Demystifying science | The mystery of cramps and side stitches

Every week, our journalist answers scientific questions from readers.

There is uncertainty about the cause of these two ailments afflicting athletes.

“Calf cramps are thought to have a nervous origin, but their cause is not identified with certainty,” explains Gaia Giurato, a neurophysiologist at the University of Verona, Italy, who took stock of the issue in 2018 in the Journal of Electromyography and Kinesiology. “There are few studies on the issue, because it is not a problem that can put a person’s life in danger. »

The two hypotheses to explain cramps are nervous hypersensitivity and poor functioning of the reflex which manages muscle tension.

“At first, we thought it was due to dehydration or heat, because it often occurs among miners and it is hot in the mines,” says the researcher. For example, athletes were recommended to eat a banana before doing sports to get calcium, which is lacking when you are dehydrated. But these two causes were ruled out a few decades ago, and we concluded that it was a nervous problem. »

The nerves in question control muscle tension. If they are too sensitive, or if they do not respond to the reflex to stop muscle tension after a certain time, the muscle remains in a tense position, which becomes painful over time.

“I think it’s more a reflex problem,” says M.^me Giurato. One of the known ways to relieve a cramp is to massage the calf. This can promote the transmission of the reflex signal through the tendons. »

Two other aspects of cramps, their higher frequency during pregnancy and nighttime cramps, are even more mysterious and less well studied.

Due to the lack of medical interest in this problem, it is difficult to find funding. Gaia Giurato had a research project to determine which of two possible causes of cramps was the correct one, but she was unable to fund it.

She became interested in this question because before graduate school, she competed in long jump and regularly suffered from cramps. “I didn’t understand why I had these cramps. I decided to study them. » She is now a specialist in the physiological differences between men and women, particularly at the level of the mitochondria, the energy factory of human cells.

How can you prevent cramps? “We have talked about stretching, but their effectiveness in preventing cramps has never been demonstrated. Some believe that dehydration can worsen the reflex problem or that muscle fatigue can create an imbalance of adenosine triphosphate. [ou ATP, une molécule impliquée dans le transfert de l’énergie entre les cellules]. But what clinical implication this has for prevention is not clear. »

Side stitches

Research on side stitches, whose technical name is exercise-related transient abdominal pain (ETAP), is limited for the same reason: because no one is going to die from it, it’s difficult to get funding to study its causes.

Australian researchers are the only ones to have looked into the question assiduously at the start of the millennium. In a study published in 2015 in the journal Sports MedicineDarren Morton and Robin Callister of Avondale University, in Cooranbong north of Sydney, list a long list of possible causes.

They include a lack of oxygen to the cells of the diaphragm or gastrointestinal organs, damaged ligaments in the diaphragm, gastrointestinal distension, abdominal cramps, compression of arteries, hypersensitivity of the spinal nerves and irritation of the peritoneum. Contacted in Australia, Darren Morton today believes that this last explanation is the most likely.

The study by physiologists from Avondale University is one of the few to have looked at the frequency of ETAP. Swimming and running are the sports where it is most common, with a quarter of these athletes experiencing it during a given sporting event. More than two thirds of runners and swimmers had already had side points during their career, according to this survey conducted in 2000 among 965 athletes. Cyclists are the least likely to have side stitches, with less than a third having ever suffered them.

To prevent side stitches, Australian physiologists suggest avoiding eating or drinking two hours before exercise, straightening your posture and improving your abdominal muscles, or even supporting the abdomen with a postural belt. But they note that none of these prevention methods have been tested experimentally.