AbstractBackgroundCardiopulmonary exercise testing (CPET), the gold‐standard method to quantify cardiorespiratory fitness (CRF), is not always feasible due to cost, access, and burden. The usual‐paced 400 m long distance corridor walk (LDCW), a measure of mobility among older adults, may provide an alternate method to assess CRF. The purpose of this study was to develop and validate an estimating equation to estimate VO₂peak from average 400 m walking speed (WS) among participants in the Study of Muscle, Mobility and Aging (SOMMA).MethodsAt baseline, women (58%) and men age 70 years and older enrolled in SOMMA (N = 820, 76.2 ± 4.9 years, 86% Non‐Hispanic White) completed a 400 m LDCW (400 m WS = 400 m/completion time in seconds) and symptom‐limited maximal CPET (Modified Balke Protocol). VO₂peak (mL/kg/min) was considered the highest 30‐second average oxygen consumption during CPET. Other covariates included: age, sex, race, physical activity (7‐day wrist‐worn accelerometer), physical function (Short Physical Performance Battery, range 0–12), perceived physical fatigability (Pittsburgh Fatigability Scale, range 0–50), and Borg Rating of Perceived Exertion (RPE, range 6–20) at completion of the 400 m LDCW. Stepwise linear regression was used. Internal validation was completed using data‐splitting method (70%; 30%).ResultsMean VO₂peak was 20.2 ± 4.8 mL/kg/min and mean 400 m WS was 1.06 ± 0.2 m/s. Each 0.05 m/s increment in 400 m WS was associated with a 0.40 mL/kg/min higher VO₂peak after covariate adjustment. An estimating equation including 400 m WS, age, sex, race, and RPE was developed. Internal validation showed low overall bias (−0.26) and strong correlation (r = 0.71) between predicted and measured VO₂peak values. Bland–Altman plot and regression analyses indicated predicted VO₂peak was an acceptable alternative, despite mean underestimation of 4.53 mL/kg/min among the highly fit.ConclusionsUsual‐paced 400 m LDCW strongly correlates with direct measures of CRF during CPET in older adults with lower fitness and can be used to test both fitness and function.