Jannik Sinner’s Wimbledon fitness concern: The science behind competing in extreme heat

One of the biggest question marks heading into this year’s Wimbledon is whether or not Jannik Sinner will be struck down with physical issues from the heat.

Had it not been for the Australian Open’s extreme heat protocols, which led to an eight-minute break and the roof being closed, Sinner would most likely have lost to Eliot Spizzirri in the third round. 

And just when he looked on course for a comfortable straight-sets victory over Juan Manuel Cerundolo in the second round at Roland Garros, the Italian suffered a physical collapse before losing in five.

Since then, Sinner has reportedly undergone medical checks to get to the root of this matter, although slightly cooler temperatures at Wimbledon may save the world No 1.

Even though these are some of the best athletes on the planet, extreme heat can affect anyone. To find out more, Tennis365 spoke to Professor James Morton, who is a professor of exercise metabolism at Liverpool John Moores University.

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Can you talk about why performance deteriorates in high temperatures and what the knock-on effects are?

Professor Morton, who was a performance nutritionist at Liverpool FC from 2010-15, explained the science behind what happens to an athlete’s body on a scorching hot day.

He said, “Performing in the heat is one of the toughest physiological challenges an athlete can face, and this is definitely the case for professional tennis players.

“While resting core body temperature is typically around 37°C, prolonged high-intensity exercise can increase this to 39°C (or even higher in extreme circumstances). In addition to this, core temperature rises more rapidly when exercising in hot conditions and can be 0.5°C higher than during the same exercise in cooler environments.

“In order to limit this rise in temperature, the body increases blood flow to the skin and sweat rate increases in attempt to dissipate heat. While these responses are essential for cooling down, they also cause a physiological dilemma because the cardiovascular system must simultaneously supply blood to working muscles to deliver oxygen and fuel. The result is essentially a competition between cooling and performance.

“Muscles also rely heavily on carbohydrate as a fuel source which can be particularly problematic in a sport like tennis where matches can go on for several hours. Muscle glycogen stores are limited, and exercise in the heat can accelerate their depletion. As glycogen availability declines, players may experience reductions in physical and technical performance.

“Ultimately, heat does not just make tennis players uncomfortable, it increases cardiovascular, metabolic and cognitive strain simultaneously, which is why both performance and welfare become major concerns in extreme heat. ”

How does the brain reduce muscle activation as a protective response?

Players, pundits, and fans alike often debate whether or not a physical collapse comes from the mind giving up or the body.

But according to Professor Morton, who is the chief science officer at Science in Sport, the mind tells the body what to do and not the other way around.

“It’s important to remember that all movement begins with the brain. The brain sends signals to the muscles to move in the first instance, which then send back signals to the brain to regulate performance in the given task,” he said.

“As well as occurring within the muscle itself, fatigue can occur in the nervous system, which means the brain appears to reduce neural drive to the working muscles, resulting in a decline in force production and exercise performance.

“This phenomenon is often referred to as central fatigue and becomes more exaggerated in the heat. It’s thought to be a protective response to rising physiological strain. As core and brain temperatures increase, reducing muscle activation may help limit further heat production and reduce the risk of potentially dangerous levels of thermal stress.

“While the precise role of central fatigue as a regulator of exercise performance remains an active area of scientific debate, there is strong evidence that heat stress amplifies central fatigue.

“This could explain why many athletes report their legs feeling heavy, their movements becoming less explosive, and sustaining high intensity efforts becomes increasingly difficult in hot conditions, even when motivation remains high.”

How can tennis players combat the heat with hydration and fuelling strategies?

During a tennis match, players can be seen with ice packs, various drinks and snacks, and even pickle juice is guzzled down by the top stars as a way to beat cramp. Indeed, players can lose several litres of sweat every hour, so staying on top of this is essential.

Professor Morton, who was nutrition and physical performance lead for Team Sky between 2015 and 2019, said, “The most effective strategies are likely to occur before the first ball is struck. Starting each match hydrated and fully fuelled should never be taken for granted, yet it’s still a mistake that even the best athletes in the world often make.

“Given our limited ability to store carbohydrates, the importance of consuming carbohydrates during exercise cannot be underestimated. You will often see professional players consume carbohydrates in breaks between games, often in the form of food, gels or drinks.

“This is all for good reason – not only to maintain carbohydrate delivery to the muscle, but also to maintain glucose supply to the brain and prevent players from becoming low in blood glucose (which is another cause of fatigue).

“In high heat conditions, reducing your resting core temperature before you exercise can increase thermal gradient between the core and the ambient air, increasing the capacity to dissipate heat during exercise.

“You will often see athletes using ice vests, ice towels and even consuming ice slushies before exercise – this all has the goal of reducing your core temperature. Some of these cooling strategies may also be applied during designated heat breaks.

“Of course, hydration is equally important. Particularly in hot conditions where sweat losses can be substantial. In some cases, tennis players could lose two to three litres per hour.

“Ultimately successful performance in hot conditions is rarely determined by a single strategy. It is usually the combination of appropriate fuelling, hydration, electrolyte replacement, cooling, and heat acclimation which provides the greatest protection against fatigue and performance decline.”

What do you make of Sinner’s physical struggles, particularly at the French Open and then last year in Shanghai? Andre Agassi criticised his conditioning after his Roland Garros loss, where he hit the wall before the two-hour mark. What should he do to combat this? Should he change his routine?

Sinner will have been speaking to some leading experts trying to make sure that there is no repeat of what happened in Australia and France.

And according to Professor Morton, training harder may not be the best answer. Indeed, nutrition, fuelling and recovery may be more important.

He added, “I wouldn’t want to comment on specific athletes, and of course there are many different causes to fatigue beyond conditioning alone, including environmental conditions, fuelling and hydration.

“Tennis is one of the most energetically demanding sports that we have ever studied. In fact, at Liverpool John Moores University we did a series of studies several years ago, led by Doctor Dan Ellis, quantifying the energy expenditure of players during training and tournament weeks (including Wimbledon).

“Data demonstrated daily energy expenditures of 4,000 and 5,000 calories from females and males. The unpredictability of tournament match play duration can also affect energetic demand considerably, shorten recovery times, and increase both the physical and cognitive load that placed on players.

“Top players clearly need the physiological capacity to perform such high daily workloads. This is the training component of the performance equation.

“However, in the more modern era of sport, it is becoming increasingly recognised that the nutritional component of performance that can really be the difference between winning and losing. The performance solution may not always be to train harder, but to fuel and recover better.”

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