In the bird dog exercise, avoid raising the leg too high to prevent arching the lower back.

“a key point is to make sure you don't raise the leg too high you're not trying to Arch your lower back in fact what you want to do is raise the hand in front of you generate that fist it can even just be out in front of your your eyes at first maybe a little bit higher and then the leg that's extending toward the back feel free to either point the toe toward the ground or if you want to extend the toe a little bit like you're doing a little bit of calf raise in the air right pointing your toe that is that's fine too but don't get that heel up too high or even the upper thigh up too high that you're getting a really big arch in the back”

“so you get into all fours on the ground you extend one arm forward and you extend the opposite one leg backward okay so if you're down on all fours and you extend your right hand in front of you you're going to extend your left leg behind you”