What is the Vastus Intermedius?
The vastus intermedius is one of the four muscles that make up your quadriceps, the big muscle group on the front of your thigh. It sits deep in the middle of your thigh, underneath two more visible quad muscles, so you usually cannot see or feel it as clearly from the surface. It starts on the front and outer portion of your thigh bone (the femur) and runs down to attach into the quadriceps tendon, which connects to your kneecap. From there, force is transferred through the patellar tendon to your shin bone, letting you straighten your knee.