Burpee/Squat Thrust Form question

[elsie3]

Thank you for your amazing workouts.

I have a question about form on Burpee's or Squat Thrusts, especially with the disks. When I jump (or glide) back in, my knees naturally splay out to the side--froggie-style. I find this more comfortable, but I always thought perhaps I was "cheating" the move and not getting the full benefit. The last time I was doing a LIC workout and really concentrated on keeping my knees forward, I really felt it in my lower back later--not in a good way. So I'm wondering if I should just go with my inner froggie, or if I need to correct my form to knees forward and build up more endurance (or something) in my lower back. As a side-note, I've never had lower back issues with any other exercise--weights or cardio.

Thanks,

[nsaeolian]

I hurt my lower back this week doing these too. Any hints as to what I might be doing to cause this?