Recreational and competitive athletes at levels from high school to National Collegiate Athletic Association Division I experience high rates of ankle injury, specifically to the lateral ligaments. (1-3) People who sustain an ankle sprain are at risk for developing chronic ankle instability (CAI), which is defined as subjective, repeated episodes of giving way after an initial ankle sprain. (4) Of these, 47% to 73% are estimated to experience recurrent sprains. (5,6) Two potential contributing factors to CAI are mechanical ankle instability (MAI), which is the physiologic laxity of the lateral ankle ligaments after a sprain, and functional ankle instability (FAI), which refers to episodes of instability linked to possible deficits in proprioception or neuromuscular control, not physiologic ligamentous laxity. (4) Despite potential differences in the nature of MAI and FAI, few authors to date have separated or differentiated between the two, (7) although these differences may play a role in the development of CAI. (8) A number of researchers have reported conflicting results regarding differences in proximal kinematics and landing kinetics between participants with and without CAI. Specifically, differences in knee kinematics were reported in 3 studies (9-11) but not in others. (12-14) Differences in hip kinematics were reported in one study of drop jumps (12) but not in other studies involving lateral hopping (15) or jump landing. (11) Differences in only peak lateral and peak anterior ground reaction force were reported in one study, (16) whereas greater vertical, medial, and posterior ground reaction forces were noted in another, (12) and differences in only posterior ground reaction force were seen in a third study. (15) Some of these conflicting results may be attributable to differences in the tasks, methods, and dependent variables used in these investigations. Additionally, if proximal joint differences during movement exist, they might influence the repetitive nature of CAI. Recent authors (17-19) have described impaired neuromuscular control in people with CAI, specifically in central motor programming and proximal joint motion patterns.