How to stretch hamstrings w/out over extending the knees?

[MeltingSnowflake]

Just that really - I've just taken up yoga, partially to stretch out my hamstrings, which are horribly tight from sitting at a desk all day.

But I find that in many of the poses I get pressure in the back of my knee from over extending. But if I slightly bend my knees, I'm not stretching my hamstrings.

I'm trying to tense my quads, but I think I might just be tensing my hip flexors (which are also tight). Any ideas?

Thanks in advance!

I have right hamstrings. Acro yoga teacher has shown me an exercise with a resistance band to help - basically lying down, foot in band, leg bent, grip band with both hands then stretch leg out. You can do it with a towel/sock if you don't have a band.

You shouldn't be tensing anything. Tense is the wrong action.

Your thighs - especially quads - need to lift, that is to extend towards your hips. Your calves have to extend towards your heels. Your quads and shins should move back (if standing, down if sitting) but the back of your knee should not. Your knee cap should lift, towards your quads (but not lift up out of your leg). At no point should the words "tense", "clenched", or "hard" feel appropriate. ("Lifting", "lengthening", "gripping" are all good).

Standing with toes higher than heels will help to get the length. Slowly over time, not overnight...

Thanks for the feedback!

I'm not sure of the difference in feel between tensing my quads and lifting them though. Maybe I need to get myself to a class and get some one on one tuition!

If you anteriorly tilt your pelvis (direction of sticking your bum out) you can stretch hamstrings with a slight bend in the knee.
You can do this effectively in downward dog or variations of this move e.g. leaning forward onto table with slight bend at knee and then tilt pelvis until you feel hamstring stretch