How to Prevent Cramps While Running: A South African Runner's Guide

You're cruising through a long run, the legs feel fine, and then at 30km your calf locks up like a fist and the whole race changes. Running cramps are miserable, and most of the advice out there blames the wrong thing. The truth is more useful than the salt-tablet myth: here's what actually causes running cramps, what the science says really prevents them, and where electrolytes do and don't help on a hot South African long run.

What Actually Causes Muscle Cramps When Running?

Most running cramps are caused by neuromuscular fatigue, not simply by dehydration or a lack of salt, which is the opposite of what most product marketing tells you. The leading scientific explanation is that when a muscle gets tired, the nerve signals controlling it fall out of balance, with too much excitatory drive and too little of the inhibitory braking that normally keeps it relaxed. The muscle then locks into a cramp. A review of exercise-associated muscle cramps found the evidence for this fatigue mechanism is stronger than the evidence for dehydration.

That matters because it changes what you do about it. If cramps were purely an electrolyte problem, a salt tablet would fix everything. Studies where runners cramped despite being hydrated and topped up with electrolytes show it isn't that simple. Fatigue is the bigger lever, which is good news, because fatigue is something your training can directly improve.

How Do You Prevent Running Cramps?

The most effective way to prevent running cramps is to reduce the muscle fatigue that triggers them, by training properly for your distance and pacing the run sensibly. Going out too fast for your fitness is the single most common cramp trigger we see, because it fatigues your legs early and they pay for it later. Build your long runs gradually, condition the specific muscles you're asking to work, and respect the pace your training actually supports.

Two practical habits help a lot. First, don't race a distance your legs haven't rehearsed, because an unprepared muscle fatigues fast. Second, ease off the pace at the first hint of a twinge rather than pushing through, since cramps usually give a warning before they lock. Strength work and consistent long runs do more to prevent cramps than anything you can drink.

There's also some evidence that regularly cramping muscles respond to deliberate stretching in training, not just during a race. Working a little flexibility and calf and hamstring strength into your week conditions the exact muscles that tend to seize, which lifts the fatigue threshold at which they cramp. It's slow, unglamorous work, but it's the kind that actually holds up at 35km when a quick fix won't.

Do Electrolytes and Salt Prevent Cramps?

Electrolytes help with the subset of cramps linked to heavy sweating and sodium loss, but they're not a cure-all, and the science says they won't prevent fatigue-driven cramps on their own. That said, there's a real category where they matter: the salty sweater grinding through a hot Durban or Joburg long run, losing serious sodium over several hours. For that runner, replacing sodium genuinely supports muscle function and overall hydration, even if it isn't the whole story.

So treat electrolytes as one tool, not the answer. Steady hydration with sodium across a long, sweaty run is worth doing, and for runners with a stubborn history of cramping we add a dedicated product. We reach for 32Gi Cramp Assalt, taking one about 30 minutes before the start and then one every couple of hours through a long race. Pair that with a sodium-carrying drink like 32Gi Hydrate rather than plain water, and you've covered the hydration side properly while your training handles the fatigue side.

What Should You Do When a Cramp Strikes Mid-Run?

When a cramp hits, stop and gently stretch and hold the affected muscle, because a slow static stretch calms the over-excited nerve signals driving the spasm. For a calf cramp, straighten the leg and pull your toes up toward your shin. For a hamstring, straighten the leg and lean gently forward. Hold it, breathe, and let the muscle release rather than fighting it.

Once it eases, ease back in. Walk first, then jog gently, and drop your pace for a while rather than charging straight back to race effort, which often just retriggers the cramp. If your legs are clearly cooked, accept that finishing slower beats not finishing at all. A cramp at 30km is your body flagging fatigue, so the smart move is to manage the rest of the run, not to bully through it.

Why Do You Cramp More in Hot South African Conditions?

You cramp more in the heat because hot conditions push your sweat and sodium losses higher and make you fatigue faster, stacking both cramp triggers at once. A summer long run in Joburg or a humid coastal morning raises your sweat rate, drains more sodium, and tires your muscles quicker than a cool-weather run at the same pace. That combination is why cramps spike on warm race days.

The answer is to manage both sides on hot days. Start well hydrated, carry sodium rather than plain water, and pace more conservatively than you would in cool weather because the heat is already taxing your legs. We hand-select every race-day product we stock because we've cramped our way through enough Comrades and Two Oceans builds to know what helps. For the full race-day picture, our Comrades Marathon nutrition plan maps out hydration and fuelling, and you can browse our competition day range to sort your kit before race week.