Middle split questions

Hello,

I've got some questions about the exercises in the middle split series. 

Starting with the piriformis, why do we start in straddle? Then, when we're in position, do we need to lower the working knee or the glutes? Does the foot of the working leg needs to be in line with the other leg or the center body?

For diamond frog, what's the point of pushing the feet down?  Is it to strengthen the adductors?  Do we need to progressively move the knees toward us?

For the frog and straddle positions, can I pull myself with the help of stall bars, for exemple, to get my back flat?

Why all those straddle variations (walk, bounce, slide...?)

In the isometric middle split, what is too low? When the glutes come out of the line?

Finally, in the last middle split exercise, is it important to extend our arms while lying?

Thank you very much!

HI Etiènne, here follows the answers:

-begin in the straddle position with external rotation of the working leg it is a good way to maintain the external rotation. but there is not a preference here

-the foot must be aligned with both knee and center of the body, the ability to more the butt to the floor it is limited by the psoas of the posterior leg, the idea it is to reach the floor with the knee and the upper leg.

-when adductor are tight there is a strong internal rotation which leads to the feet to comes up from the floor.

-instead of use something else, try to do that actively. it makes a huge difference.

-too low it is the point where you cannot hold the position, simply be conservative.

Thank you for your answers!

But I am still curious, what are the big differences (in the working process) between every variations in the straddle position?   

And, in the videos for the pancake roll through, they extend their arms while lying on the ground, is their a specific purpose? 

Thanks again!