How biochemistry fuels World Cup athletes

In the FIFA World Cup, tactics and skills certainly matter, but none of the competition’s glorious goals and heartbreaking defeats can happen without carbohydrates and electrolytes. Athletes from around the world have been preparing so they can compete in this year’s 39-day edition of the quadrennial world soccer tournament in top condition. Peak performance isn’t just about practice, though. It’s also about fine-tuning the biochemistry that fuels players’ bodies throughout the competition.

Biochemists and other experts say that smart competitors—and the nutrition experts who support their teams—will be paying close attention to sugars, salt, and sweat.

To make their muscles contract, athletes need adenosine triphosphate, also known as ATP. The body has three main options for making ATP, says James Morton, a professor of exercise metabolism at Liverpool John Moores University who was head of nutrition for the Liverpool Football Club for 5 years.

At rest or during low-intensity exercise, the body makes ATP by using oxygen to oxidize fats and carbohydrates, which are sugars or chains of sugars. Biochemists call this an aerobic process because it uses oxygen, which comes from breathing. As the exercise intensity ramps up, the body can’t get all the oxygen it needs to make ATP from breathing, so it switches to metabolizing carbohydrates without oxygen in an anaerobic process known as glycolysis. For extremely short bursts of high-intensity exercise, the body uses the phosphocreatine system, in which the enzyme creatine kinase transfers a phosphate group from stored phosphocreatine to adenosine diphosphate, thereby creating ATP.

“The soccer player is a mix of everything,” Morton says. Running up and down the pitch for 90 min or more, with periods of rest, means they use all three methods of making ATP. But, Morton says, the most important one for soccer players is the anaerobic metabolism of carbohydrates.

How glycogen boosts endurance for soccer players

Athletes store the carbohydrates they eat in muscles and in the liver as glycogen—long, branched strands of sugars with a protein core. Soccer players will use those glycogen stores during their most intense moments of play, says James Betts, codirector of the University of Bath’s Centre for Nutrition, Exercise, and Metabolism.

“Where the game is won and lost is going to be on those more intense bouts of exercise,” Betts says. Because of that, soccer players will try to have the highest levels of glycogen when they arrive for each match, he says, “and then they will try and use that as sparingly as possible during the game.”

Athletes have been using classic glycogen-loading routines since the 1960s. They essentially boost consumption of carbohydrates, things like bread, pasta, and rice, and taper their exercise. By doing this, athletes can store more than 100% of their baseline glycogen levels, as much as 10–20% more glycogen, than if they’d only rested.

“This is something that marathoners have been putting into place for years,” Betts says, and the conventional thinking used to be that it took about a week to do this. But more-recent studies show that this glycogen supercompensation can be achieved in just a few days with increased carbohydrate intake.

The day before a game, Morton says, players should typically consume 8 g of carbohydrate for every kilogram of their body mass. And then on game day, they still need to consume carbs to top off their liver glycogen, which is depleted during sleep.

But preparing for game day is only part of what World Cup players need to be thinking about. By the end of a 90-plus-min game, about half of a player’s muscle fibers have become completely depleted of glycogen, Morton says, which makes it tough to sprint. “Many goals are scored, and many bad decisions are made, as players are becoming tired,” he says.

Whether they win or lose the match, Morton says, “once you’ve finished the game and you’ve utilized all your glycogen stores, then the clock is ticking to refuel them for the next game.”

Glycogen storage is fastest in the hours immediately after exercise because muscle is more sensitive to glucose uptake, and glucose transport proteins are primed and ready to go. So players should aggressively refuel after a game, ideally consuming 1 g of carbohydrate for every kilogram of body mass every hour on the hour for 3–4 h. That’s a lot to eat, and players don’t always have the appetite. But, Morton says, “if you don’t take advantage of that opportunity, then you’re compromising your recovery.”

Betts notes that adrenaline typically leads to faster glycogen loss. Some athletes may rely on getting particularly fired up to be effective on the field, he says, “but maybe staying a bit more relaxed and not getting so fired up might help them not use so much glycogen.”

How to replenish what’s lost through sweat

Good management of salt and sweat—hydration, in other words—also biochemically boosts players’ success. That’s because the evaporation of sweat is an important mechanism for cooling the body, according to Lewis James, who leads the sport performance research group and studies human hydration at Loughborough University.

“For athletes, that can mean a lot of sweat,” James says, as much as 2 L/h during a soccer match. Determining how much sweat an athlete loses is easy, he says. “It’s a simple mass-balance equation.” Weigh the athlete before and after the match and take into account any mass they may have gained from eating or drinking or lost to urine or feces, and the difference is their sweat loss.

This year’s World Cup will take place during summer in North America, when the weather is hot, and many athletes are likely to sweat more than they would during regular season play if, for example, they’re part of a European team that typically competes in other seasons. James says it’s important to come to the tournament with a hydration strategy, which means consuming enough fluid in the days leading up to a match, not just the hour beforehand.

“The last thing you want to do is give an athlete a load of fluid and then they go onto the pitch, because for the first 45 min, they may need to pee,” James says. “That’s why we emphasize the days in advance of the match, making sure that they’re consistently consuming a good amount of fluid every day, so that they come into that match as well hydrated as possible.”

James also points out that sweat isn’t just water. It also contains electrolytes or salts, such as sodium chloride, which are important to replace as well. Salt loss via sweat can vary greatly from athlete to athlete, James says. And this is something his lab tests for.

In some athletes, a sports drink can help replace the lost salt, but for others, sports drinks may not be sufficient. They may also need to add salt to their food. “We know in the body, salt and water are pretty much paired. So, if you don’t replace the salt, you’re unlikely to replace the water,” he says.

Betts says salty foods taste amazing when you are dehydrated. “There are some sports drinks which really are very salty for when you’re dehydrated. And if you’ve been out in the heat, sweating, exercising, and you drink them, they taste incredible,” he says. “If you drink that same solution when you are rested and well hydrated, it tastes like seawater.”

As teams advance through the stages of the World Cup tournament, they will be playing games in short succession, with as little as 3 days between them. That’s still enough time for a successful carbohydrate-refueling regimen and hydration plan, but sticking to a strict recovery schedule becomes more critical than if teams are competing on a weekly schedule. So when you watch the victors in this year’s World Cup emerge, remember that the secrets to their success may include a slice of bread and a bottle of sports drink.