Abnormal balance is a common clinical sign of mild traumatic brain injury (mTBI). Despite the clinical utility of reactive balance testing in other balance impaired populations, current clinical testing for mTBI does not include reactive postural responses (RPR) which may be more representative of a competitive athletic environment.PURPOSE: To examine differences in RPR in athletes with mTBI compared to healthy controls at three time points: within 48 hours after mTBI (Acute), within 24 hours of beginning return-to-play protocol (PreRTP), within 24 hours of being cleared for full return to competition (PostRTP).METHODS: RPR in 24 collegiate athletes with mTBI (F = 12, age 19.42 ± 1.28 years, BMI 25.18 ± 3.38 kg/m2) and 19 healthy controls (F = 8, age 19.67 ± 1.56 years, BMI 24.36 ± 2.98 kg/m2) were assessed using the Push and Release, with eyes closed, under single (ST) and dual-task (DT; concurrent verbal cognitive task) conditions at three time points after-mTBI (acute, PreRTP, PostRTP). Inertial sensors on the sternum, lumbar, and feet were used to assess time to stabilization (TTS). A sensor on the tester’s hand determined release time. Standardized effect sizes, mean differences, and confidence intervals were calculated for each time point for both tasks. RESULTS: There was a median of six days between PreRTP and PostRTP. The mTBI group had longer ST TTS (1.09 ± 0.315 s) than healthy controls (0.904 ± 0.157 s) at the acute time point by 0.187 s (Cohen’s d (d) = 0.73; 95% CI: [0.179, 0.204]), at PreRTP by 0.069 s (d = 0.32; 95% CI: [0.053, 0.084]) and shorter TTS at PostRTP by 0.034 s (d = -0.166; 95%CI: [-0.048,-0.019]). The mTBI group had longer DT TTS (1.23 ± 0.31 s) than healthy controls (0.984 ± 0.207 s) at the acute time point by 0.248 s (d = 0.92; 95% CI: [0.230, 0.267]), at PreRTP by 0.035 s (d = 0.18 ;95% CI: [0.021, 0.048]) and at PostRTP by 0.036 s (d = 0 .18 ; 95%CI: [0.022, 0.050]). CONCLUSIONS: There was a large difference in RPR between athletes with mTBI and healthy controls at the acute time point for both ST and DT; athletes with mTBI had slower time to stabilization. Differences in RPR were small at PreRTP and PostRTP for both ST and DT. These preliminary results suggest that mTBI affects reactive postural responses acutely following mTBI but these responses recover over time. Supported by PAC 12 Student Athlete Health & Wellbeing