Were you referring to people like Andy Hug of Kyokushinkai?

I believe he suffered from an illness, but in general I suppose having a full-contact punching and kicking bouts with gigantic men isn't very good for your long-term health anyway. Especially in Kyokushin where they have (had?) no weight classes.

Yes. For example.

I actually don't think it is the direct damage from fighting that gets them but more the inability to stop and scale your commitment to what you can and can no longer do.

Direct damage from combat sports can catch up to you eventually. CTE is pretty serious, but unfortunately you probably don't realize the extent of that damage until it's far too late.

I know multiple martial arts practitioners who had to have hip surgery at a relatively young age. It’s really easy to overestimate what your body can handle.

Going from a black belt in Taekwondo (age 7-16) to doing Isshin-Ryū karate (with some BJJ, aikido, and budokai in between) was really eye-opening. Taekwondo is all about sharp form, clean lines, high kicks. Punches and kicks go to full extension, and the stances are fairly deep.

In Isshinryu, there's none of that. You stop the punch/kick before the joint goes to lock. The stances are much shallower. The movements are less dramatic. My sensei told me it is much more sustainable this way, and many of the old taekwondo folks end up with joint issues specifically in knees and elbows. I don't know if it's related, but my knees and elbows are the two parts of my body which are most problematic.

It's also possible my taekwondo instructor just didn't know about this, that was a long time ago.

> There were all these character who had seemingly superhuman physical fitness yet they would die really early. I always wondered why was that?

Performance enhancing drugs

Anything to an extreme is unhealthy, and making your whole personal identity any single thing - being an athlete or a pilot or a father or gay or disabled or a Christian or whatever - is a bad idea. But the statement "a lot of physical training isn't that healthy" is pretty objectively wrong.