Anuj, great post.
Kane what you are talking about is an exercise being recommended to people who are not ready at all for it. Now some machines are different than others and ghetto GHR's are VERY tough so I wouldn't suggest that as a test. But you make a very valid point about someone not being able to control the negative enough not to hyperextend his knees.
But this is how I teach the exercise. I advocate that people have something to catch themselves with. That's right, their hands. Probably a reason not to use machines sometimes. As far as assistance, bro, not many people can do a real unassisted GHR right off the bat. Most will have to assist themselves just to get going to some level or just enough to get past that sticking point so I was saying the same thing...a little assistance to assist but not perform the entire exercise, lol. Annd then control and perhaps accentuate the negative. I'm talking big strong guys. It is really difficult I admit and I would not every advice that a beginner do them without a catch. And I wasn't really advising that beginners do them anyway.
I was just exxagerating a bit to make a point about a huge big deal being made out of GHR's when really a lot of people aren't ready for heavy deadlfits but are able to pull heavy. There is a big difference between something like deadlifts and GHR's in that regard. If you aren't ready to do a GHR the exercise will let you know right away. Hopefully you won't hyperextend you knees finding out but you see what I mean. You'll find out, for instance if your lack the core control completely, or your glutes are too weak, etc...
Yet we are going to make a big deal out of GHR's, with built in feedback while we recommend deadlifts to everybody who comes along? Now most know that I am a deadlift addict, fanatic, and whatever else you want to call it but deadlifts do NOT have the built in feedback of a simple movement like GHR's. Less complex means more instant feedback. More complex means less.
I see people all the time who deadlift PAST their bodyweight right off the bat. Right off the bat. And I can tell you that they probably aren't ready to deadlift say, 10 to 20 percent past their bodyweight and yet they will be exceeding that in no time...yet you may have a person who doesn't have the core control to support his own torso in a GHR or can hardly do a plank.
And even when people start off moderately light you put them on this aggresive loading, every other week they are deadlifting TWICE and their apparent strength can quickly and easily outstrip their actual strength. And what I mean by that is that they are already skating on the edge of what they can do safely and things are only getting worse, not better, owing to all the bad baggage building up we've been talking about.
Deadlift being just an example of course.
So why am I going to worry about GHR's? Although I see your points completely and they are valid. You can get hurt doing anything. The problem is the things that HURT US AND WE DON'T EVEN KOW IT. Are you catching my drift?
I mean I've seen people go on and on about how you should cheat on curls
. After a while it becomes people just talking about form just because they've heard the word mentioned once or twice. You can get hurt doing any exercise with catastrophic failure like you spoke about. But MOST of the injuries don't come all at once, right? They are the hidden thing waiting to pounce. But yeah, if peope can't evne control the negative at all....probably need to start with some very basic strengthening but I would advise peope have some way to catch themselves. But what I don't understand is why did they hyperextend their knees instead of just letting their hips flex forward to decellerate? It seems more a problem of a person really just needing some coaching you know? I certainly don't advize things I'm not willing to teach people how to do, give them some things to expect, etc..