Clark, AW, Goedeke, MK, Cunningham, SR, Rockwell, DE, Lehecka, BJ, Manske, RC, and Smith, BS. Effects of pelvic and core strength training on high school cross-country race times. J Strength Cond Res 31(8): 2289–2295, 2017—There is only limited research examining the effect of pelvic and core strength training on running performance. Pelvic and core muscle fatigue is believed to contribute to excess motion along frontal and transverse planes which decreases efficiency in normal sagittal plane running motions. The purpose of this study was to determine whether adding a 6-week pelvic and core strengthening program resulted in decreased race times in high school cross-country runners. Thirty-five high school cross-country runners (14–19 years old) from 2 high schools were randomly assigned to a strengthening group (experimental) or a nonstrengthening group (control). All participants completed 4 standardized isometric strength tests for hip abductors, adductors, extensors, and core musculature in a test-retest design. The experimental group performed a 6-week pelvic and core strengthening program along with their normal training. Participants in the control group performed their normal training without additional pelvic and core strengthening. Baseline, 3-week, and 6-week race times were collected using a repeated measures design. No significant interaction between experimental and control groups regarding decreasing race times and increasing pelvic and core musculature strength occurred over the 6-week study period. Both groups increased strength and decreased overall race times. Clinically significant findings reveal a 6-week pelvic and core stability strengthening program 3 times a week in addition to coach led team training may help decrease race times.