolyte drink + salt tabs + salted foods |
Since glycogen depletion speeds up neuromuscular fatigue, staying on top of carb intake during long runs helps delay the fatigue that sets up cramps.
The biggest lever is pacing: most late-race cramps come from asking your legs for more than they are trained for. On the nutrition side, keep carbs coming (30-60g per hour past 75-90 minutes), because a fatigued, glycogen-depleted muscle is more cramp-prone than a fueled one. If you are a heavy or salty sweater, also aim for 300-700mg of sodium per hour on long or hot efforts, more if you finish caked in white residue. Dial those in over a few long runs and "random" late-race cramps often become less common.
Setting your sodium and carb targets from your sweat rate and the day's conditions is something Mavr can do automatically. But the approach above (pace to your training, stay fueled, replace sodium if you sweat a lot) is the practical fix, and you can start testing it on your very next long run.
Not really. The "banana prevents cramps" idea comes from the potassium theory, but most running cramps come from muscle fatigue, and potassium loss in sweat is small. A banana has only about 400mg of potassium and almost no sodium. It is still a good carb snack before a run. If you are a salty sweater, add a salted pretzel or an electrolyte drink for sodium.
Repeated cramping in the same muscle (usually calf or hamstring) often means that muscle is working harder than others — possibly due to biomechanics, muscle imbalances, or overcompensation from a previous injury. The nutritional prevention is the same, but you may also benefit from strength training and mobility work on that specific muscle.
Salt tablets do not reliably stop cramps, because most cramps come from muscle fatigue rather than salt loss. They can help heavy or salty sweaters in long, hot events, taken with plenty of water. For most runners, an electrolyte drink mix that provides sodium along with fluid is simpler. A typical salt capsule has about 200-250mg of sodium (some brands up to about 500mg), and 1-3 per hour is common for long runs in warm conditions.
Race intensity is higher than training, which means more sweating, faster glycogen depletion, and greater neuromuscular fatigue. You are also less likely to drink and fuel consistently during a race because of adrenaline and focus on performance. Start at a pace your training supports, and practice your race-day fueling and hydration plan in training.
General guidance for healthy adults, not medical advice. Talk to a doctor or registered dietitian if you have a health condition, take medicines or have special dietary needs.
Lower your cramp risk on long runs. Mavr calculates your carb, sodium, and hydration needs based on your sweat rate and conditions.
Ask Kai, the coach in the app