I'm recovering from ACL reconstruction, so I'm not up to doing everything I used to do.
But, when healthy, I do seated leg press as a core workout. Not a cable machine, but the kind you load with 45 pound plates. This spares my back, and I can load a lot of weight on there if I'm in the mood. Squats are out for me.
I do seated leg extensions (and hamstring curls to offset them), and these have to be the most hideously painful exercise I've ever done. The burn always...ALWAYS comes after I finish the set. Never during...after. It kills me. Its like somebody has injected carbolic acid into my thighs. Its all I can do to keep from losing my composure. I hate it, I love it.
I've found, though, that the leg press is enough for the most part. The other stuff is extra. If I do it all in one day, it fatigues me beyond reason.
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Shesulsa...you might check with your physical therapist before doing those Hindu Squats. It looks like that really loads the knee.
Regards,
Steve