if you have been known to be super bendy in your knees and elbow joints (read: when you straighten these joints it looks like they start to bend the other way), then you could be prone to injury in yoga. but yoga can also be the cure!
basically, when you hyperextend, you hang out in your joints, so instead of your muscles holding you in place, you are putting the weight and stress on your joints which are held together by ligaments and tendons. ligaments connect bones to bones and tendons connect muscle to bones, making them critical to creating a stable joint. however, unlike the stretchiness of muscle tissue, ligaments and tendons are less stretchy and if you stretch them too much (which you can do via hyperextension) they may not bounce back, thus weakening your joint stabilty which could lead to injury. and so when you in poses where you are in full extension, try to give a little microbend in your joints, you'll be surprised to know you are still in full extension without putting any unnecessary stress on your joints.
et voila! by microbending, you'll not only activate your muscles, building strength, but you will protect yourself at the same time. how's that for multi-tasking?
common poses to be aware of hyperextension include: plank (elbows), upward facing dog (elbows), triangle (knees), all forward folds (knees).