Introduction: Ankle sprains from excessive inversion are the most frequent sports- related injury. Common ankle prophylactics are designed to prevent injury by limiting excessive ankle inversion, yet may restrict other ankle motions leading to repeated re-injury. Females are twice as likely as males to suffer an ankle sprain, however, it is unknown if a sex dimorphism in ankle biomechanics exists when wearing ankle prophylactics, and whether differences in the peroneal musculature exist between sexes. Purpose: To quantify the ability of ankle prophylactics (Ankle Roll Guard (ARG), Brace, Control, and Tape) to prevent excessive ankle inversion during a sudden inversion event, and determine whether the effectiveness of the ankle prophylactics and in vivo peroneal muscle parameters differ between sexes. Methods: Thirty-two (16 male and 16 female) participants had dominant limb (i.e., braced) frontal and sagittal plane ankle biomechanics, including peak inversion and plantarflexion angle and range of motion (ROM), and time to peak inversion, quantified during the sudden inversion event with four prophylactic conditions (ARG, Brace, Control, and Tape) and peroneal muscle parameters recorded. With each prophylactic, participants performed five successful trials of the sudden inversion event. Peroneal muscle parameters, including physiological cross-sectional area (PCSA) and stiffness, were quantified in vivo using ultrasound shear-wave elastography, while peroneal strength was measured with an isokinetic dynamometer. Statistical Analysis: All kinematic variables were submitted to a RM ANOVA to test for main effect and interaction of brace (ARG, Brace, Control, and Tape) and sex (male and female). Peroneal muscle parameters were also submitted to independent samples t-test to test the effect of sex. Results: A prophylactic by sex interaction (p = 0.010), revealed females exhibit greater ankle inversion ROM with Control and ARG (p = 0.001, p = 0.010) compared to males. Females also exhibited greater ankle inversion ROM with ARG compared to Brace (p = 0.001), and Control compared to Brace and Tape (p \u3c 0.001, p \u3c 0.001), while males exhibited no significant difference between any prophylactic condition (p \u3e 0.05). Ankle prophylactic impacted ankle inversion ROM (p \u3c 0.001), time to peak inversion (p \u3c 0.001), and peak plantarflexion angle (p \u3c 0.001) and ROM (p \u3c 0.001). Females exhibited smaller peroneal PCSA (p = 0.002) and dorsiflexion strength (p = 0.047), but sex had no significant effect on peroneal strength (p =0.142) or stiffness (p \u3e 0.05). Conclusion: The protective benefits of ankle prophylactics may depend on the specific device and sex of the user. With the lace-up brace and tape, participants decreased ankle biomechanics associated with injury, but this protective benefit was only evident for females. Females exhibited a sex dimorphism in ankle biomechanics during the sudden inversion event, and smaller and weaker peroneals that may contribute to the sex disparity in injury rate
