Thermoplastic ankle foot orthoses (TAFO) control the foot during swing and initial contact of walking. Carbon fiber AFOs (CAFO) has the added ability to store and return energy at push off. The purpose of this report is to determine if plantarflexor power and function can be improved with a CAFO compared to a TAFO and identify factors that may be related to plantarflexor power improvement in two adults with reduced ankle muscle performance.Two participants with reduced ankle muscle performance completed a gait analysis and the 6 minute walk (6MW) test wearing each AFO. Physical function was higher in Participant 1 compared to Participant 2 as measured by the Foot and Ankle Ability Measure and walking speed.