Abstract This study sought to develop an interval prone bridge fitness test to assess core stabilization in healthy adults (ages 18–39 years). Participants performed a prone bridge maneuver in alternating 15-sec work and 5-sec rest intervals with participants' RPE scores (0–10) recorded at the end of each work interval. The RPE score reported after 95 sec (RPE-95) was used to predict total interval prone bridge endurance time along with participants' self-reported level of physical activity (PA; sedentary = 0, low active = 1, active = 2, very active = 3). Multiple linear regression was employed to generate the following prediction equation (R = .86, SEE = 32.98 sec): Total time (sec) = 300.0 – (23.4 x RPE-95) + (17.7 x PA). Each predictor variable was statistically significant (RPE-95, p < .0001; PA, p = 0.006) and cross validation procedures using PRESS (predicted residual sum of squares) statistics revealed minimal shrinkage (Rp = .85 and SEEp = 32.89 sec). The mean and standard deviation (±SD) for the total duration of the interval prone bridge test and the RPE-95 data were 179.9 ± 65.2 sec and 6.3 ± 2.2, respectively. To assess test-retest reliability, a second test was completed about 48 hours after the first. The reliability study (n = 45) yielded an acceptable test-retest intraclass reliability coefficient (ICC = .95, SEM = 12.7 sec) when comparing total interval prone bridge endurance times across days. In summary, this interval prone bridge fitness test, and accompanying regression model, yields a relatively accurate estimate of total interval prone bridge test time in healthy men and women, using both RPE-95 and PA data.