Last season, it was a Brazilian midfielder at Liverpool. This season, it’s been his international team-mate at Manchester United.

“I think Casemiro’s legs have gone,” Jamie Carragher told the Covering Liverpool podcast in October. “I noticed it last season at Anfield and I didn’t like what I saw. It took me back to watching Fabinho last year for Liverpool. I want to be the first to say it (about Casemiro). I don’t want to say it when everyone else is saying his legs have gone.”

Regardless of who said what and when, Carragher — who played for Liverpool until he retired at age 35 — is not a lone voice in this debate, and Fabinho and Casemiro are far from the only players singled out for seemingly having lead in their boots.

Any footballer over the age of 30 who is struggling for form leaves themselves open to that type of criticism, but in particular if they are now coming off second best in the sort of duels they used to win and playing in a way that makes it look like the game is now a split-second too quick for them.

Casemiro, who turns 32 on Friday, was at risk of straying into that territory against Luton Town yesterday. “A serial offender who kept fouling time and time again”, was the way former England midfielder Jamie Redknapp, a pundit on UK broadcaster Sky Sports’ coverage of the match, summarised his display.

Withdrawn at half-time, and fortunate in the eyes of many to have avoided a second yellow card, Casemiro is collecting bookings at quite a rate, even by his standards. He has now been cautioned in eight of his last 11 matches for club and country, and four out of five since returning from almost three months out with a hamstring injury in January.

What is clear is that the spotlight can be unforgiving for older players and, at times, unfair.

Gareth McAuley, who was still playing centre-back in the Premier League at the age of 37, viewed the “legs have gone” comment as an “easy shot” when it was directed at him at West Bromwich Albion, especially given how hard he was working to keep in shape and that it was not backed up by the data he was privy to at his club.

“I was thinking, ‘I’m doing more than people who are 10 years younger’,” the 80-cap Northern Ireland international McAuley tells The Athletic. “You think, ‘Do you know what? Show some respect’. But it’s getting even younger now: boys at 28 and 29 are being described as ‘done’.”

Not every player has reason to feel hard done by in this situation — in some cases, they are in denial.

One former international midfielder, not long retired from playing, was viewed by his coach as ‘undroppable’ because of his status. But others at the club felt the player had become a liability as he could no longer track runners and move fast enough.

Some are honest enough to hold their hands up and accept that time has caught up with them – a reality that can creep up on players during a season or, in the case of Gary Neville, be revealed in one brutal moment.

At West Brom on New Year’s Day in 2011, a 35-year-old Neville made his first start for Manchester United in two months. He describes in his autobiography how he made West Brom winger Jerome Thomas look like Cristiano Ronaldo during a deeply uncomfortable 71-minute performance in which he was lucky to avoid a red card.

Neville recalled how Mike Phelan, United’s assistant manager at the time, wandered across for a word when the ball rolled out of play close to the dugouts.

“You’re f***ed, aren’t you?” Phelan said.

Neville nodded.

Thomas, who made more than 150 appearances in the Premier League with four different clubs, remembers that game well, and also the comments Neville made later.

“I guess that was how Gary rationalised it because he was on his way out and he didn’t feel he was at his best,” Thomas says. “I don’t want this to come across the wrong way, because Gary Neville is a legend, but what he doesn’t realise is he wasn’t the only person I was doing that to. As a left-winger, I would go into every game with the goal to either get the right-back sent off or subbed.”

Jerome Thomas made Gary Neville realise his career was over (Shaun Botterill/Getty Images)

Neville would have been dismissed on another day. Instead, he was subbed. The following morning, he told United manager Sir Alex Ferguson that he was retiring. He never played for them again.

Sol Campbell, Neville’s former England team-mate, had a different experience before bringing the curtain down on his career.

“My legs never went. It was just you needed the right rest period,” Campbell, whose last match was as a 36-year-old for Newcastle United in the 2010-11 Premier League, tells The Athletic. “Once I went back to Arsenal (for a second spell midway through 2009-10), I was 35 and my numbers weren’t there, but getting back to good training helped me compete with the guys. It’s difficult, though, as you get older with the recovery. It’s hard on the body.

“If you play one game a week it’s great, but sometimes it’s four games in 10 days and that’s when you start to feel it. If you have a sympathetic manager who understands that you’re not 21 anymore, then it’s OK. So, for me, it’s not about ‘Legs gone’, it’s about recovery.”

His legs have gone.

“Sport, never mind football, is full of throwaway phrases like that,” says Chris Barnes, an experienced sports scientist who has worked for several professional clubs, starting with Middlesbrough in 1998.

“Wearing the sports scientist’s hat, one of the big challenges we have in football is getting away from focusing on averages and norms and looking at players as individuals. The reality is that phrase is appropriate (for some players) and in others, maybe not so.

“If you track a player’s journey from a physical perspective, it’s pretty widely accepted that they peak around about 26 to 28. What that means can be interpreted in a number of ways – peak is different for different players in terms of how fast they can run, their ability to do repeated high-intensity activities and so on.”

GO DEEPER

What age do players in different positions peak?

Although the data never lies, it is important to not get carried away with who runs the furthest, which is to take nothing away from the evergreen James Milner, who topped the charts at the age of 37 last season.

11.2km – Which players covered the most distance (in kilometres) per 90 minutes in the Premier League in 2022-23 (min. 900 minutes)?

11.2km – James Milner
11.2km – Brenden Aaronson
11.0km – Ryan Christie
11.0km – Christian Eriksen
11.0km – Roberto Firmino

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Ageless. pic.twitter.com/FQDvKn9GPT

— OptaJoe (@OptaJoe) May 30, 2023

“Total distance is full of noise,” Barnes adds. “The Blackburn winger (Morten Gamst) Pedersen always had the highest total distance of any game, but you must look at what is effective work and what isn’t.

“(Centre-back) Robert Huth, who was at Middlesbrough, would always come and look at how little work he’d done, because he felt his best games were performed when he made good decisions and was positionally correct and therefore the amount of work he needed to do was less. So it’s not really a ‘More is better’ situation. Football isn’t a maximal sport. It’s what typifies, if you like, the DNA, the characteristics, of a player’s game.”

How players engage with their physical data is interesting. Some bury their head in the sand or — and this was witnessed first-hand with a Premier League centre-back during a fly-on-the-wall pre-season piece a few years back — even challenge the figures. Others go actively looking for their data, to use it as a yardstick to not just inform how hard they need to work in training, but also to ensure that the manager doesn’t have an excuse to leave them out.

“The high-speed running and things like that, you get your data and they (the sports scientists) know exactly what you need to be hitting,” McAuley explains. “But in certain sessions as a defender, you won’t get what you need. So I could say, ‘OK, I need another 200 metres of high-speed running’, so I would go and run box-to-box to get that and keep me on the sports-science knife-edge between injury and peak condition.

“I had (Craig) Dawson, 10 years younger than me, who was trying to take my place, so I had to make sure I was trying to be better, trying to stay quicker. In a way, that was driving me. Also, if you weren’t in the team and you’re knocking on the manager’s door, he can’t say that your data has dropped off in training and that your legs have gone.”

SkillCorner works with around 150 clubs around the world and is at the forefront of physical data. It released some fascinating graphs on Twitter in November: the first shows the top speed of players by age during last season. In the over-30s category, Manchester City’s Kyle Walker, 33, remained the fastest player, while both Jamie Vardy and Ashley Young, who are now 37 and 38 years old respectively, were way above the average for their age.

That said, it is also worth remembering Barnes’ comment about the importance of analysing players as individuals and against their own benchmarks rather than comparing them to others.

Every Premier League club will have access to this kind of data and, crucially, will be able to see how a player’s physical levels go up and down over time.

This next SkillCorner chart gives a glimpse of what that looks like — in this instance, it shows Dani Carvajal, the now 32-year-old Spain and Real Madrid right-back. Carvajal’s high-intensity activities per 90 minutes are represented game-by-game and there is also a season average, measuring what SkillCorner describes as “a player’s longitudinal physical performance”.

Of course, there are other factors to take into consideration, especially when analysing an extended period. Managerial, tactical and positional changes can all impact the physical data gathered in matches.

“In training, the sports scientists have a responsibility to be looking at appropriate data to give a mark on the condition of the players they’re working with, and that would involve things like recovery between bouts — heart-rate data is super-informative in things like that,” Barnes adds.

“These high-intensity actions and efforts are the key and unlock a better understanding as to whether the qualities and characteristics of a player have changed. But you definitely have to take into account the tactical context: how the game is evolving and how coaches want it to be played.

“It’s been widely documented how the physicality of Manchester City’s game has grown year on year with Pep Guardiola’s philosophy and Kyle Walker has been able to fit into that. If anything, it’s provided a platform for him to showcase the qualities he possesses even more.”

“You play football with your head and your legs are there to help you.” – Johan Cruyff

Peter Taylor was singing from that hymn sheet when he brought Roberto Mancini to Leicester City in 2001, Taylor, the club’s manager at the time, openly admitted he signed the 36-year-old Italian forward “for his football knowledge, not his legs”. Chelsea clearly felt the same way about Thiago Silva joining them at the age of 35.

Barnes talks about how “game intelligence continues to increase” and, at times, can compensate for the ageing process, but he also points to a 2015 study that he was involved in looking at “longitudinal match performance characteristics of UK and non-UK players in the English Premier League” and the hard evidence that football at the highest level had become “seriously more demanding from the point of view of the high-intensity requirements”.

“SkillCorner has carried on that work and brought it up to date and that has shown that the demands of competing in the game have grown again,” Barnes adds.

“Gary Neville, Kyle Walker and Dani Carvajal are interesting examples, because they’re all right full-backs, and I would argue that full-back and striker are where this evolution has been most dramatic in terms of requirements to play the game.”

Kyle Walker’s athleticism remains undimmed (Justin Setterfield/Getty Images)

For a No 6 in the modern era, the skill set and the physical demands are huge.

“In this position, you need a guy who wins challenges and protects everybody, but who plays football as well,” Jurgen Klopp, Liverpool’s manager, said last season. “Fab (Fabinho) did that for us for plenty of years (and was) absolutely brilliant. At the moment, it’s not clicking. We have to go through that.”

Outside the club, pundits were quick to judge what had gone wrong with Fabinho. “You know when you’re a midfielder and your legs just start to go and you can’t get around the pitch as much as you would like, that’s what it seems to be,” Micah Richards, the former Manchester City defender, told BBC Sport.

Defensively, Fabinho’s output did drop last season. According to Opta, he was recovering the ball less, winning fewer duels and not making as many interceptions, which helps explain why Liverpool were happy to cash in on him in the summer. With Casemiro, his data shows he is making fewer interceptions in the Premier League this season compared to last (down from 1.4 per game to 0.9) and winning possession on fewer occasions too (down from 8.7 per game to 6.0).

Of course, none of those statistics can be seen in isolation. Last season at Liverpool, for example, Fabinho was far from the only player struggling for form. There is also the question of the team setup and how much that leaves a player exposed. Casemiro, in now Sky pundit Gary Neville’s words, was “absolutely torn to shreds” against Wolves in the first match of this season — a comment that was an indictment of the shape of United’s midfield as much as anything.

In the absence of detailed physical data to prove otherwise, people will draw their own conclusions from what they see during matches (just as managers used to do before the sports-science revolution) and it doesn’t take much for a narrative to take hold, especially when a player is in their thirties.

The sight of 20-year-old Jamal Musiala skipping away from Casemiro three times in the space of seven minutes during United’s 4-3 defeat against Bayern Munich in the Champions League earlier in the season (albeit the Brazilian scored twice that night) provided one of those moments.

In reality, Casemiro was always going to be an easy target for the “legs have gone” narrative, mindful of the reaction when United agreed to pay Real Madrid £70million ($88.2m at current rates) for a 30-year-old in summer 2022. Even INEOS, United’s new investors, were surprised at the numbers involved in the deal.

As a counterpoint, it is important to remember that Casemiro performed really well for United in that debut season and with more time to get up to speed after his recent injury, and with the hugely impressive teenager Kobbie Mainoo operating in the same midfield, there is an argument he could still be an important player at Old Trafford.

Either way, it’s a matter of time before the same four words are levelled at someone else.

McAuley smiles. “I think that (phrase) is kind of deep-rooted in pre-sports-science football,” he adds.

“Do the legs go? Maybe. But what I would say is that it’s the desire to keep doing it — the mental side. You can tell yourself to do anything. And with the mind and the willpower to do it, you can.”

(Top photos: Getty Images; design: Eamonn Dalton)