The Effect of Fixed Ankle and Knee Joints on Postural Stability and Muscle Activity

Abstract

[Purpose] This study examined postural stability and muscle activity when limitations were placed on the ankle and knee joints. [Subjects] Forty-eight healthy young adults were randomly assigned to one of three groups: a fixed-ankle group (6 males, 9 females), a fixed-ankle-and-knee group (9 males, 7 females), and a non-fixed group (7 males, 10 females). [Methods] The fixed-ankle subjects were limited using orthopedic fiberglass casting tape and elastic bandages and the fixed-ankle-and-knee subjects were additionally limited using a knee immobilizer. There were no limitations on the ankle and knee joints of the non-fixed group subjects. We measured postural stability and muscle activities of the ankle and knee muscles. [Results] There were differences in the muscle activities of the tibialis anterior, median gastrocnemius, and rectus femoris between the groups. The greatest muscle activity in the tibialis anterior was shown by the non-fixed group, and the fixed-ankle group showed the greatest rectus femoris and gastrocnemius activities. There were significant differences in the overall stability index, anterior-posterior stability index, and medial-lateral stability index. All three indices were the lowest for the non-fixed group. [Conclusion] A fixed ankle or knee reduces muscle activity which in turn lowers postural stability.