Quads are a big muscle group that is often below our radar. We use them every day every time we walk even a few steps, but since it does not often cause direct pain, we can overlook the way it can contribute to problems in other areas.
One of these “other areas” would be the lumbar spine. The upper fascial layers of the quads extend into the hip flexors deep in the anterior lumbar spine. The hip flexors and the muscles in particular bear much of the blame for causing anterior lumbar spine shifting and secondary compression/extension of the lower lumbar discs, but the quads can do the same thing. The diagram does a fairly good job at depicting the shift in the lumbar posture. Incidentally, this also causes some overload lengthening of the hamstrings and could be a silent source of constant straining of the posterior thigh.
Heavy use of the quads during certain type of occupations (construction workers, laborers etc…), with little rest in between, seems to be a common trigger for chronic myofascial shortening of the quads (whereas muscle shortening is more often triggered by prolonged sitting). You can pick up on the problem when placing the patient in a stomach lying position and bending both knees to 90’. With normal quads flexibility you should be able to achieve that without causing recruitment of lumbar extension or lateral shifting of the glutes. In patients with short quads, you will start noticing some strong resistance, lumbar extension and side gliding of the thigh as early as 45’.
For patients with very short quads, traditional stretching may not be the place to start since you can further aggravate lumbar extension in the process. You may need to start with more passive lengthening therapies and adhesion break up using a foam roller in the prone position for the entire length of the muscles.