Ever been suddenly brought to a halt mid-workout with the severe pain of muscle cramps? Then you’ll know how frustrating they can be. Some people are prone to developing cramps, and certain conditions (such as the hot and humid Hong Kong summers) make them more likely, too. Find out here about the latest thinking on causes of muscle cramps and what you can do about them.

What are exercise-induced muscle cramps?

Cramp is a painful, involuntary contraction of a muscle group, a single muscle or part of a muscle. Exercise-induced cramps happen most commonly in the muscles of the calf, the back of the thigh or the foot. However, they can happen anywhere.

Despite being quite common, scientists still don’t fully understand why this exertional cramping occurs.

It’s clear that greater intensity and duration of exercise is more likely to produce cramping. But there are several theories about the underlying cause.

The involuntary contraction happens because of aberrant electrical signals causing overstimulation of the muscle fibres. So what produces this faulty signalling?

Electrolyte imbalance and dehydration

The body can lose an amazing two litres of fluid per hour in sweat during intense exercise. And it’s not just water we lose in sweat, but minerals such as calcium, potassium and sodium too.

These minerals (or ‘electrolytes’) exist in blood plasma and in the fluid between and inside cells. They have an important role in normal muscle function. They exist as electrically charged ions, and their flow in and out of muscle cells triggers the contraction and relaxation of the muscle.

Dehydration plays a part because loss of body fluid changes the concentration levels of the electrolytes. The body needs to maintain these levels in tightly controlled ranges for proper function.

It seems reasonable, then, that any significant tip in this carefully controlled electrolyte balance could trigger uncontrolled muscular contractions.

And, indeed, there is evidence that replacing lost electrolytes is a good way to reduce cramps. One study compared the ease with which cramps could be induced in runners. Some rehydrated with plain water, and some with an electrolyte drink. They found that plain water increased the potential for cramp, whereas the electrolyte drink reduced it. This might be due to the plain water further diluting the already-diminished electrolytes in the body fluid.

Altered neuromuscular control

However, the electrolyte theory can’t be the whole explanation. If electrolyte loss is body-wide, why do only some muscles develop cramp? And how do we explain cramps that happen to people who are not dehydrated?

More recent research has come up with an alternative idea. One study compared electrolyte levels in Ironman athletes who experienced cramps with those that did not, and it found no difference between them. However, it was measuring electrolyte levels in the blood, which may not be a good indicator of that in the fluid in and around the muscle cells.

Scientists have therefore proposed an idea that muscle fatigue is the underlying factor that triggers exercise-induced muscle cramps. This fatigue, likely during strenuous and prolonged exercise, appears to affect the central control of the muscle through the nervous system.

Normally, the brain receives feedback from specialised nerve endings in the muscle and its tendons. This gives the brain information about how to balance contraction and relaxation of the muscle. Scientists conjecture that overexertion of a muscle can alter this normal nerve reflex, allowing unchecked contraction to occur.

The effect of heat

It has long been recognised that overheating makes people more vulnerable to cramps. These cramps seem more sustained and intense than cramps that are induced by fatigue alone.

Of course, people sweat in hot conditions. We know excessive sweating leads to dehydration and electrolyte loss – in particular, sodium loss appears to be significant. Even the study on Ironman athletes, which concluded that cramp was related to fatigue rather than electrolyte imbalance, found that athletes with cramp had a drop in sodium immediately after the race.

And research related to the workplace, rather than to sports, has repeatedly shown the link between cramps and heat. A recent one-year study looked at heat exhaustion in Australian mine workers. It concluded that cramp was so pervasive that it should be considered a symptom of heat exhaustion, and that dehydration was a major factor.

Muscle cramps – a complex condition

Despite this shift away from hydration and electrolyte balance as a complete explanation for muscle cramps, there are good reasons not to ignore it.

A single cause for all exertional muscle cramps appears unlikely. Instead, different factors play a greater or lesser role depending on individual circumstances.

It seems plausible that the two effects interact. Electrolyte and fluid imbalance is body-wide, and a muscle fatigues within this environment. Perhaps this makes muscles that become overexerted more vulnerable to developing cramp. This may explain why electrolyte replacement can still be effective, even if fatigue is the main trigger.

And there’s no denying that good hydration is vital to athletic performance. Loss of fluid causes a drop in blood volume. The heart must work harder to accommodate the metabolic needs of the working muscles, risking their early fatigue, and therefore cramp.

Top tips for dealing with muscle cramps

It looks like exercise-related muscle cramps are complicated and depend on your individual circumstances. As such, there’s no one-size-fits-all solution. But there are several things you can try to help keep the cramps at bay:

• If you’re aiming to increase the intensity or duration of your exercise, do it in incremental steps to allow your muscles to adapt to the new demands.
• Always warm up and cool down with a range of dynamic stretches targeting any cramp-prone muscles.
• If you experience a bout of cramps, a gentle stretch can ease the spasm.
• Hydrate well in the day or two before a workout or race, so that you already have some fluid reserves.
• Use a drink containing electrolytes and carbohydrates during a workout longer than an hour. Sip it little and often to maintain the right levels.
• Avoid overheating. Cool down with damp towels or a post-workout shower. Keep your sleeping environment cool to reduce the risk of night-time cramps.
• Some evidence suggests that supplementing with creatine can reduce the occurrence of muscle cramps.
• Replace lost electrolytes after a workout through food intake, or use a product designed for the purpose (we recommend Bix rehydration products, which are complete and additive-free). This will help you take on fluid without diluting the electrolytes in your system.

In summary, there’s a shifting body of science trying to explain how and why strenuous exercise can trigger muscle cramps. More research is needed to fully understand the various causes, and how they interact. But, at OCHK, we love nothing more than keeping abreast of the latest thinking and applying it in the way we manage and advise our clients. So, don’t let muscle cramps put you off enjoying your favourite sport – even in Hong Kong’s humid summer!

And if you’re preparing for an event, why not let our team of osteopaths and corrective exercise specialists help prepare you with sports-specific strength training and injury prevention? Book in today.