What's the muscle

moneymad

While sitting down, lift up your right leg and rest your ankle just above the knee of your left leg.

Lower the right knee towards the floor. What's stopping the knee going parallel to the floor?

AllForIt

The same thing that's stopping you from scratching you nuts with your toes.

Triceratops Ballet

The periformis?

Mellor

Internal rotation in the glutes. Could also simply be hip structure

Testosterscone

moneymad wrote: »

While sitting down, lift up your right leg and rest your ankle just above the knee of your left leg.

Lower the right knee towards the floor. What's stopping the knee going parallel to the floor?

Sounds like you are describing the sartorius?

Alf Veedersane

There's likely no single answer. The restriction I feel is different between left and right.

There are a lot of moving parts involved

Mellor

Testosterscone wrote: »

Sounds like you are describing the sartorius?

Sartorius would be the opposite action to what he describes

calfmuscle

Piriformis tightness will keep you from reaching parallel, but the family of hip external rotators will all be involved as well.