For football players, their body is their currency and they've only got so long to spend it before age catches up with them.
It turns out that running back and forth across a field for 90 minutes, while having to make sure you can still kick a ball in the right direction is pretty damn difficult. It's made all the more so when there's 11 people trying to stop you, and in some cases, hurt you quite badly.
At the top level of football - the age at which most professionals call it a day - is somewhere between 34 and 36, though their best years tend to have been and gone by then.
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For some players the end involves stepping off the stage at the end of the season and maybe getting some sort of punditry gig or podcast. At other points it's Gary Neville sitting in the toilets at half time against West Brom during a mid-season game realising it's the end.
One player who has lasted longer than most is Cristiano Ronaldo, still doing his thing on the pitch as he turns 40 today (5 February).
Something about Ronaldo's game that's helped him maintain his longevity is how he's adapted to the pressures of time and age, often by defying them, but how has he managed this?
Back in 2018, Men's Health reported that the then 33-year-old Ronaldo had a biology comparable to that of a 23-year-old, which might help explain why he was still going strong for Real Madrid at the time.
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When the man himself was 23, he was plying his trade for Manchester United in a season where he won the Premier League, Champions League and a whole host of individual accolades for his goalscoring, including the Ballon d'Or and FIFA World Player of the year.
The intense training regime
Ronaldo's insane fitness regime is clear to see as he whips his shirt off often enough in his goal celebrations to flex the results, while he's noted for taking 'care of his body as if it were a Ferrari'.
He exercises for up to four hours a day and makes five trips to the gym each week to work on his cardio and strength with the sort of workouts that would put Batman to shame.
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His workouts also involve Pilates and swimming to make sure that his body is the finely tuned instrument it looks like.
Maybe he's born with it
Apparently, part of Ronaldo's anti-aging regime is due to his genetics, with a lot of top athletes simply having some natural advantages (see also: the swimmer Michael Phelps).
Even if you lived like Ronaldo, there's no guarantee you'd be quite the athlete he is - you have to play with the cards mum and dad dealt you when you were born.
The planned diet
While most of us aim to get three square meals a day, Ronaldo instead prefers to have six smaller meals with less time between munching.
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Those long workouts need the right fuel, after all, and he needs to make sure he's eating the right things so his body has enough of the good stuff and avoids the worst things.
He's rather pointedly not a fan of sugary drinks, and like many athletes his meals are packed full of lean greens and proteins.
Ronaldo has said: "A good workout must be combined with a good diet.
"I eat a high protein diet, with lots of wholegrain carbs, fruit and vegetables, and avoid sugary foods."
His favourite food is Bacalhau à Brás, a Portuguese dish made of shreds of salted cod, onions, thinly sliced fried potatoes, and bound together with egg.
The sleeping habits
You'd think getting a good eight hours of sleep would be key to keeping your body as healthy as possible, and normally it is, but Ronaldo has five sessions per day where he's napping for 90 minutes.
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All in all, he's still getting seven-and-a-half hours and whatever he's doing is working for him, though given his lengthy workouts and regular mealtimes fitting in the sleeping sessions sounds like he's got a strict timetable.
This technique is known as 'polyphasic sleep' and it's done alright for him, though you try fitting it round your nine to five and see how that works.
Ice baths
Starting the day at 5am with an ice bath sounds like Ronaldo's way of doing things, or he'll go for a dip at 3am if he's had a match the previous day.
Recovery is all part of the regime and Ronaldo training incredibly hard and making sure his diet and schedule is scientifically perfected to get the best body would be pointless if all it did was wear him out.
"He's always training, with the team or at home," Santiago Segurola told Bleacher Report of Ronaldo's focus on getting the most out of his body.
However, despite managing to reverse his biological age to an incredible degree, time catches up with everyone in the end.
Ronaldo just turned 40 today (5 February) and is currently plying his trade in Saudi Arabia with Al Nassr.
Topics: Cristiano Ronaldo, Football, Sport, Health, Food And Drink
Joe Harker