maybay wrote:My friend had to have surgery on his knees because he tried too hard with the lotus position.
Rgeally showcases why it shouldn't be forced. I have damaged my right knee because I spent years in the half lotus flexing at the knee when I should have been stretching my hip.
Ironically, though I can no longer sit in half lotus with my right foot up without feeling it in my knee for a day afterwards, I can sit full lotus without any such niggles.The weight and lock of both feet helps ensures the flex is at the hips, whereas in the half lotus, which is more loose, I can't stop my hyper-extended right knee from compensating. It took some training, stretching and opening up the hips though. And there is still a lot of hip flexibility ahead of me yet. I recently found out that full deep squat can be done with erect spine without curving the lower back.

I've got a new stretching regimen to get there.
I think a nice rule of thumb is that if you can't go into the lotus and relax all muscles without the posture falling apart, you're not limber enough yet. Having a relaxed posture also goes a long way towards stretching in the right places when you do sit.