Running Economy Assessment at 90% of 5-km Pace Is More Informative Than Lower Intensities Among Women's NCAA Division I Cross-Country Competitors.

O'Neal, EK, Knight, SN, Bowling, LR, Scudamore, EM, Scudamore, V, and Waldman, HS. Running economy assessment at 90% of 5-km pace is more informative than lower intensities among women's NCAA Division I cross-country competitors. J Strength Cond Res XX(X): 000-000, 2026-National Collegiate Athletics Association (NCAA) women's cross-country (XC) runners compete at distances of 5-6 km producing respiratory exchange ratios (RER) > 0.99 at race pace. This prevents calculation of the most sensitive unit of running economy (RE) metabolic cost (MC). This study first established the steady-state characteristics of V̇o2 and RER using 60-s sampling intervals during the last 2-minute of 5-minute RE bouts at individual 5-km race pace (5RP) and 70, 80, and 90% 5RP of 13 NCAA Division I Women's XC runners. After confirming steady state was not compromised by intensity, the relationship of V̇o2 and RER between 100% 5RP and submaximal paces were explored. Min-4 and min-5 Cohen's d effect sizes were <0.07 for V̇o2 at all submaximal velocities, and RER at lowest (70%; d = 0.25) and highest (90%; d = 0.29) intensities were similar. Strong relationships (r ≥ 0.89; p < 0.001) between V̇o2 for 70, 80, and 90% to 5RP were exhibited. However, RER for 70% (r = -0.10) and 80% (r = -0.12) both produced inverse, nonsignificant relationships to 5RP. By contrast, 90% produced an r = 0.62 (p = 0.03), and no runner's RER exceeded 0.99. For performance analysts and NCAA Women's XC coaches using RE to detect training intervention efficacy, metabolic steady state is (a) uncompromised at 90% of 5RP, (b) permits MC calculation, and (c) better reflects 5RP metabolic profile than lower intensities.