Review Question - QID 3345

Open chain exercises are movements where the end of the kinetic chain (the foot in this example) is moving freely and not fixed to the floor or a wall. Leg extensions and leg curls are examples shown in Figure A. These are also examples of isotonic contraction, defined by constant muscle contraction throughout the range of motion.

Both Miller's review and AAOS COR note that closed chain rehabilitation is emphasized in the early stages of ACL reconstruction rehabilitation because it allows physiologic co-contraction of the musculature around the knee. This is believed to decreases shear forces across the ACL reconstruction, whereas open-chain exercise can increase the shear stresses. The article by Miller and Croce, however tested 12 individuals using Cybex machines and found that there was actually greater hamstring muscle coactivation on EMG when performing isokinetic movements compared to closed-chain exercises.