Backward walking offers a unique challenge to balance and ambulation. This study investigated the characteristics of spatiotemporal gait factors and ankle kinematics during backward walking in people with chronic ankle instability. Sixteen subjects with chronic ankle instability and 16 able-bodied controls walked on a treadmill at their self-selected speed under backward and forward walking conditions. Gait speed, cadence, double limb support percentage, stride time variability, and threedimensional ankle kinematics were compared between groups and conditions. During backward walking, both groups had significantly slower gait speed, lower cadence, and greater stride time variability. In addition, under backward walking condition, subjects in both groups demonstrated significant sagittal and frontal kinematic alternations, such as greater dorsiflexion and inversion following initial contact (0-27.7%, 0-25.0% of gait cycle respectively, p < 0.001). However, there were no significant differences between groups in any of the measured outcomes. This indicates that subjects with chronic ankle instability adapt to self-selected speed backward walking similarly to healthy controls. Assessments with more challenging tasks, such as backward walking with dual task and backward walking at fast speed, may be more appropriate for testing gait impairments related to chronic ankle instability. Chronic ankle instability (CAI) may be present in up to 40% of individuals who have previously experienced lateral ankle sprain 1. CAI is characterized by repetitive episodes and subjective feeling of ankle 'giving way' , and symptoms such as pain, swelling and limited motion 2-4. Compared to healthy controls, individuals with CAI report quality-of-life deficits and functional limitations in addition to the physical impairments 2,5,6. While mechanical factors, such as ankle ligaments hyperlaxity, may be responsible for CAI in some patients 2 , it can occur even when the mechanical constraints at the ankle are intact 7. Recent evidence suggest that CAI can be explained by sensorimotor deficits 3,7,8. Arthrogenic neuromuscular inhibition 9,10 , ankle muscle weakness 4,11 , reduced ankle range of motion 3,9 , impaired sense of joint position 12 , and postural control are found in CAI. Altered movement patterns during functional tasks, including walking, are often described in individuals with CAI 13. During walking, subjects with CAI may exhibit typical kinematic patterns of increased ankle inversion and a laterally deviated center of pressure throughout the stance phase of gait 6. Conversely, Chinn et al. 5 reported that CAI subjects demonstrated more inversion while jogging but not while walking. Linear variability measures that investigated the amplitude of variability, such as coefficient of variation, and non-linear variability approaches that evaluated the dynamic aspects of variability using mathematical tools related to chaos theory, have both reported differences in gait variability between individuals with and without CAI. For examp...