I work out in an university gym so i see all types. Some day i'm going to film this older (i guess early 60s) guy that comes in there. He wears the best athletic clothes one can buy, those boise headsets, and a hat (I guess he's bald). That guy squatting does 5X more range of motion than this guy does. Most of the time you can't even tell he's moving. Just a VERY slight bouncing. I was doing bent over rows and noticed in the mirror he was on the decline bench apparently doing situps, i watched him for a minute because it seriously looked like he was stuck, not moving or anything, but then i realized those slight head nods counts as reps for him. The most range of motion i've ever seen him do (he's in there about 2-3X a week), was on the machine flyes. He brought the handles all the way out in front until they touched, i was amazed, but then noticed him moving the handles about half an inch apart from each other and bringing them back together for reps.
Some day i'm going to tell him "WHOA WHOA WHOA THERE MAN!!!! keep the range of motion short to keep the stimulas on the muscle! keep going as far as you have been and you'll develop joint problems"