[Science Scope] 40-Degree Heatwaves and 1,500m Altitude: The World Cup Battles Science

Why Does the Ball Curve and Players Tire?
How Aerodynamics, Heatwaves, and Recovery Science Are Transforming Modern Football


From Knuckleball Shots to Glycogen Depletion and Altitude Acclimatization:
The Invisible Variables That Decide Victory

The 2026 FIFA North American World Cup will kick off on June 11 at Estadio Azteca in Mexico City. This tournament, held across 16 cities in the United States, Canada, and Mexico until July 19, is expected to be the hottest World Cup in history, with temperatures in some regions approaching 40 degrees Celsius. High-altitude stadiums, such as in Mexico City at an elevation of 2,200 meters, also present unique challenges.

Accordingly, heatwaves and player safety have become pressing issues off the pitch, while aerodynamics, sports physiology, and recovery science have emerged as decisive variables within the game. International researchers warn, “The strongest opponent at this tournament could be the heatwave.” Recently, the World Weather Attribution (WWA) research team also analyzed that the heat stress risk for some matches would exceed the safety standards set by the International Federation of Professional Footballers (FIFPRO).

On the afternoon of the 25th (local time), national football team coach Hong Myung-bo and players are warming up at the Zion’s Bank Training Center located in Herriman, Utah, USA. Photo by Yonhap News

Football is no longer a simple contest of endurance. Everything from the trajectory of the ball to body temperature, heart rate, and muscle recovery now falls within the realm of science. The same shot will fly differently depending on altitude and air density, and the physical burden on players will vary dramatically with changes in humidity and wind, even at identical temperatures. This World Cup is the most dramatic stage yet for showcasing how sports and science converge.

Physics Behind the Curving Ball

The moment when a ball curves around the defensive wall and rockets into the corner of the goal during a free kick is the result of precise physics.

The primary principle is the “Magnus Effect.” When a spinning ball creates a difference in air flow speed around its surface, a pressure differential arises. The ball is then pulled toward the area of lower pressure, causing it to curve. This is the same principle behind a baseball curveball or a football banana kick.

Sprinklers are operating before the game to control the grass surface temperature and moisture levels. In modern soccer, not only the players' condition but also the moisture content and surface temperature of the grass are scientifically managed. Photo by Unsplash

Professor Hong Sungchan from the Department of Sports Exercise Science at Seoul Women's University explained, “The farther the point of impact between the foot and the ball is from the center of the ball, the greater the spin, but the forward velocity decreases. Players intuitively adjust the balance between spin and speed according to the situation on the field.”

Free kicks by players like David Beckham or Son Heungmin are not the result of mere luck. The amount of spin and speed—and thus the flight path—are determined by which part of the ball the foot strikes. World-class free kickers have an exceptional ability to instantaneously find the optimal balance between spin and speed.

Why the Knuckleball Is Even More Dangerous

In contrast, the “knuckleball,” a shot delivered with minimal spin, employs a different scientific principle. This technique, a trademark of Cristiano Ronaldo, intentionally creates turbulent, unstable airflow around the ball.

Professor Hong explained, “A knuckleball creates an irregular air vortex (Karman effect) behind the ball, causing it to unpredictably swerve up, down, left, and right.” Unlike a curling shot, whose trajectory can be anticipated, it is extremely difficult for goalkeepers to judge the direction of a knuckleball until the very last moment.

This is also why the official World Cup match ball becomes a focus of scientific debate every tournament. The panel design, seam configuration, and groove depth on the ball’s surface can completely alter air resistance and flow. The “Jabulani,” the official match ball of the 2010 South Africa World Cup, is a prime example. Goalkeepers at that time lamented, “The ball seems alive, bouncing unpredictably in all directions.”

Professor Hong added, “When the panel shape and seam structure change, the ‘separation point’—where airflow detaches from the surface—also shifts, completely altering the ball’s flight characteristics.”

At High Altitude, Even the Ball Flies Differently

The greatest geographic variable at this North American World Cup is elevation. The opening match will be held in Mexico City, which sits at about 2,200 meters above sea level—a very high altitude.

As altitude increases, atmospheric pressure decreases and air density becomes thinner. Professor Hong explained, “Even at highlands of 1,500 meters, air density drops by about 10% compared to sea level; above 2,000 meters, it can decrease by nearly 20%. In such conditions, reduced air resistance makes the ball fly faster and farther, and it takes longer to descend.”

In other words, the ball travels farther and faster, but spinning shots, which rely on air resistance to curve, bend less, and knuckleballs wobble less. Relying only on one’s usual sense of distance can cause passes and shots to easily overshoot the goal.

High altitudes also disrupt athletes’ biological rhythms. Lower air pressure reduces the amount of oxygen intake per breath. This means players tire more quickly and recover from fatigue more slowly, even at the same intensity. That’s why national teams devote so much attention to altitude acclimatization training before matches.

How Do Players Endure 40-Degree Heatwaves?

Heatwaves of around 40 degrees Celsius, caused by the climate crisis, are the biggest adversary at this tournament. Football is an extreme sport, demanding 90 minutes of repeated all-out sprints, deceleration, and sudden changes of direction.

Park Dooyong, research fellow at the Next Generation Sports Science Support Center at the Korea Institute of Sport Science, explained, “The key physical factor determining football performance is repeated sprint ability (RSA). The outcome hinges on how often players can sprint at maximum intensity and how quickly they recover in between.”

The bigger problem, however, is not temperature but humidity. The human body cools itself by evaporating sweat, but in hot and humid conditions, sweat does not evaporate, leading to a breakdown of the body’s cooling system. Park warned, “High humidity is much more dangerous for core body temperature than dry heat.”

This is why sports medicine uses wet-bulb globe temperature (WBGT) instead of just air temperature. WBGT combines temperature, humidity, radiant heat, and wind speed to indicate the actual heat load felt by the human body. WWA researchers concluded that some World Cup matches may be played with WBGT above 26 degrees, and some may reach 28 degrees, the threshold at which player unions call for match postponements. FIFA and the International Olympic Committee (IOC) also use this measure to determine heat response strategies.

Mike Tipton, professor at the University of Portsmouth in the United Kingdom, urged FIFA to strengthen protection standards, saying, “Playing football in high temperatures can lead not only to performance decline but also to medical emergencies such as heat stroke, endangering players’ lives.”

After the 75th Minute, the Body’s Fuel Runs Out

After the 75th minute of a match, even veteran players start to make more passing errors and their movements visibly slow down. Fans often attribute this to a lack of mental strength, but in fact, it is a clear physiological limitation, not a psychological one.

Just as cars require gasoline, human muscles use glycogen as their main energy source during high-intensity exercise. Repeated sprints over 90 minutes deplete these energy reserves. If this is compounded by a heatwave, dehydration and rising body temperature accelerate glycogen depletion several times faster than usual.

As the body’s cooling mechanisms reach their limit, it shifts into emergency mode to survive. Blood that should be going to the heart and muscles is redirected to the skin surface to dissipate heat. As a result, oxygen supply to the working muscles drops sharply, reducing efficiency and causing heart rate to soar. At the same time, decreased blood flow to the brain impairs judgment and concentration, which is why costly defensive mistakes often occur late in the game.

A soccer player lying on the ground due to exhaustion. Photo by Pixabay

This is not a problem unique to football. Heatwaves caused by the climate crisis are already threatening athletes worldwide. Players at the French Open tennis tournament told reporters, “Standing on the court, it feels like you’re battling not your opponent, but the scorching sun above and the heat within your own body.” Russia’s Daniil Medvedev even lashed out at a broadcast camera during a match, saying, “Someone’s going to have to die before you take this seriously.”

In fact, when core body temperature exceeds 40 degrees Celsius, the situation becomes critical: this is “heat stroke.” At this stage, players can experience loss of consciousness and circulatory problems, which can be life-threatening.

The football world is not immune to this danger. Declan Rice, a key midfielder for England during the last Qatar World Cup, admitted, “After halftime, my mouth would get dry and my head would go fuzzy. Even when I wanted to move, it felt as if the signal from my brain to my legs had been cut off.” This is precisely why national teams at this North American World Cup are investing as much in body temperature management and hydration strategies as in tactics.

Recovery, Not Stamina, Decides the Outcome

In modern football, “how hard you run” is just as important as “how quickly you recover.” Recovery is now a matter of science, not just willpower.

Players begin managing their body temperature even before kickoff, wearing cooling vests to slow the rise in core temperature and checking their hydration status. During matches, they use ice towels and take cooling breaks. Immediately after the game, they immerse themselves in ice baths at around 10 degrees Celsius to suppress muscle inflammation and rapidly lower body temperature.

Portuguese goalkeeper Patricio. Photo by UEFA Official Website

Hydration strategies have also become more precise. The amount of fluid and electrolytes (such as sodium and potassium) lost through sweat is measured in real-time, and players are prescribed personalized drinks. GPS sensors and wearable devices attached to uniforms transmit data to the bench in real-time, including distance covered, top speed, heart rate variability (HRV), and fatigue index.

Park explained, “Recently, artificial intelligence (AI) has been used to analyze players’ movement patterns and injury histories to predict injury risk and adjust playing time.” Whereas physical management used to rely on a coach’s intuition and a player’s determination, it is now based on thorough data science.

At the 2026 North American World Cup, players will be fighting not only opposing defenders, but also air density, thin oxygen, 40-degree heatwaves, and invisible internal dehydration and fatigue toxins. In this vast physical and physiological laboratory, the team that ultimately triumphs will be the one that understands and leverages science best.

This content was produced with the assistance of AI translation services.