Dented Iron

What happens when you get enough injuries, even if you appear to be Made of Iron.

Punch-drunk boxers are the classic real-life example of what happens to someone who takes repeated pummeling damage in many fights year after year. However, the American National Football League is a better sampling. To survive more than a couple of seasons in the league is a guarantee of a lifetime of painful, lingering damage to battered joints, bones, and connective tissues. That life is also going to be about ten years shorter than that of the average adult American. The heart and body organs build up scar tissue likely to fail when the athlete is in his fifties and sixties.

Will result in Crack! Oh, My Back! as the person ages. If someone fits this but insists they're Made of Iron, that person is a Perilous Old Fool.

Examples of Dented Iron include:

Anime and Manga

One Piece: Whitebeard is covered with scars on every part of his body except his back, the only wound there being from a sword he was impaled with from the front; this is proof that he was such a badass that he never fled from a fight, ever.
This is the primary reason the original heroes of Kinnikuman, especially Kinnikuman himself, had to step aside for the younger generation in Kinnikuman Nisei.
This trope is brought up in the third and final arc of Rurouni Kenshin. In the epilogue that takes place five years later, it's gotten so bad that Kenshin has to give up swordsmanship, despite only being in his 30s, because his frame was lighter than what his style was designed for.
Invoked during the course of the Blame manga with the main protagonist, Killy, who endures many physical hardships during his journey. By the final chapters, his otherwise indestructible body is literally falling apart.

Comic Books

Batman whenever they show him in old age (The Dark Knight Returns, Batman Beyond, Kingdom Come, etc.)

Film

Requiem for a Heavyweight
Rocky V
- Really a theme present in all Rocky films.
The Wrestler
Death to Smoochy: Spinner Dunne

Literature

Evoked in one Redwall book with Lord Asheye, a Badger Lord who fought a great deal when he was younger and is now always aching because of his many, many scars.
Very much a running theme in The Acts of Caine series with Hari/Caine
Lampshaded and averted in The Dresden Files, where Harry notes that the amount of punishment he's taken over the years would give him the health problems of a football player. But, as a wizard he heals perfectly over time, without scar tissue or the aftereffects of broken bones.

Live-Action TV

Whenever a Police Procedural does an episode involving contact sports, there's a good chance that this trope will arise, probably because someone is covering up the fact that a celebrity player is dented iron and shouldn't be competing at all.

Music

Paul Simon's "The Boxer".

In the clearing stands a boxer and a fighter by his trade,
And he carries the reminders of every glove that laid him down,
Or cut him 'til he cried out in his anger and his shame,
"I am leaving, I am leaving."
But the fighter still remains.

Similarly, John Gorka's "Dream Street."

They never leave the ring before it's too late
They never seem to quit in their prime
I guess it's taken as a given that a champion is driven
So he can always win one more fight.

Professional Wrestling

One heartbreaking real-life versions of this was the case of pro-wrestler Chris Benoit. After his death, studies showed that his brain was comparable to that of an 85-year-old Alzheimer's patient (he was 40 at the time.)
The Undertaker is the same way.

Video Games

In the first Baldur's Gate, Dynaheir implies that her bodyguard Minsc's 'unique' view on life is the result of taking too many blows to the head over his career as a berserker.
Geralt from The Witcher. By the time of the second game, he's covered with scars. This is not an unusual feature on Witchers, as other games in the franchise prove.

Web Comics

Ben T. Sharpley from Everyday Heroes was caught in a training accident while in the Army. Because of this, his spine is bent at a right angle; still, he manages to work full-time running an amusement arcade.

Real Life

Several of the rules in Mixed Martial Arts seem to have the intended effect of mitigating this—for example, the lack of a standing count in MMA as well as referee stoppages (a referee is to stop a fight where a fighter is incapable of or is not "intelligently defending" himself or herself), as well as mandatory medical suspensions (in North American states where the sport is sanctioned). However, as the sport is so young there's only a few fighters who are anywhere near old enough to show this effect... although some of those from the "Dark Ages" of MMA, such as Gary Goodridge, have shown this trope to a disturbing effect.