15 active young adults with self-reported chronic ankle instability were included in the study which aimed to investigate lower extremity muscle function under various footwear conditions. In the crossover design, participants were randomized to the order of the different footwear conditions to be used during the functional tests; ankle destabilization boot, ankle destabilization sandal, or standard athletic shoes. Surface electromyography was used to investigate muscle activity and time to muscle activation in muscles of the lower extremity, including anterior tibialis, fibularis longus, lateral gastrocnemius, rectus femoris, biceps femoris, and gluteus medius, during functional tests. The results of this study indicated that ankle destabilization devices demonstrated significant changes in the activation patterns of the fibularis longus during functional tests, with the exception of the timing of activation prior to initial contact of the foot while walking.