One of the 5 main muscles of movement.
Keeping it simple: rectus femoris
The rectus femoris muscles run down the front of each thigh, from pelvis to tibia (hip bone to shin bone).
rectus ≅ straight
femoris ≅ femur
Rectus femoris keeping it simple.
Described as part of the quadriceps femoris muscle group, along with the 3 "vasti" muscles (the vastus lateralis, vastus intermedius and vastus medialis). The distal (end furthest from the center of the body) tendons of these 4 muscles merge to form the common quadriceps tendon, which attaches to the patella (kneecap) and then continues as the patellar ligament to the tibial tuberosity of the tibia.
The rectus femoris attaches to the pelvis, whilst the 3 vasti muscles attach to the top of the femur (thigh bone).
When fully engaged along their full length, the rectus femoris muscles correctly align the knee and hip joints, positioning each leg so that the other thigh muscles can work as they should.
The pelvic attachments of the rectus femoris muscles are commonly described as "to the ilium of the pelvis via two heads - the straight head and the reflected head" but it is not that simple - variations in the pelvic attachments have been observed.
Anatomy - A Few More details.
The heads of the rectus femoris merge into an aponeurosis (thin sheet of strong connective tissue), from which the muscle fibres arise as the aponeurosis continues distally (away from the center of the body) on the anterior (front) surface of the muscle.
The lower two-thirds of the posterior (back) surface of the rectus femoris consists of a thick, broad aponeurosis that becomes narrowed into a flattened tendon attached to the patella. This forms the superficial, central part of the common quadriceps tendon.
Movement should not be painful.
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