Muscle cramps: overview and causes

Partager l'article

What is a cramp?

A cramp is a painful, temporary, involuntary contraction of a muscle. It is visible. It affects all or part of a single muscle or a group of muscles that work together (e.g., the calf or finger flexor muscles).

No matter when it happens—during a workout, while resting during the day, or even in the middle of the night—sudden pain strikes your calf, foot, leg, arms, or hands. There's no doubt about it: it's a cramp.

Cramps often occur during exercise, but can also strike when you are resting. The good news is that they are not serious and do not leave any lasting effects. They are nothing like a muscle strain or tear, which require a real recovery period.

How does a cramp occur?

Cramps only affect muscles.. These muscles that, when contracted, enable the joints to move. They are connected to the bones by tendons, and their structure is composed of bundles made up of muscle fibers.

Looking more closely, inside muscle fibers, we find actin and myosin filaments, as well as motor nerves responsible for activating them to produce movement. These nerves obey commands from the brain most of the time. When a muscle contracts, these filaments slide over each other, shortening the muscle by 20 to 50%. The muscle then relaxes and returns to its normal length. But when the contraction is too sudden or uncontrolled... that's when a cramp can occur!

Thus, a cramp can occur whenever there is a sudden or uncontrolled contraction of the muscle, regardless of the reason. The mechanism of a cramp is simple and does not cause any muscle damage. However, its causes are often complex to identify and can vary from person to person.

Causes of cramps

Cramps remain largely unexplained to this day.

Since the late 1980s, neurophysiological research has confirmed that muscle cramps result from sudden hyperactivity of the motor nerves. However, this does not explain everything: cramps are a complex phenomenon that also involves metabolic mechanisms. Furthermore, it is rare for a person to be studied as a whole, which complicates the precise understanding of the origin of their cramps.

For example, a leg cramp does not necessarily occur after athletic exercices or activities that strain the lower limbs. It may simply be due to blood imbalance (in its composition or texture in the event of dehydration).

It is because of this complexity in diagnosis that the reason for their appearance is not always found. The causes can be numerous and multifactorial.

Muscle fibers require ions, including potassium, sodium and calcium. It is the exchange of these ions that allows the muscle to contract or relax.

  1. Sodium and calcium

When sodium levels outside the cells decrease, particularly due to water loss through sweating during training or competition, calcium/sodium exchanges at the cellular level become disrupted. This causes calcium to accumulate inside the cells. However, intracellular calcium concentration is crucial for muscle contraction. This excessive accumulation then leads to involuntary and prolonged muscle contraction, causing cramps.

2. Magnesium

An acute magnesium deficiency can also cause cramps. This mineral plays a key role in the “communication” between muscle and nerve cells, as well as in muscle relaxation after contraction. When magnesium is lacking, muscles can tense up uncontrollably.

3. Potassium

Potassium is an electrolyte, a mineral that is electrically charged when dissolved in bodily fluids such as blood. It is essential for the proper functioning of cells, muscles, and nerves.

Low potassium levels can have several causes and can lead to weakness, cramps, muscle spasms or even paralysis, and heart rhythm abnormalities.

When muscle fibers lack oxygen, they produce too much oflactic acid. The effort becomes more difficult, the release of calcium ions is disrupted, and the muscle can no longer relax—that's when a cramp occurs!

Some recent studies point to a nervous cause linked to motor neurons located in the Golgi tendon organ—a nervous structure found wherever muscle fibers attach to tendons. When this organ can no longer perform its role of regulating electrical activity, the muscle becomes overexcited beyond the threshold, causing a cramp.

For athletes, in order to compensate for water loss generated by physical activity (remember, 80% of the energy produced is released in the form of heat and therefore sweat), it is necessary to drink, in addition to the 1.5 liters recommended for sedentary individuals, approximately 500 to 700 ml per half hour of physical activity (and even more in hot weather).

Know that:

  1. Some people sweat a lot and need to pay special attention to their fluid intake, and even their electrolyte intake.
  2. Sweating also occurs in water sports, mainly swimming, even though it goes unnoticed because the body is submerged. Drinking during swimming is essential, especially if it is prolonged and intense.

The day before a cramp occurs, muscles may have been overworked or used in a different way than usual. When you change your habits, your muscles are no longer prepared for the effort required and have difficulty relaxing, which increases the risk of cramps.

For example, if you have a competition in a new city, avoid visiting it the day before the race. Walking and standing around can tire your muscles and trigger cramps during the event. It is better to save your sightseeing for after the race.

Alcohol, tea and coffee are diuretics and cause dehydration. When consuming these beverages, it is recommended to drink twice the volume of water as the amount of alcohol or tea consumed to avoid cellular dehydration.

Avoid excesses! And remember that water remains the only essential and necessary source of hydration.

Some medications can have side effects that promote cramps. It is therefore important to always read the package insert carefully and consult your doctor if you are taking a new or unfamiliar medication.

Heat waves can cause dehydration which will alter intracellular and extracellular balances and ion levels and their circulation in the body.

Not only one answer

There is no single cause for cramps, and the factors mentioned here do not cover everything. It is by considering the individual as a whole—age, fitness, diet, hydration, medical treatments, history, changes in habits, environmental factors, etc.—that we can hope to identify the possible reasons for cramps.