question: how high is that box you made, and how tall are you?
I woulda made it deeper so that you have the option to sit back further.....that way you can basically walk yourself right to the edge of the box and not have to worry about overshooting the box.
the thing I use at the gym has a nice large square surface...it's constructed out of metal though....the one I use is about 18" high i'd guess...which may be a little too high for me.
anyway, I can certainly see you are rounding your back on the box squats.....
the other vid, all that is in view is your legs, so it's kind of hard to tell what the rest of you is doing. but, it does look like your knees are coming way out over your toes - which is not good. you can prevent that by doing box squats far back on the box. watch - your box squat again, your knees are where they should be.
you might need some more flexibility in your calves and hamstrings to be able to do regular back squats correctly.
I woulda made it deeper so that you have the option to sit back further.....that way you can basically walk yourself right to the edge of the box and not have to worry about overshooting the box.
the thing I use at the gym has a nice large square surface...it's constructed out of metal though....the one I use is about 18" high i'd guess...which may be a little too high for me.
anyway, I can certainly see you are rounding your back on the box squats.....
the other vid, all that is in view is your legs, so it's kind of hard to tell what the rest of you is doing. but, it does look like your knees are coming way out over your toes - which is not good. you can prevent that by doing box squats far back on the box. watch - your box squat again, your knees are where they should be.
you might need some more flexibility in your calves and hamstrings to be able to do regular back squats correctly.