Rectus Femoris

The Rectus femoris muscle is one of the four quadriceps muscles of the human body. All four combine to form the quadriceps tendon, which inserts into the patella and continues as the patellar ligament.

The Rectus femoris is situated in the middle of the front of the thigh. It has a spindle-like shape that is wide in the middle and tapers at both ends, and its superficial fibers are arranged in a bipenniform manner, the deep fibers running straight down to the deep aponeurosis.

Functions of the Rectus Femoris

The rectus femoris has two main functions:

Hip Flexion - The rectus femoris is a weaker hip flexor when the knee is extended because it is already shortened and thus suffers from active insufficiency. In essence: the action of raising a straightened leg will recruit more iliacus, psoas major, tensor fasciae latae, and the remaining hip flexors than it will the rectus femoris.

Knee Extension - the rectus femoris is not dominant in knee extension when the hip is flexed since it is already shortened and thus suffers from active insufficiency. In essence: the action of extending a leg from a seated position is primarily driven by the vastus lateralis, vastus medialis, and vastus intermedius, and less by the rectus femoris.

The hamstrings oppose the rectus femoris at the hip joint through extension and at the knee joint through flexion. It is important to keep the rectus femoris as when it is torn it can be very painful.

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