I’ve been trying to drill clams for both hips with deep belly breathing, but have that some muscle on the front of my thigh is highly active throughout the whole motion and takes away my ability to feel it deep in the hip. It looks like a tendon stretching from my ileum into the VMO, but not sure what it is, maybe Sartorius or…? Is the anterior thigh supposed to be active as an ER?
I would expect this muscle to be the RF or Satorius. These are likely culprits as they typically shift to tonic in the presence of pain and severe dysfunction.
I typically see them limiting sagittal plane motion, not transverse, but it is very reasonable that this tone would create some inhbition in the glutes.
I would look for tender points through that muscle or see if you can destroy the whole line of what you see with Gua Sha or Graston.
Also keep in mind that the Clamshell must be performed with neck support to neutral and sidelying completely in the frontal plane. There are also some arm positions that can be coached that are a part of the Reflexive Turning 3 position in Reflexive Stimulation of DNS.