How does the popliteus muscle rotate the knee joint? This depends on which attachment is free to move. If the body is in open-chain position in which the foot is free to move, then the popliteus medially rotates the tibia (leg) at the knee joint. This is usually considered to me the standard action because the distal attachment moves and the proximal attachment stays fixed. However, if the body is in closed-chain position in which the foot is against a stable surface (such as the ground), then the popliteus will laterally rotate the femur (thigh) at the knee joint. This is considered to be a reverse action because the proximal attachment moves and the distal attachment is fixed. In the lower extremity, it is functionally more likely that closed-chain reverse actions occur because the foot is so often against the ground, so perhaps reverse actions are really the standard actions. What is more important to realize with muscle contraction is that the pull is simply toward the center, pulling equally on both attachments. Whichever one is less resistant to moving is the one that will move. A muscle does not and cannot choose which attachment moves. When directed to contract by the nervous system, it simply pulls toward its center. - Joe Muscolino
Posted on: Tue, 10 Jun 2014 12:52:29 +0000
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