Which muscles are active during knee extension?

• A. Gastrocnemius; Soleus
• B. Rectus Femoris; Vastus Medialis; Vastus Intermedius; Vastus Lateralis; Tensor Fasciae Latae (in 0-30 degrees flex)
• C. Biceps Femoris; Semimembranosus; Semitendinosus
• D. Popliteus; Plantaris

Answer: (B)

Knee extension is produced mainly by the quadriceps group. The rectus femoris, along with the vastus medialis, vastus intermedius, and vastus lateralis, generates the primary extensor moment across the knee, straightening the leg.

In addition, during very shallow flexion (0–30 degrees), the tensor fasciae latae can contribute to extension via its action on the iliotibial band, which helps stabilize and assist the knee as it moves toward full extension.

Other muscles listed don’t extend the knee. The hamstrings (biceps femoris, semimembranosus, semitendinosus) are knee flexors; the gastrocnemius crosses the knee but mainly acts as a plantarflexor of the ankle and can oppose extension depending on position. Popliteus helps unlock the knee, and the plantaris has only a minor, variable role.