[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 Dec

The 2026 FIFA North American World Cup will kick off on June 11 at Estadio Azteca in Mexico City. Taking place across 16 cities in the United States, Canada, and Mexico until July 19, this tournament is expected to be the hottest World Cup in history, with temperatures in some regions nearing 40 degrees Celsius. High-altitude stadiums, such as those in Mexico City at around 2,200 meters above sea level, are also expected to present significant challenges.

As a result, heatwaves and player safety have become major topics of discussion outside the stadiums, while inside, aerodynamics, sports physiology, and recovery science have become critical variables that can determine the outcome of matches. International researchers warn, "The strongest opponent at this tournament could be the heatwave." Recently, a research team from the World Weather Attribution (WWA) also analyzed that the heat stress risk for certain matches might 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

Soccer is no longer a simple test of physical strength. Everything—from the trajectory of the ball to body temperature, heart rate, and muscle recovery—is within the realm of science. The same shot can travel differently depending on altitude and air density, and the same temperature can pose vastly different physical strains depending on humidity and wind. This World Cup offers the most dramatic display yet of how sports and technology come together.

The Physics Behind the Curving Ball

The scene where a ball bends around the defensive wall and finds the corner of the goal during a free kick is the result of precise physics.

A key principle at play is the "Magnus effect." When a spinning ball creates a difference in airflow speed around it, a pressure difference follows. The ball is then pulled toward areas of lower pressure, causing it to curve. Curveballs in baseball and banana kicks in soccer follow the same principle.

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 Seongchan of the Department of Sports and Exercise Science at Seoul Women's University explains, "The farther the impact point between the ball and the foot is from the ball's center, the greater the rotational force, but the forward velocity decreases. Players intuitively adjust the balance between spin and speed depending on the game situation."

Free kicks by players like David Beckham and Son Heung-min are far from mere luck. The amount of spin and speed—and thus the flight path—are determined by exactly where the foot strikes the ball. World-class kickers excel at finding the optimal balance between spin and velocity in an instant.

Why the Knuckleball Is Even More Fearsome

On the other hand, a "knuckleball"—a shot with almost no spin—harnesses a different branch of science. This specialty of Cristiano Ronaldo deliberately creates unstable airflow around the ball.

Professor Hong explains, "The knuckleball creates turbulent vortices (the Karman effect) behind the ball that move unpredictably, causing the ball to wobble violently up, down, and sideways." Unlike a curling shot, whose trajectory can be predicted, a knuckleball is difficult for goalkeepers to judge until the very last moment.

The official World Cup ball becomes a subject of scientific debate with every tournament for the same reasons. The panel structure, seams, and groove depth completely change air resistance and flow. The "Jabulani," official ball of the 2010 South Africa World Cup, was a prime example. Goalkeepers infamously complained that "it feels alive, and you never know where it will bounce."

Professor Hong added, "Changing the panel shape and seam structure shifts the 'separation point' where the airflow detaches from the ball's surface, which fundamentally changes its flight characteristics."

At High Altitude, the Ball Flies Differently

The biggest geographical variable at this North American World Cup is altitude. The opening match venue, Mexico City, sits at an extreme 2,200 meters above sea level.

With increasing altitude comes lower atmospheric pressure and thinner air. Professor Hong explains, "Even at about 1,500 meters, air density drops by around 10% compared to sea level, and at over 2,000 meters, it can decrease by nearly 20%. In these conditions, air resistance drops, so the ball travels faster and farther, and it comes down later than usual."

This means balls travel farther and faster, while spinning shots curve less, and the unpredictable movement of knuckleballs diminishes. Relying solely on sea-level instincts can easily send shots and passes flying over the goal.

High altitude also disrupts athletes’ biological rhythms. Lower air pressure means less oxygen is taken in with each breath. Even maintaining the same work rate, athletes get short of breath faster and recover more slowly, which is why national teams place so much emphasis on pre-tournament altitude training.

How Do Players Survive 40-Degree Heat?

Heatwaves driven by the climate crisis, with temperatures around 40 degrees Celsius, represent the greatest threat at this tournament. Soccer is an extreme sport, demanding maximal sprints, deceleration, and sharp directional changes over 90 minutes.

Park Dooyong, Research Fellow at the Next-Generation Sports Science Support Center of the Korea Institute of Sport Science, explains, "The core physical factor that determines soccer performance is the 'Repeated Sprint Ability' (RSA). Victory goes to the team that can repeat high-intensity sprints most frequently and recover the fastest between them."

The real problem is humidity rather than temperature. Our bodies cool by evaporating sweat, but in a hot and humid environment, sweat does not evaporate well, paralyzing the body's cooling system. Park warns, "High humidity is far more dangerous for internal temperature increases than a dry environment."

This is why sports medicine professionals use Wet Bulb Globe Temperature (WBGT) rather than just air temperature. WBGT calculates the heat load humans experience by combining temperature, humidity, radiant heat, and wind speed. WWA researchers concluded that some World Cup matches may be played in WBGT conditions above 26 degrees, and at times, it could hit the 28-degree threshold— the benchmark that soccer unions use to postpone matches. FIFA and the International Olympic Committee (IOC) also base their heat response decisions on this measure.

Mike Tipton, a professor at the University of Portsmouth, UK, urged FIFA to strengthen protection standards, warning, "Soccer played in extremely high temperatures can not only reduce performance but also trigger acute medical emergencies such as heatstroke, endangering players' lives."

After the 75th Minute, Physical Fuel Runs Dry

Past the 75th minute, even veteran players display more passing mistakes and become noticeably sluggish. While fans often blame 'loss of mental focus,' the real cause lies in clear physiological limits, not mental weakness.

Just as a car needs gasoline, human muscles use glycogen as the main energy source during high-intensity activity. Repeated sprints over 90 minutes can deplete these stores. Add a heatwave to the equation, and dehydration and rising internal temperature cause glycogen depletion to occur several times faster than normal.

When the body’s temperature control function nears its limit, a survival mode kicks in: blood flow destined for the heart and muscles is rerouted to the skin’s surface to release heat. As a result, highly active muscles receive less oxygen, reducing efficiency and causing heart rates to soar. Meanwhile, blood flow to the brain decreases, leading to loss of judgment and focus. This is the scientific reason why crucial defensive mistakes often occur at the end of matches.

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

This is not a problem unique to soccer. Heatwaves brought by the climate crisis already threaten athletes in all sports worldwide. Tennis players at the French Open described, "Standing on court, it feels like you’re not fighting your opponent, but battling the giant sun above you and the heat inside your body." Russia’s Daniil Medvedev even shouted at a camera mid-match, "Will someone have to die before you wake up?" in a moment of exasperation.

Indeed, when internal body temperature exceeds 40 degrees Celsius, a player is at risk of heat stroke, an extreme condition marked by loss of consciousness and circulatory failure that can endanger life itself.

The football world is no exception to these dangers. During the Qatar World Cup, England midfielder Declan Rice confessed, "By the second half, my mouth was completely dry and my head cloudy. Even though I wanted to move, it felt like the signal from my brain to my muscles was completely cut off—the legs just wouldn’t go." This is why, at the upcoming North American World Cup, national teams are as committed to temperature control and hydration strategies as they are to tactical planning.

Victory Is Decided by Recovery, Not Stamina

In modern soccer, "how hard you run" is matched in importance by "how quickly you recover." Recovery has become a matter of science, not just willpower.

Players start managing body temperature even before kickoff—wearing cooling vests to slow internal temperature rise, and carefully monitoring hydration. During games, they use ice towels and take cooling breaks. Immediately post-match, they plunge into ice baths at around 10 degrees Celsius to suppress muscle inflammation and forcibly lower body temperature.

Portuguese goalkeeper Patricio. Photo by UEFA Official Website

Rehydration is more precise than ever. The amount of fluid and electrolytes (such as sodium and potassium) lost through sweat is measured in real time so players can be given personalized drinks. GPS sensors and wearables attached to uniforms transmit real-time data to the bench, including distance covered, top speed, heart rate variability (HRV), and fatigue index.

Research Fellow Park notes, "Recently, AI technology is used to analyze individual movement pattern data and injury history of players, enabling prediction of injury risk and adjustment of playing time." Thorough "data science" has now replaced coaches' intuition and players’ willpower in physical management.

At the 2026 North American World Cup, players must battle not only opposing defenders, but also air density, thin oxygen, 40-degree heat, and the invisible threats of internal dehydration and fatigue toxins. Ultimately, the team that smiles last in this vast physical and physiological laboratory will be the one that best understands and harnesses science.

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