<P> In addition, recent cadaver studies have confirmed the presence of a sixth muscle, the tensor vastus intermedius . While the muscle has variable presentations, it consistently originates at the proximal femur, runs between the vastus lateralis and vastus intermedius muscles, and inserts distally at the medial aspect of the patellar base . Historically considered a part of the vastus lateralis, the tensor vastus intermedius muscle is innervated by an independent branch of the femoral nerve and its tendinous belly can be separated from the vasti lateralis and intermedius muscles in most cases . </P> <P> Femoral nerve (L2, L3, L4). </P> <P> All four quadriceps are powerful extensors of the knee joint . They are crucial in walking, running, jumping and squatting . Because rectus femoris attaches to the ilium, it is also a flexor of the hip . This action is also crucial to walking or running as it swings the leg forward into the ensuing step . The quadriceps, specifically the vastus medialis, play the important role of stabilizing the patella and the knee joint during gait . </P> <P> In strength training, the quadriceps are trained by several leg exercises . Effective exercises include the squat and leg press . The isolation movement (i.e. targets solely the quadriceps) is the leg extension exercise . </P>

What is the principle action of the vastus lateralis and the other quadriceps muscles