Vastus lateralis
The largest of the four quadriceps, forming the outer sweep of the thigh.
- Type
- Muscle
- Region
- Thigh
- Standard name
- m. vastus lateralis
- Origin
- Greater trochanter, the intertrochanteric line and the lateral lip of the linea aspera of the femur
- Insertion
- Lateral border of the patella, then the tibial tuberosity via the patellar ligament
- Actions
- knee extension
- Verify
- TA2 2618 TA98 A04.7.02.021
What it is
The biggest head of the quadriceps and the one on the outside of the thigh, arising from the upper femur and the rough ridge running down the back of it, then sweeping down and forward to the outer edge of the patella.
It is the muscle that gives the outer thigh its shape, and it is superficial enough to be seen working in most people.
Because it is large and accessible, it is a common site for intramuscular injection in adults and, notably, the preferred site in infants.
What it does
Extends the knee. That is all it does — it arises on the femur and ends below the knee, so it crosses one joint.
Its pull on the patella has an outward component, which is balanced by vastus medialis pulling inward. That opposition is part of how the kneecap is kept tracking in its groove.
What loads it
Any loaded knee extension, and any controlled bend of the knee under load. Squats, lunges, step-ups, stairs, and cycling.
The goblet squat and box squat both load it through a substantial range.
What is commonly got wrong about it
"Sweep" as something you can train for. The outer curve of the thigh is largely a matter of how big this muscle is and where it attaches, and attachment points are not trainable. Training it makes it bigger and stronger; it does not redistribute it.
That it works against vastus medialis. They pull the patella in opposite directions, but they are not opponents — the opposition is the mechanism that centres the kneecap, and both firing together is the normal state.
Foot position changing which quadriceps head works. Turning the toes in or out during a leg press or squat is widely claimed to shift emphasis between the vasti. The evidence for a meaningful shift is thin, and the change in what your hip and knee are doing is far larger than any change in which head is working.