Review Question - QID 678

A "closed chain exercise" is one in which the distal end of the extremity is fixed, allowing axial loading of the extremity with co-contracture of muscles decreasing stress across that joint.

Closed chain exercises are preferred for any rehabilitation protocol that wants to minimize stress across a potentially unstable joint. After ACL reconstruction it is important to begin motion and strengthening but not stress the reconstructed ligament which may lead to loss of stability or failure.

An example of a closed chain exercise of the quadriceps is a squat or leg press in which the foot is fixed against the floor/plate and both the quadriceps and hamstrings can contract together keeping the knee joint stable and preventing excess stress across the reconstructed ACL. An example of an open chain exercise of the quadriceps is a seated leg extension in which the foot is not fixed and the quadriceps contract in isolation. This creates a strong anterior pull on the tibia which can lead to excess stress on the ACL graft.

Beynnon et al. present a review on the behavior of ACL grafts during rehabilitation. They found that exercises that produce the least amount of stress across an ACL graft are either dominated by hamstring muscle contraction, involve quadriceps muscle activity with the knee flexed at 60° or greater, or involve active knee motion between 35° and 90° of flexion.

Illustration A is an example of a squat, which is a closed chain exercise. Notice the feet are fixed in place against the floor. Illustration B is an example of a seated leg extension, which is an open chain exercise. Notice the feet are not fixed in place and no axial loading or co-contracture can occur.

Incorrect Answers:
Answer A: Eccentric contractions are when a muscle is lengthening during the contraction.
Answer C: Open chain exercises involve the distal end of the extremity being freely mobile in space and a muscle group acts in isolation.
Answer D: Proprioceptive neuromuscular facilitation (PNF) is the use of muscle stretch to augment contraction.
Answer E: An isometric contraction is when the muscle length remains constant as it contract.