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The rectus femoris biarticular muscle acting over the hip has a smaller hip moment arm than the hamstrings. However, the rectus femoris moment arm is greater over the knee than the hamstring knee moment. This means that contraction from both rectus femoris and hamstrings will result in hip and knee extension.
The three 'true' hamstrings cross both the hip and the knee joint and are therefore involved in knee flexion and hip extension. The short head of the biceps femoris crosses only one joint (knee) and is therefore not involved in hip extension. With its divergent origin and innervation, it is sometimes excluded from the 'hamstring ...
The semimembranosus muscle (/ ˌ s ɛ m i ˌ m ɛ m b r ə ˈ n oʊ s ə s /) is the most medial of the three hamstring muscles in the thigh. It is so named because it has a flat tendon of origin. It lies posteromedially in the thigh, deep to the semitendinosus muscle. It extends the hip joint and flexes the knee joint.
The biceps femoris (/ ˈ b aɪ s ɛ p s ˈ f ɛ m ər ɪ s /) is a muscle of the thigh located to the posterior, or back. As its name implies, it consists of two heads; the long head is considered part of the hamstring muscle group, while the short head is sometimes excluded from this characterization, as it only causes knee flexion (but not hip extension) [1] and is activated by a separate ...
The hamstrings are innervated by the sciatic nerve, specifically by a main branch of it: the tibial nerve. (The short head of the biceps femoris is innervated by the common fibular nerve). The sciatic nerve runs along the longitudinal axis of the compartment, giving the cited terminal branches close to the superior angle of the popliteal fossa.
In anatomy, extension is a movement of a joint that increases the angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extending the flexed (bent) elbow. Straightening of the arm would require extension at the elbow joint.
In the other extreme, the muscle's ability to flex the hip and extend the knee can be compromised in a position of full hip extension and knee flexion, due to passive insufficiency. The rectus femoris is a direct antagonist to the hamstrings , at the hip and at the knee.
The psoas is the primary hip flexor, assisted by the iliacus. The pectineus, the adductors longus, brevis, and magnus, as well as the tensor fasciae latae are also involved in flexion. The gluteus maximus is the main hip extensor, but the inferior portion of the adductor magnus also plays a role. The adductor group is responsible for hip adduction.