Fatigue a prime factor in muscle cramps

There are a variety of muscle cramps, but I will primarily be discussing those that occur during or after exercise.

Fatigue a prime factor in muscle cramps

Many of us at one time or another have experienced a muscle cramp – a sudden, involuntary, usually painful muscle contraction accompanied by nerve firing which is relieved usually by stretching and resting the muscle for a few minutes.

Some cramps can recur for hours during the day. There are a variety of muscle cramps, but I will primarily be discussing those that occur during or after exercise.

The incidence of exercise-related muscle cramps is around 30-50 per cent in the general population and can be as high as 95 per cent of an active, exercising population for at least one occurrence of cramping.

Since these muscle cramps often occur with profuse sweating and sometimes in hot conditions, the cause for decades was thought to be related to dehydration or electrolyte depletion or balance. This is probably because of the role of water and electrolyte balance in muscle function and that cramping usually occurs with profuse sweating. Mechanisms were proposed for the role of lactic acid, sodium, potassium and others. This then led to a wide and sometimes colourful array of cures for cramping, including eating bananas or drinking pickle juice, among others.

However, when scientific research has been done, hydration and electrolyte loss are not the culprits. A number of recent studies have been done at long distance races, such as Ironman triathlons and ultra-endurance marathons. In these studies, the athletes who experienced cramping during or after the race were evaluated for dehydration and electrolyte composition. Those with cramping had no significant difference in hydration or electrolyte levels compared to those athletes in the race that had no cramping. However, one factor was common to the cramping groups, and that was that their race pace was significantly faster than their training pace, or they raced further or longer than they had trained for. This indicates that fatigue, or pushing the muscle beyond its training limits may be prime factors in triggering muscle cramps. Researchers also noted that athletes who had cramping during the races also had a history of muscle cramps.

Studies over the last decade have increasingly led researchers to conclude that muscle cramping is related to nervous system malfunctioning. There is still some debate about whether the peripheral or central nervous system is the trigger, though the central nervous system currently seems to have the balance of the evidence.

Each muscle has feedback loops via the nervous system to protect the muscle from injury. One of these loops consists of stretch detectors inside the muscle fibres called muscle spindles. When these spindles detect stretch in the muscle, they send a message to the spinal cord, which in turn sends a message to the muscles to contract so they don’t get pulled apart or torn.

On a separate feedback loop, each tendon contains another sensor called the Golgi Tendon Organ. When the GTO gets stretched under sufficient load, it sends a message to the muscle, telling it to relax, again presumably to prevent overload and damage. When enough fatigue occurs in the muscle, sometimes the spindles become overactive, creating a positive feedback loop and contract the muscle involuntarily and continuously giving the athlete painful contraction we know as cramping. The normal relaxation mechanism does not occur and so the athlete must try to gently stretch the muscle themselves, activating the GTOs, thereby sending relaxation messages and normalizing muscle function.

It is interesting to note that cramping most often occurs in muscles that are already short or in muscles that cross two joints, such as the calf, the quadriceps or the hamstring group.

To date, there is no known sure-fire prevention for muscle cramping, though athletes are well-advised to maintain optimal levels of flexibility (especially of two joint muscles), and taking care not to compete at levels much beyond training levels.

And if cramping does occur, performing passive stretching will help alleviate the cramp.


– Kerry Senchyna holds a bachelor of science degree in kinesiology and is owner of

West Coast Kinesiology in Maple Ridge.