Most of us at some stage of our life have probably experienced the intense pain of a muscular cramp. This sudden and debilitating condition occurs when a muscle goes into “lock down”, or literally a powerful, involuntary and unrelenting contraction.

Male athlete on floor clutching knee and hamstring in excrutiating pain on white background

Cramps can theoretically affect any one of your 650 skeletal muscles, however the most common muscle groups involved are:

Back of lower leg/calf (gastrocnemius)

Back of thigh (hamstrings)

Front of thigh (quadriceps)

Sole of the foot (particularly when using the Pilates reformer!).

So why do cramps occur, and what can we do to not only manage a cramping muscle, but to prevent cramps from happening again? Read on to help answer some of the questions, and dispel some of the myths about cramps.

What Causes Cramps?

Just about everyone will experience a muscle cramp sometime in life, but those at greatest risk for cramps and other ailments related to excess heat include infants and young children, people over age 65, and those who are ill, overweight, overexert during work or exercise, or take drugs or certain medications. The exact cause of cramps is unknown, however listed below are some of the theories of why cramps may occur:

Muscle fatigue and deconditioning:

This is probably the most common reason for cramping in athletes, who are more likely to get cramps in the preseason when the body is not conditioned and therefore more subject to fatigue. Likewise cramps are very common when someone is beginning an exercise program, or pushing themselves to new limits. In most cases, muscles are being pushed beyond their level of conditioning, and quite simply, the muscle cannot tolerate any more load or movement. A cramp is like the muscles way of saying “enough is enough”! These cramps often develop near the end of intense or prolonged exercise, but can develop some hours after exercise also.

It is extremely common to see cramping of a severe nature towards the latter stages of marathon running, even in highly conditioned athletes. Is it lack of fitness (not likely in highly trained athletes), heat (cramping still occurs in colder temperature marathons), electrolyte imbalance through sweating (poorly supported by evidence as you will see below)? In a great study performed at the 2009 Manchester City Marathon, it was demonstrated how significantly running form and biomechanics changed from the 10km mark to the 32 km mark (and there was still 10km to go) – things like heavier heel strike, less forefoot strike, gluteal fatigue, slouched posture, and less hip extension all happen in a fatigued athlete, and the calf is one area that cops a lot of the brunt of this change in biomechanics, requiring the calf muscle group to compensate and bear considerably more load.

It is very likely that this change in posture and biomechanics is one of the greatest causes of general cramping during exercise.

Heat & Dehydration

Muscle cramps are more likely when you exercise in hot weather because sweat drains your body’s fluids, causing loss of salt and minerals (i.e., sodium, potassium, magnesium and calcium). Loss of these nutrients can cause a muscle to spasm.

Many people underestimate the magnitude of their fluid loss. Even in sports like swimming, we sweat a lot and lose electrolytes! It is very difficult to avoid dehydration during a long race, particularly in warm weather, because the rate of sweat loss usually exceeds the rate of absorption of ingested fluids. Our gut, or gastro-intestinal tract, has a maximum rate of absorption of fluid. This means that we can only absorb a certain amount of fluid in a particular time – regardless of how much fluid we ingest (this explains why you need to go to the toilet when you have drunk a lot of water – you may have ingested 500ml of water in 10 minutes, but the gut may only be able to absorb 80 ml of that. The other 420ml ends up in the bladder).

The actual absorption rate of the gut is around a maximum of 800 ml per hour, whereas the rate of fluid loss through sweating may average as high as 1.5 – 2 litres per hour. Thus often, despite the best fluid intake, dehydration will occur. Drinking 150 – 250 ml every 10 – 15 minutes is probably the best way to attempt to stay hydrated during exercise. For any stressful or endurance activity you must determine and plan you hydration strategy ahead of time.

There is poor evidence that heat alone causes cramps however. Even swimmers in cold water can cramp!

Electrolyte Depletion

As mentioned above, sweating causes electrolyte depletion, but so do many other causes. Illness (fever/sweats, and especially the combination of vomiting and not eating/drinking), poor diet, and poor daily fluid intake are all predisposing factors for cramping during exercise. Some of the important electrolytes we lose in exercise and sweating are:

SODIUM:The body needs sodium to help maintain normal fluid balance and blood pressure in the body, and it is also critical for nerve impulse generation and muscle contraction. This is where some salt in your diet, and the use of electrolyte drinks like Gatorade etc may help. A small study completed in 2005 directly tested the effect of salty sports drinks on exercise performance, and found that whilst the use of electrolyte drinks did help participants exercise a bit longer before cramp set in, most still developed cramping!

POTASSIUM:is the major electrolyte found inside all body cells, including muscle and nerve cells. Like Sodium, it is critical in the generation of electrical impulses in nerves and muscles, including the heart. Potassium is found in most foods, but is especially abundant in fresh vegetables, potatoes, certain fruits (melon, bananas, berries, citrus fruit), milk, meat, and fish. Interestingly, there appears little evidence to link low potassium intake and muscle cramps, however the banana is still the first line of defence in many athletes mind to help prevent muscle cramps. If only it were that simple!

CALCIUM:Calcium, as well as helping bone strength, is also involved in muscle contractions and the generation of nerve impulses. Impaired muscle contraction and muscle cramps are commonly listed as symptoms of calcium deficiency, however as with Potassium, there isn’t a lot of conclusive evidence to link calcium depletion with cramps.

Despite this, calcium is one of the nutritional factors people most associate with relieving cramps, second only to the potassium-rich banana.

MAGNESIUM:Magnesium plays an important role in muscle contraction, and also serves as an electrolyte in body fluids. Muscle weakness, muscle twitching, and muscle cramps are common symptoms of magnesium deficiency. There is some data to suggest that magnesium levels are indirectly related to the incidence of muscle cramps. Anecdotally we tend to hear of more people responding well to Magnesium supplements than other supplements.


Unfortunately along with all the other deteriorations we feel as we age, older people are more susceptible to muscle cramps due to normal muscle loss (atrophy) that begins in the mid-40s and accelerates with inactivity. As you age, your muscles cannot work as hard or as quickly as they used to (but often our minds tell us we are still 20 years younger!). The body also loses some of its sense of thirst and its ability to sense and respond to changes in temperature, making cramps more likely. Maintaining muscle strength through resistance exercise is important as we age.

How Does A Cramp Occur?

The Neuro-Muscular Theory

Normally, nerves in the tendons of muscles send information back to the spine about the state of the muscle and tendon. Once a muscle is fatigued, oxygen supplies are depleted, and biomechanical changes occur causing less efficient movement patterns, leading to a build-up of lactic acid and waste products. This build up alters the activity of the nerves, causing over stimulation of these nerves, and a reflex reaction from the spinal cord which stimulates the muscle to keep contracting, resulting in a cramp.

Regardless of the cause of a cramp, the cramping itself appears to be the result of the failure of some type of cramp-inhibiting reflex in the spinal column. In normal situations a reflex reaction of the spine will help inhibit over-firing of that muscle.

nterestingly, stretching sends a strong inhibitory message to the spine and aids this cramp inhibiting reflex reaction, which helps explain why stretching the affected muscle helps so much.

Why does Quinine Work?

Ever heard that drinking Tonic water is good for muscular cramps? Tonic water contains quinine, a substance that has been shown to decrease the excitability of nerves that supply messages to muscles, therefore reducing the contractile ability of the muscle. It has been found anecdotally to really help cramps, and has even been given in tablet form in some cases. Quinine does have some serious potential side effects in higher doses, but having a glass or two of tonic water might be worth a try if you suffer night time cramps.

Finally, it is important to note that whilst most muscle cramps are benign, sometimes they can indicate a serious medical condition. See your doctor if cramps are severe, happen frequently, respond poorly to simple treatments, or are not related to obvious causes like strenuous exercise. You could have problems with circulation, nerves, metabolism, hormones, medications, or nutrition.

In summary, there are quite a few thoughts, and many myths, surrounding the cause behind muscle cramping in athletes. Basically, we don’t really know because there doesn’t seem to be strong evidence to support any one theory. What does seem reasonable to say is that overload and fatigue are certainly critical, so ensuring you train well, are conditioned for the activity you are performing, and maintain technique as much as possible when you get tired, are probably the main factors you should be directing your atte