The purpose of this study was to compare the support effectiveness of three ankle orthoses before, during, and after a 90 minute softball practice. The effect of each support method on the athletes' base running ability was also assessed. Twenty-four ankles with no history of ankle pathology were divided into three groups (n = 8), and randomly assigned to wear one of the ankle devices. Passive inversion-eversion ROM was measured on an ankle stability test instrument during five testing sessions: 1) pre-support, 2) pre-exercise, 3) 20 minutes during exercise, 4) 40 minutes during exercise, and 5) post-exercise. The data analyses revealed significant differences in support effectiveness among the three orthoses (p < 0.01). The support provided post-exercise by the Swede-O was reduced by 35% compared to its initial level of support. The support reductions for the Air-Stirrup and the Ankle Ligament Protector (ALP) were 12% and 8%, respectively. The application of the ALP and the Swede-O orthoses had no significant effect on the athletes' ability to run the bases; while the Air-Stirrup application resulted in significantly slower base running times. These results suggest that the ALP may be more effective than the other orthoses tested in guarding against initial inversion sprain trauma and protecting the ankle joint against chronic re-injury. J Orthop Sports Phys Ther 1990;11(10):453-466.