I used to do leg extensions years ago. You can get a good burn in the quads. But it's not a "natural" movement, and I've since read that it's not so good for the knees.
I understand the resistance is on the end of foreleg as opposed to the bottom of the foot. Show me where this is bad?? It's unnatural, yes. bad, ??
Perhaps I chose the wrong word to describe it. Such an isolated movement has no evolutionary basis. Would you consider compounds like upright rows and behind-the-neck presses as "natural" since the body can do it? They also have no evolutionary basis and are considered to be rotator cuff assassins, at least in part because they require the elbows to be splayed too wide, potentially causing impingement.
Upright rows are power cleans with more control over the load and a lot lighter on the cuff? Are you saying early man never picked anything up off the ground to shoulder high?
I think I'll pass: https://www.google.com/search?q=upright rows bad&cad=h Again, no evolutionary relevance. Sorry to sound like a broken record, but I think the human body has evolved to suit the movements that preceded its latest configuration. You can go outside those movements if you wish. I choose not to do so (anymore).
I think the squat is unique in the sense that it's definitely the hardest and most intense exercise to do, and also because it seems... for whatever reason... to put size on a person like nothing else. If I want to put on 10lbs of muscle in a couple of months, all I need to do is focus on squatting heavy.
I don't know what this means. Movement is rotation about joints. Skill is compound movement across joints. Given, the leg extension loads the leg, the quads in a way that's not so much seen in nature. That doesn't mean it is harmful, that's to be proven. You haven't. The barbell doesn';t exist in nature either does it. Is it harmeful as a precise tool??