How much is too much? It's a question people are asking more frequently with regard to young footballers, as some of the game's biggest breakthrough stars are racking up thousands of minutes before they turn 21.
The issue rose to prominence once again during the last international break as 19-year-old Barcelona and Spain star Gavi sustained a serious knee injury during his 27th-straight game for his nation. (He now faces roughly 10 months on the sidelines after surgery.)
It's something Spain has experience with before, as his Barcelona teammate Pedri took to the pitch an incredible 73 times for club and country in the 2020-21 season. That is an achievement proudly displayed on Barcelona's website -- along with a little note to say he played the first two games of the following season before being granted a two-week holiday -- but a succession of hamstring injuries have hampered his development ever since.
Is playing this many games healthy at such a young age? Are players being put at risk? Will it shorten their career as a result? For the likes of Pedri, Gavi, Arsenal's Bukayo Saka and Real Madrid's Jude Bellingham these are important questions.
Case Study 1: Bukayo Saka
In October, Arsenal's 22-year-old winger missed his first Premier League game in over two years, snapping a remarkable streak of playing 87 successive top-flight matches -- with domestic and European cup games adding to that total as well.
Many Arsenal fans on social media have been calling for Saka to get a rest, miss a game, or be substituted once the club are comfortable in a game. But he continues to amass minutes regardless of the fixture, and has 1,037 from his 12 games this season already -- only behind midfielder Declan Rice (1,114) and centre-back William Saliba (who has played every minute for 1,170).
Fans may be confused why Saka has not been rested given he has played 147 times for 11,539 minutes since his breakthrough in November 2018 (and every game of the past two seasons), but according to Callum Walsh, an experienced conditioning coach and former Head of Sports Science at Newcastle United, the winger's body simply hasn't given off the warning signs that the club's sports scientists are watching for.
"Saka has shown he's very robust," he tells ESPN. "He burst onto the scene and has played all the time; he's shown he can handle starting every game. If that's the case, why wouldn't you start him? I've worked with more than 20 different managers. Most worry about their jobs; not many can afford to not play their best players because there's so much pressure on them at the top level. There's hundreds of millions of pounds at stake. Saka is a star player, so he plays."
Walsh says Arsenal's medical staff will be looking for the first signal that an injury could occur -- that may come from a barrage of medical tests including blood work, sleep analysis, muscle recovery, or just how the player feels. One came recently for Saka, snapping that 87-game streak, but it only kept him out for one game, which won't be deemed significant.
"Once you get that first warning signal, that's where you need to act, start thinking ahead and managing a player's fitness," he says. "Then when you're also in European competition and the player plays for his country, it becomes really complicated. You start asking: 'Where can we get them a bit of a break?' Not just physically, but there's a mental refresh part to it too."
However, it's more complicated than just giving him a rest. Footballers are finely tuned, elite athletes whose bodies run via a consistent rhythm. Saka's rhythm, for example, is to play three times a week; he'll likely do very little "grass time" (intense training) and his body is used to that, just as it's used to playing a lot.
Incredibly, giving Saka a random rest in the middle of the week, or a game off, could mess with his cadence to the point it actually causes injury. There's such a thing as too much high intensity running, but there's also such a thing as too little. A sudden spike (or drop) can cause a problem.
"The best thing a footballer can do, for his fitness, is play football," Walsh adds. "If someone is really robust and you can get them into a nice rhythm, do it. Saka had the same Physical Performance Coach (Sam Wilson) with him from the developmental age groups all the way through to the first team; so not only is that great continuity of athletic programming, but someone who knows the athlete inside-out and has six to eight years' worth of data."
Very few clubs have this luxury of continuity and understanding, as sports scientists and fitness coaches drift from job to job, inherit new scenarios and may need to build up a level of understanding with their squad. Major complications can also arise with the tug of war between club and country, as well as an ever-increasing calendar of games, meaning it's hard to find a moment to give players the break they might need.
We're perhaps seeing this with Saka too, as England boss Gareth Southgate consistently picks and plays him for his country. But at least with Arsenal he has a deep understanding and relationship, which means, in the short-term at least, all is well.
Case Study 2: Pedri
There is no doubt that Pedri's body has fired off the warnings Walsh is talking about. In fact, it's done it multiple times. The Barcelona midfielder has already sustained five separate hamstring injuries by age 20.
Reports in Spain suggest the Catalan club are now extremely worried about him and are having to be very careful with how quickly they bring him back from his latest problem. Since 2020, Pedri has played 151 times for Spain (including at U23 and U21 level) and Barcelona for a total of 10,825 minutes. Almost half came in that 2020-21 season (plus the first two games of 2021-22) when he played 75 times for 5,273 minutes -- and he was a starter in 57 games.
"Players get to a point where they self-regulate, which means they break," Walsh says. "The body is saying 'I cannot do this anymore.' The problem is once that's happened, it's already too late. A chronically bad hamstring at 20 can impact on lots of things. It changes your future injury risk. It can change your running mechanics, which puts stress on other muscles. By 23, you could have a chronic adductor or knee issue. Pedri might come through this period and have no other issues, but he might not. In the end, it's probably going to catch up with you."
Just before the last November international break, Pedri made his first start since August for Barcelona against Alaves. But the club reportedly then spent the following week fighting off the Spanish federation's attempts to call him up to the national side for games against Cyprus and Georgia, despite the fact Spain have already qualified for Euro 2024.
The club-vs.-country battle is nothing new, but it's almost impossible to balance a star player's fitness with the needs of the squad for both teams. Walsh calls it "the hamster wheel," which is apt, given the reason there's concern is that young players are just being asked to run, run, and run some more.
For his part, Gavi has played a remarkably similar number of games and minutes for Spain (including at U23 and U21 level) and Barcelona to his teammate: 151 games for 10,210 minutes.
Are players' careers going to get shorter?
Scientifically speaking, there's little to worry about regarding Saka right now. There's loads to worry about with Pedri, but that ship may have sailed. There's a key distinction to make, though: Saka being managed week-to-week well now doesn't change the fact he's playing a lot of football at a young age and that could change the shape of his career -- most notably where he peaks, and when he begins to decline.
Strikers tend to peak in their early 20s, midfielders in their mid-to-late-20s, and defenders in their late 20s or early 30s. But in an increasingly physical and frenetic game, where players are consistently involved in senior football from age 16 or 17, suggests those goalposts may be shifting.
"Think of it like miles on the clock [in a car]," Walsh says. "3,000 minutes used to be a good season; 3,500 minutes was a phenomenal one -- it meant you started most weeks, avoided major injury and didn't get suspended much. Now guys like [Bayern Munich striker] Harry Kane, [Man City midfielder] Rodri and [Liverpool forward] Mohamed Salah are playing 5,000 or 6,000 minutes per season. It is just not sustainable. They are not Formula One cars, where you whack the wheels on, go as fast as you can, then once the grip has gone, say 'see ya later' and stick new ones on. It does not work like that."
Kane was already 21 when he made his Premier League debut for Tottenham, while Salah was just leaving FC Basel in Switzerland for an ill-fated spell at Chelsea at the same age. But what does it mean for youngsters who are not only starting their careers earlier, but are playing more high-pressure matches at that age?
"The age profile of players is shifting," says Walsh. "Careers aren't the same as they used to be. The age peak is changing: it has shifted forward [earlier], or it hasn't shifted but has actually been crammed into a six-year period."
Across European football, you can see hints of this in action. There are players who broke through as teenagers a decade ago now hitting their late-20s or early 30s and slowing down, either due to elements of physical decline and injury, or perhaps due to the mental pressure that playing top-level football entails.
The table below shows players (excluding goalkeepers) who are now over the age of 30, but played the most minutes in their respective leagues between 15-20 since 2010. Few are still playing at their highest level and many have a long history of injuries, after they started playing top-level football every week as teenagers.
For example: Chelsea striker Romelu Lukaku (30) has spent the last few years struggling to find fitness and form in a succession of loans; Manchester United defender Raphaël Varane (30) has been hit by a number of injures; while former Real Madrid winger Eden Hazard (32) retired because his body couldn't go on any longer. The likes of former Manchester United defender Phil Jones and Arsenal midfielder Jack Wilshere offer further cautionary tales of careers being cut short.
Among the current group, the top 10 have all played more minutes than Jones did. And for some -- namely Pedri, Wirtz and Hickey -- that has already included a spell out with a significant injury.
That said, this is by no means a guarantee that these young stars are fated for an early decline. Walsh has a long list of different factors that mean every player and situation is unique, including: genetics, which position you play, which role you play within that position (central centre-back in a back three is very different to an outside centre-back), which league you play in, what surfaces you play on, and whether you play for a dominant team.
That latter point might help explain the incredible longevity in some elite players' careers, like Real Madrid's Luka Modrić or former Man United winger Ryan Giggs, and might bode well for our young stars in question, considering they play for dominant sides.
But Gavi's ACL tear has given us a fresh reminder of how it can all come crashing down in an instant. Being a key player for both club and country before you turn 21 can lead to problems if you are never allowed off the hamster wheel.