Hey Arnold wrote:
The strain is high up near or maybe at the hip flexor it feels like.
At the hip flexor, no, it is the hip flexor. One of them.
The only part of the quad that can go past its range of motion is the rectus abdominis. It's a bi-articulate muscle that crosses both the knee and hip joints, giving it two functions which it usually doesn't perform at the same time.
Figure out how it's impaired, knee extension or hip flexion, that will point the way to rehabbing it. If it's impaired hip flexion, knee extensions will be irrelevant.
The three vastus muscles can't be hyperextended because they only cross the knee joint and the tibia can't be flexed past the femur. But they can still form trigger points, particularly on the v. lateralis.