During midstance, the knee may rely on passive bone/ligament lock because which muscle group goes quiet?

During midstance, the knee may rely on passive bone/ligament lock because which muscle group goes quiet?

• A. Hip flexors
• B. Plantarflexors
• C. Hamstrings only
• D. Quadriceps

Answer: (D)

During midstance the knee can become stabilized without active muscle work through a passive locking of the joint, often described by the knee’s screw-home mechanism. When the leg is bearing weight and the knee nears full extension, the bones and ligaments guide the joint into a mechanically locked position, which minimizes the need for muscle effort to hold it. If the quadriceps relax, there isn’t an active pull on the tibia that would oppose this extended, locked position. The passive structures—the joint surfaces and supporting ligaments—take over, keeping the knee extended and stable with little muscular activation. If the quadriceps remained active, they would tend to adjust or disrupt that passive lock by generating anterior tibial pull and altering the alignment needed for the knee to stay locked. Other muscle groups aren’t what enables this passive stabilization during midstance; their activity would either not contribute to or would oppose the locked extended state.

During midstance the knee can become stabilized without active muscle work through a passive locking of the joint, often described by the knee’s screw-home mechanism. When the leg is bearing weight and the knee nears full extension, the bones and ligaments guide the joint into a mechanically locked position, which minimizes the need for muscle effort to hold it.

If the quadriceps relax, there isn’t an active pull on the tibia that would oppose this extended, locked position. The passive structures—the joint surfaces and supporting ligaments—take over, keeping the knee extended and stable with little muscular activation. If the quadriceps remained active, they would tend to adjust or disrupt that passive lock by generating anterior tibial pull and altering the alignment needed for the knee to stay locked.

Other muscle groups aren’t what enables this passive stabilization during midstance; their activity would either not contribute to or would oppose the locked extended state.