The semitendinosus does what action?

The semitendinosus does what action?

• A. Extends thigh at hip
• B. Flexes leg
• C. Medially rotates tibia
• D. Extends knee

Answer: (B)

The semitendinosus is a hamstring muscle that crosses both the hip and knee joints, so it has actions at two joints. Its role at the knee is to bend (flex) the leg, which is the primary movement most people think of when considering this muscle. While it also helps extend the thigh at the hip and, when the knee is flexed, can assist with medially rotating the tibia, the single best description of its main action here is flexing the leg. Extending the knee is actually accomplished mainly by the quadriceps, not the hamstrings.

The semitendinosus is a hamstring muscle that crosses both the hip and knee joints, so it has actions at two joints. Its role at the knee is to bend (flex) the leg, which is the primary movement most people think of when considering this muscle. While it also helps extend the thigh at the hip and, when the knee is flexed, can assist with medially rotating the tibia, the single best description of its main action here is flexing the leg. Extending the knee is actually accomplished mainly by the quadriceps, not the hamstrings.