What causes muscle cramps during exercise?

One of the most common myths in exercise science is that muscle cramps during exercise are caused by dehydration and/or electrolyte depletion. Don’t get me wrong, these two factors can cause muscle cramps (think severe vomiting etc. when you have a stomach bug), but research has found that these are mostly not to blame for the cramps we get during or after exercise. Buskard (2014) recently published an article in the Strength and Conditioning Journal in which he reviewed all the available research on this topic.

Muscle cramp causes: What we used to think

Factors that we traditionally blamed for muscle cramps during exercise include:

• Accumulation of waste products that interfere with the muscle contraction

• Electrolyte depletion (loss of salts or electrolytes)

• Loss of fluid volume (dehydration)

• Extreme environmental conditions e.g. extreme heat or cold

The research has, however, shown that most of the above factors are likely NOT the cause of muscle cramps in healthy individuals. There's an easy way to test to see if you're dehydrated so if you don't quite believe me check out this article.

Two large studies that tested athletes after an Ironman triathlon and an ultra-marathon found no difference in hydration status or blood electrolyte levels between athletes who cramped up and those who did not.

Heat and cold also do not induce cramps in muscles, but researchers do agree that the extreme weather conditions may lead to greater fatigue, which is currently seen as the main cause for cramping.

What we currently think causes muscle cramps during exercise

Muscle fatigue is the one factor that nearly all studies in this area has identified as a cause for exercise induced muscle cramps. The exact mechanism involved in this process is however still unclear.

The altered neuromuscular control theory is the one that currently has the most scientific evidence in support of it. ‘Neuromuscular control’ can be defined as ‘how the nervous system (brain, spinal cord, nerves) controls the muscle’. This theory is based on the belief that fatigue causes changes in the firing patterns of the nervous system which in turn leads to muscle cramps.

A muscle’s tone (how tense or relaxed it is) is controlled via the spinal reflex, where a receptor in the muscle sends a message to the spinal cord which in turn triggers a message to be sent back to the muscle. There are receptors in the muscle itself that can either increase the nerve’s activity (muscle spindles) via the spinal reflex and thus increase the muscle tone/contraction or decrease the nerve’s activity (Golgi tendon organs) and thus decrease the muscle tone/contraction when stimulated. These receptors have the ability to influence each other’s output e.g. increased firing of the Golgi tendon organs will lead to a decrease in the muscle spindle activity and cause the muscle tone to decrease (muscle relaxes).

What the researchers are suggesting is that muscle fatigue causes the neural control of these receptors to become unbalanced so that the muscle spindles’ activity increases and causes a strong unregulated contraction.

Researches view the fact that stretching a muscle helps to alleviate cramps as support for this hypothesis. When you stretch a muscle, you activate the Golgi tendon organs, which in turn decrease the muscle spindle activity. This hypothesis is further supported by the findings that cramps more frequently occur in shortened muscles and in ones that cross 2 joints since the Golgi tendon organs will be less active under these conditions.

The research currently suggest that the following factors appear to predispose a person to exercise induced cramps:

• Having a history of cramping

• Individuals who cramp regularly have been shown to have a lower threshold frequency for cramps. This means that, during testing, it took less electricity to annoy the nerve and cause a muscle cramp in people who often cramp vs. ones that don’t. (Who volunteers for these studies?!) This may point to a genetic predisposition to cramping.

• Competing at a faster race pace than training pace (putting in a greater effort = greater fatigue).

• It was also suggested, but not yet investigated, that sub-clinical muscle damage due to insufficient tapering can cause cramp during a race.

What can you do to prevent muscle cramps while exercising?

• Race nutrition. A group of researchers found that using a sports drink consisting of a mixture of carbohydrates, electrolytes and water significantly delayed the onset of muscle cramps during exercise. Their participants still experienced muscle cramps while drinking this mixture, but it allowed them to exercise for about 150% longer before cramping up. This study can unfortunately not tell us which of these 3 ingredients worked the magic, but my guess would be that the water and carbohydrates were the most important. It has previously been shown that adequate water and carbohydrate intake during exercise can prolong the onset of fatigue. Your body should have enough electrolytes unless you are following a very restricted diet.

• Train at race pace. Make sure that you complete some of your training at race pace. This will limit fatigue on race day.

• Dress appropriately. Overheating can lead to increased fatigue which may increase your chances of cramping.

• Taper your training in time to allow your muscles to recover. Racing on tired muscles will once again lead to early fatigue.

What to do if you cramp up during exercise

• Stretch. Hold the stretch for a loooong time. As explained above, this will activate the Golgi tendon organs and relax the muscle.

• Slow down and walk or free wheel if cycling. This will give the muscle time to recover.

Need more help with your injury? You’re welcome to consult one of the team at SIP online via video call for an assessment of your injury and a tailored treatment plan.

About the Author

Maryke Louw is a chartered physiotherapist with more than 15 years' experience and a Masters Degree in Sports Injury Management. Follow her on LinkedIn, ResearchGate.

References:

1. Buskard, A. N. L. (2014). Cramping in Sports: Beyond Dehydration. Strength & Conditioning Journal, 36(5), 44-52