Stretch to achieve a good position in an "earth touch"

Question

I had really tight hamstrings. I have been stretching them for quite some time now and it improved remarkably.

When I look at this picture I notice the straight upper an lower back.

This is not a picture of me, but I look basically like this (except for being able to almost touch the ground with the palms of my hands).

Now you will say, do the earth touch more, but there is a problem with it.

I can clearly feel that I compensate lacking flexibility with spine rounding. I feel, that if I only do the earth touch only my spine gets rounder over time.

So, is this still a hamstring problem or is it another muscle? Please give me specific stretch to achieve the position shown in the first picture.

Edit: Removed air squat part, because the focus should be first on the given stretch otherwise this thread gets to complicated in my opinion. I have a concrete problem at hand and I want to solve only this first.

Answer 1

The usual reason for butt wink is insufficient flexibility in external or internal rotation of the femur.

You have to create a 'groove' for your hips to sit into by pushing your knees out and pressing your hips forward, both by engaging glutes. Unfortunately it's more complex than that because at >90 degrees flexion some external rotators switch to internal rotation, but basically stronger glutes, looser adductors and hip flexors = no buttwink

Stuart McGill - Hip Anatomy http://youtu.be/IxAVJkbTf0M

There are so many factors in being able to perform a A2G squat with no buttwink and weight both on the bar and on your waist can be a factor as well as hip and ankle flexibility.

Here is another god article which may help: http://breakingmuscle.com/learn/6-mobility-exercises-for-an-a-to-grass-squat

On reddit and other sites there are places you can post a video to get help from total strangers on form. This may help as well.