Introduction: Breath-by-breath (BxB) data in modern metabolic carts exhibit high variability and are rarely filtered. With sampling intervals (SI) ≤30-s commonly incorporated, not accounting for outlier breaths can greatly inflate maximal oxygen consumption (V̇O2max) and reduce robustness. Purpose: this study attempted to address these issues by demonstrating that positive BxB outliers from unfiltered 30-s SI (V̇O2max30) wouldn’t differ in a meaningful (d≤0.15) way from 60-s SI (V̇O2max60), and 15-s SI (V̇O2max15) would increase in a significant enough fashion (d≥0.20) to be deemed a non-preferred SI. A novel, dual V̇O2plateau model was then created using ΔV̇O2max60-V̇O2max30 and ΔV̇O2max60-V̇O2non-max60 to form simple and objective sex-specific criterion guidelines for validation of V̇O2max60 assessment. Methods: Unfiltered BxB averages from the last 2-min of a graded exercise test to exhaustion were collected from female NCAA Division I cross-country runners (n=14). Results: V̇O2max60 and V̇O2max30 differed statistically but trivially from each other (2.91±0.28 vs 2.94±0.29 L/min; d=0.11). The differences between V̇O2max15 (3.01±0.33 L/min) and V̇O2max30 (d=0.23) and V̇O2max60 (d=0.33) were meaningful, confirming our hypotheses. Furthermore, four V̇O2max15 occurred before the final 2 min. V̇O2max60-V̇O2max30 (±0.05 L/min; <1%) and V̇O2max60-V̇O2non-max60 (±0.08 L/min; 1.60%) exhibited tight Bland-Altman 95% levels of agreement and coefficient of variation. V̇O2max60 validity can be confirmed using criteria of a dual V̇O2plateau model of Δ ≤0.08 L/min for ΔV̇O2max60-V̇O2max30 and Δ ≤0.15 L/min for ΔV̇O2max60-V̇O2non-max60. Conclusions: These simple guidelines can replace more subjective secondary confirmation markers to increase confidence in V̇O2max outcomes and determine need for verification testing without having to filter BxB data.

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 V̇ o ₂ 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 V̇ o ₂ and RER between 100% 5RP and submaximal paces were explored. Min-4 and min-5 Cohen's d effect sizes were <0.07 for V̇ o ₂ 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 V̇ o ₂ 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.