During this year’s World Cup, one scene repeats itself game after game: Several players take the field with holes in the calves of their socks. Social media is rife with theories about the supposed competitive advantage this might give them. But the practice isn’t new. It has been seen at the European Championships, the Olympic Games, and other international competitions over the past decade. Still, science has yet to find evidence that it improves performance.

Professional soccer socks are, by design, form-fitting. In addition to holding shin guards in place, they provide support to the ankle, the arch of the foot, and the calf; they help manage moisture and reduce foot movement inside the cleat to improve stability. This design principle has been used in professional soccer for decades. Although materials have evolved to become lighter and more durable, they are still primarily based on synthetic fibers such as polyester, nylon, and spandex.

But quite a few players have complained that the socks are too tight and cause a tingling and numb sensation in the calf area. The discomfort is so great that, halfway through a game, they cut several holes in the calf area to “release tension” and run better.

There is a biomechanical component to this sensation. During a sprint or a change of direction, the largest muscle in the calf contracts and increases in thickness to generate the force that propels the athlete forward. This change in shape occurs thousands of times during a game. For some, the repeated expansion of the muscle is enough to create a sensation of pressure when the sock exerts constant compression on the calf.

Over time, the practice of cutting holes in socks has taken on an almost intuitive explanation among the players themselves: splitting open the fabric allows the muscle to “breathe,” relieving pressure and reducing the likelihood of pain or cramps. However, specialists in sports medicine and recovery point out that there are no studies demonstrating that cutting holes in socks provides any benefit. In fact, much of the research on compression garments concludes that, when properly designed and fitted, they can help limit muscle inflammation after intense exertion.

Despite the lack of evidence regarding physiological benefits, the practice continues to spread among professional soccer players. Today, it is considered primarily an anecdotal phenomenon, based on each player’s personal experience rather than scientific evidence. Furthermore, the rules of the game do not prohibit modifying socks, as long as the equipment remains safe and the shin guards remain properly covered. (A soccer player, however, cannot play with a torn jersey.)

Given the lack of scientific evidence, several specialists believe that part of the phenomenon could be explained by the player’s own perception of comfort. In high-performance sports, the feeling of comfort can influence the confidence with which an athlete competes. If a soccer player believes a piece of clothing is restrictive, eliminating that perceived discomfort can make them feel freer to run, accelerate, or change direction—even if their performance remains objectively unchanged.

Though there is no evidence that cutting the socks provides a competitive advantage or reduces the risk of injury, that does not mean the sensation of discomfort is imaginary. The perception of pressure, restriction, or comfort depends on multiple factors, ranging from anatomy and individual sensitivity to the athlete’s past experiences. In other words, two players may react differently while wearing exactly the same equipment.

For now, it seems the cutting of socks will continue. The available evidence points to a mechanism similar to that of other sports rituals: Its effect is primarily psychological, not necessarily physiological.

This article originally appeared on WIRED en Español and has been translated from Spanish.