The vastus intermedius, one of the quadriceps muscles, lies deep within the thigh, contributing to knee extension.

Origin:
Arising from the anterior and lateral surfaces of the femur, the vastus intermedius has its origin along the shaft of the femur.

Insertion:
The muscle inserts into the quadriceps tendon, which then merges with the patellar ligament, attaching to the patella and tibia.

Function:
The primary function of the vastus intermedius is knee extension, working in conjunction with other quadriceps muscles to straighten the leg. This action is crucial for activities like standing up from a seated position, walking, running, and jumping. The vastus intermedius plays a vital role in providing stability to the knee joint and supporting lower limb movements.

Knee Extension (Leg Extension)

Squat

Machine Squat

Lunge

Side Lunge

Leg Press