I assume he means:
Closed guard -> Stacking -> Neck problems. Rubber guard -> cranking on your own knees -> knee/hip problems.
Its a sport. Basketball, running, cycling, tennis, hell even golf has injuries.
Being active regularly = injuries.
Most (not all) injuries are avoidable. In my experience, people get hurt more early on. My coach says people get hurt less at higher ranks because by then "they've been around the circus for a while and they've seen all the clowns". Most of my injuries these days come as punishments for having too much ego rather than inexplicable catastrophe: "I WILL finish this takedown" "This lower belt won't sweep me!" "That toehold isn't that tight".
why does closed guard - rubber guard lead to injury
I've been injured in bjj. I recently had a radial break in my wrist area. Had to be casted and stay off the mats for 3 months. It still hurts. I've sprained my ankles, hurt my knee, my shoulders are all fucked up, and I think I'm starting to get arthritis in my fingers.
As Kesting says, it's inevitable in a contact sport. I'm 43 now. I don't recover as fast as I did even 10 years ago.
There is a 59 year old man that trains with us. He played hockey his youth and into university. He is one tough dude. You need to be careful who you are training with. I no longer seek out the young wrestler who jut graduated from college or the young kid who thinks he has something to prove by tapping a purple belt. Sure I can turn it up but there are more seasoned guys I like to train with.So, I'm of similar age... I have not done any BJJ like you, but I'd like to. In my time, it is all from traditional sports like basketball and football. I've got bad knees, bad neck, bad back, bad shoulders, messed up finger. Other than that, I'm OK!
Seriously though, to look at me, I'm an athletic and fit "young man". (That's what people think I am.) My wish (in taking up BJJ) is to find something that will "keep my young" (i.e. keep limber, flexible). I know I've heard how bad BJJ is for your spine, which is the death of limberness and flexibility. But I wonder if I can readily manage my fragile body as I get into BJJ.
Cuz really, I can't afford to be hurt all the damn time.
Regular closed guard doesn't lead to injury.
In the rubber guard there is a lot of temptation to bend your own leg in a wrong way to accomplish something.