Foto: iStock.com/olegbreslavtsev

Who doesn’t know this? The marathon is going really well and you're on your way to achieving a new best time when they suddenly strike at the 35-km mark: darned muscle cramps!

Why do you get cramps?

The sudden, unwanted, and painful contraction of all or part of a muscle can generally be caused by metabolic disorders or diseases at the level of the nerves. However, cramps can also occur in healthy people with no such disorders. These also include the classic cramps during sports. 

Attributing cramps during sports activities to heavy sweating and subsequent dehydration with or without major mineral (electrolyte) losses as well as changes in the mineral content of blood during exercise is a topic that is under continuous debate. However, cramps are more likely to be caused by an imbalance in the signal transmission between nerves and muscles. Nevertheless, the exact mechanism of exercise-associated cramps is not yet fully understood. 

The following aspects are currently being discussed as potential factors that increase the risk of muscle cramps during sports: higher (than usual) load intensity, number of cramps already suffered, training in a humid and hot environment, fatigue. Moreover, men seem to be more susceptible to cramps than women. It is assumed that various triggers contribute to the occurrence of cramps, not just a single cause.  

What about magnesium?

The scientific literature on magnesium and cramps is generally very sparse. But according to the most recent summary of all properly conducted studies, the magnesium supplements taken by adults who suffer cramps of any kind do not significantly prevent cramps. As mentioned above, there are no properly conducted studies of exercise-associated cramps. The blanket promise that magnesium will help with cramps during sports cannot therefore be supported from a specialist point of view. And the use of magnesium supplements to treat leg cramps during pregnancy is no more effective than a placebo or doing nothing at all. 

Magnesium is involved in hundreds of metabolic reactions, including the provision of energy. In the case of a magnesium deficiency, in addition to the occurrence of muscle cramps, almost the entire metabolism would crash… Since muscle cramps during sports obviously do not coincide with a completely derailed metabolism, the assumption of a causal relationship between magnesium deficiency and cramps is already difficult to sustain on a theoretical level.

Sometimes magnesium is also taken directly before a performance. However, the available data cannot support this use in sports either.

Too much magnesium at once

While it is virtually impossible to absorb too much magnesium from natural, non-fortified foods, this can happen quite easily if supplements are taken on a regular basis. Accordingly, the side effects of too much magnesium have so far only been described for supplements.

The so-called tolerable upper intake level for magnesium via supplements (and fortified foods) – or the intake that must not be exceeded in the long term – is only 250 mg per day. Too much magnesium via supplements or fortified foods increases the risk of diarrhoea. In addition, it can inhibit the absorption of iron or zinc.

What can be done against cramps?

Looking the possible causes of cramps during sports identifies the measures needed to avoid them. Even if not particularly spectacular, the relevant measures should involve good training practices, including ideal training or competition preparation. This includes sufficient recovery, especially after hard training units, as well as a sensible diet during the training/competition along with an adequate fluid intake. As soon as you get close to or even exceed your physical limit, the risk of cramps increases. Stretching seems to be the most effective method for the acute treatment of cramps.

Conclusion

Magnesium should ideally be ingested through your normal diet and not as a supplement. This ensures you will hardly ever consume too much magnesium. And with a reasonably varied food selection, if you don't have a (metabolic) disease, you won't have to worry about a magnesium deficiency.