Vastus Medialis

legsMusculus vastus medialis

The vastus medialis runs down the inside of the thigh and forms the teardrop-shaped bulge just above the knee. It extends the knee and helps keep the kneecap tracking straight.

Vastus Medialis highlighted on an anatomical figure, from the front.
Where it sits, from the front.

Vastus medialis arises along the inner side of the thigh bone and runs downward to the inner edge of the kneecap. Its lowest fibres approach the kneecap at a much steeper angle than the rest, almost horizontally, and it is this lowest portion that produces the visible teardrop above the inside of the knee.

Those oblique lower fibres are often given their own name — vastus medialis obliquus, or VMO — and treated as a separate muscle in training material. Whether they are genuinely a distinct subdivision, and whether they can be trained selectively, is a real and unsettled question. Anatomically they are continuous with the rest of the muscle and share its nerve supply; some studies find a distinguishable innervation pattern and fibre orientation, and others do not.

What the fibres do is not in dispute: they pull the kneecap inward, opposing the outward pull of the vastus lateralis, and that balance keeps the kneecap tracking in its groove as the knee straightens.

It also extends the knee like the other three, and like them it crosses only the knee, so its function is unaffected by hip position.

Training notes

Selective training of the teardrop is the most persistent myth in leg training, and the evidence does not support it. Terminal knee extensions, quarter squats, toes-out stances and adduction-loaded extensions have all been proposed; none has shown a reliable ability to recruit this part of the quadriceps preferentially.

What does develop it is the same thing that develops the rest: knee extension under load through a full range. The teardrop becomes visible when the quadriceps as a whole are well developed and body fat is low enough to show it.

Deep squats load it well, since the quadriceps contribute most at the bottom of the range and nothing about that position disadvantages this muscle.

Because it sits low on the thigh and close to the surface, it is one of the more visible parts of a developed leg — which is why so much attention attaches to it.

Anatomy

Origin
  • Intertrochanteric line, the spiral line, and the medial lip of the linea aspera of the femur
Insertion
  • Medial border of the patella, through the quadriceps tendon
Actions
  • Extends the knee
  • Draws the patella medially, balancing the outward pull of the vastus lateralis
Innervation
Femoral nerve (L2–L4)

Exercises

Antagonists

Synergists