While I was teaching the daughter of my student Lisa yesterday, Lisa came in to tell her daughter that the very best thing she learned from me in yoga class: to lift her kneecaps up.
She said that in yoga class she could do anything if she lifted her kneecaps up. I was impressed, and inspired myself, since I am a classic accidental knee-locker. A lot of knee-lockers (ahh!, You didn't know there was a club!), don't really know how to lift the kneecaps. This is not good at all because locking puts too much pressure on the knees, and stops the flow of energy, or prana through your legs.
Besides, Mr Iyengar (in my opinion the god of yogic alignment) is a big fan of lifting the kneecaps up, and I go with him on issues like this.
Here is a short exercise that you can try to experience your knee lifting capabilities:
Stand on your two feet and bend your knees as if you were going to sit back onto a chair. Place your hands on the muscles of your thighs. Slowly start to straighten your legs and as you do, root your feet into the floor, and use your hands to encourage your thigh muscles (quadriceps) to lift up. Try not to push your legs back in space (locking them), but lift them up toward the sky. Squeeze them up like this for 5 breaths, and then release, and just notice how you and your legs feel. Stand in your Tadasana (mountain) pose.
Now you can do anything!