There are many times when you feel tensed or tired and your joints ressist. In case you are squatting down and you want to avoid bending forward (with a backpack on you or an injured friend) Simply slide one feet as you go down and this funnels the tension so you can keep the alignment. Try this in movement by throwing something light to the ground and squat to pick it up as you keep moving and repeat a few times. It is a good way to learn to move well and you can do this with a partner as a response to a strong push. Using this you can both stay close to the pusher and escape his hands which can be the thing to do in knife or gun cases. Decide for yourself when it will work for you and remember to keep thinking and moving as you work with different partners.
Another note is to work with different people. You can learn something from everyone.