Which muscles are hamstrings and active during knee flexion?

Which muscles are hamstrings and active during knee flexion?

• A. Rectus Femoris; Vastus Medialis
• B. Biceps Femoris; Semimembranosus; Semitendinosus
• C. Semitendinosus; Popliteus
• D. Biceps Femoris; Semimembranosus; Semitendinosus

Answer: (D)

The main idea is identifying the true knee flexors on the back of the thigh. The three hamstring muscles are the biceps femoris (both heads), semimembranosus, and semitendinosus. They cross the knee from the posterior thigh to the tibia/fibula, so when they contract they pull the lower leg backward, producing knee flexion. The short head of the biceps femoris is included among the hamstrings, even though it doesn’t cross the hip, so it still helps bend the knee. The other muscles listed aren’t hamstrings. The rectus femoris and vastus medialis are part of the quadriceps, which extend the knee. The popliteus helps unlock the knee to start flexion but isn’t a hamstring. So the muscles that are hamstrings and active during knee flexion are the biceps femoris, semimembranosus, and semitendinosus.

The main idea is identifying the true knee flexors on the back of the thigh. The three hamstring muscles are the biceps femoris (both heads), semimembranosus, and semitendinosus. They cross the knee from the posterior thigh to the tibia/fibula, so when they contract they pull the lower leg backward, producing knee flexion. The short head of the biceps femoris is included among the hamstrings, even though it doesn’t cross the hip, so it still helps bend the knee.

The other muscles listed aren’t hamstrings. The rectus femoris and vastus medialis are part of the quadriceps, which extend the knee. The popliteus helps unlock the knee to start flexion but isn’t a hamstring. So the muscles that are hamstrings and active during knee flexion are the biceps femoris, semimembranosus, and semitendinosus.