Background: Blood pressure and peak oxygen uptake (VO 2peak ) are strong independent predictors of all-cause and cardiovascular mortality. A VO 2peak of 8 METs or greater is associated with greater cardiovascular health and probability of survival, whereas individuals with a VO 2peak less than 8 METs are at greater risk for cardiovascular and all-cause mortality. Increasing physical activity in insufficiently active adults is associated with improvements in blood pressure (BP). Additionally, the relationship between an individual’s baseline VO 2peak and BP responses following a walking intervention are unknown. Therefore, we examined the change in BP in individuals stratified based on baseline VO 2peak (< 8 METs & ≥ 8 METs). We hypothesized that those with a VO 2peak < 8 METs would see greater blood pressure responses compared to those with a VO 2peak ≥ 8 METs. Methods: Cross-sectional, secondary analyses were carried out on data from a previously conducted clinical trial that included insufficiently active (as determined by accelerometry) individuals (N=518). Subjects underwent BP measurements, anthropometric testing, and a treadmill-based VO 2peak test with ventilatory gas exchange assessment to determine VO 2peak . Subjects with missing data were excluded from analyses. Additionally, only valid VO 2peak tests (≥90% age-predicted HR max , RER > 1.0) were included. Three hundred and sixty nine individuals had BP measured and met the criteria for a valid VO 2peak test. Subjects were then stratified based on baseline VO 2peak : low fit (<8 METS), and high fit (≥8 METS). Linear mixed model analyses were carried out to examine main effects (time and VO 2peak category) of the walking intervention on BP. The interaction of time and VO 2peak category was examined as well. Data are presented as means ± SD with α set at 0.05. Results: Eighty-one individuals had a VO 2peak greater than or equal to 8 METs (age = 41.9±10.0 years; BMI = 28.8±4.8; VO 2peak = 31.1±3.1 mL/kg/min; Males/Females = 55/26). Two-hundred and eighty-eight individuals had a VO2peak less than 8 METs (age = 45.9±8.6 years; BMI = 34.4±6.5; VO 2peak = 22.4±3.2 mL/kg/min; Males/Females = 75/213). There was a significant group by time interaction effect for changes in systolic BP (≥ 8 METs: Pre = 120.8±1.4, Post = 123.0±1.6 mmHg, < 8 METs: Pre = 122.1±0.7, Post = 120.4±1.0 mmHg) (p = 0.03). There was no significant effects found for DBP. Conclusions: These secondary analyses found that SBP significantly decreased following a 6-month walking intervention in individuals with low-fitness. These data suggest that those with lower baseline CRF are likely to have greater declines in SBP. Supported by NIH R01CA1989 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.