Oh Psoas, Where Art Thou?

Run much?
Squat much?

You may want to pay attention.

You need symmetrical psoas muscle activity to pull you down into a symmetrical squat. 
You also need your psoas during the swing phase of running to possibly reduce impact forces and loading rate (Schmitz et al, 2014).

What's wrong with this front squat position?

Did you notice my right knee is lower than the left? I've rested elbows on my knees, holding a dowel, to indicate the drop on the right side. 

That's my natural position - for some reason, I don't flex my right hip the same as my left when I deep squat. 

I've elevated heels to remove any ankle involvement in the pattern. 

As it goes, I can actively adjust to line the hips up in this position, but it's not a natural position and I definitely don't maintain it. 

When I squat under load, or deadlift, or pistol squat, I have a sensation of discomfort in the right lower back - same side as the hip that isn't flexing as much as the other side.

​What do you think could be the reason? 

• I have pain at that range of hip flexion;
• The hip can't flex enough - it doesn't have enough mobility; or
• The hip can flex - has enough mobility - but I have poor control in the inner range of hip flexion.

I don't have pain. 

Let's look at 2nd one - can I get as much flexion as the other side, passively? This video shows that I can. 

Now watch what happens when I use "core activation" to assist active hip flexion. 

That core activating will improve psoas activity gives me a corrective exercise. 

To progress that, I resist the pattern of hip flexion, such as I did with this track sprinter in China. 

Then I add core-assisted squatting, such as I did with this handball athlete from China. 

Reference:

SCHMITZ, A., POHL, M. B., WOODS, K. & NOEHREN, B. 2014. Variables during swing associated with decreased impact peak and loading rate in running. J Biomech, 47, 32-8.