2) Did this go out of style and come back? I remember hearing about the benefits of "isometric overload" like this the whole way back in the late 1980s.
For a long time physical therapists wouldn't recommend knee extensions for ACL reconstruction rehab due to forces through the graft, but that has changed recently. My PT recommends them to me.
Read this: https://theprehabguys.com/is-the-knee-extension-machine-safe...
TLDR: 1.Squats place a similar force through your knee, except the force peaks when your knee is bent rather than when it's straight (as in leg extensions)
2.Leg extensions are the only reliable way to rebuild quad strength post surgery, and quad strength is by far the strongest predictor of reinjury to the ACL.
I believe my lack of quad-specific training contributed to my initial injury. I did tons of squats and deads and my hamstrings/glutes were strong, but I think my quads were behind. I had trouble slowing down from a sprint during soccer/walking down stairs prior to my injury, and I think those were warning signs