Regular physical training upregulates enzymatic and non-enzymatic antioxidant systems, which may lower chronic oxidative stress. Few human data are available, however, at the community level on the relationship between physical fitness and oxidative stress. PURPOSE: To measure the relationship between self-reported physical fitness level and plasma biomarkers for oxidative stress and antioxidant capacity while controlling for important confounders including age, gender, and body mass index (BMI). METHODS: A large community group of males (40%) and females (60%) (N=1,002), varying widely in age (18 to 85 years) and BMI (16.7 to 52.7 kg/m2) served as subjects. Each completed an extensive medical/health questionnaire, were measured for body weight and height, and provided two overnight fasted blood samples separated by 12 weeks. Physical fitness levels were self-reported using a ten-point Likert scale, with one corresponding to low fitness and ten to high fitness. All plasma biomarkers were assayed and averaged from the two blood samples. Ferric reducing ability of plasma (FRAP) and oxygen radical absorbance capacity (ORAC) served as plasma antioxidant capacity markers. Oxidative stress was determined by plasma levels of F2-isoprostanes, and was assayed using gas chromatography mass spectrometry. Tertile categories were created based on self-reported fitness levels, with differences in outcome measures analyzed using the general linear models procedure in SAS while controlling for age, gender, smoking, and BMI. For variables with a significant test for trend, least-squares means were compared across tertile categories, with Bonferroni's adjustment for multiple comparisons. RESULTS: Significant tests for trend were found for plasma F2-isoprostanes (P=0.008) but not plasma FRAP or ORAC. Plasma F2-isoprostanes were significantly lower for the high (-8%) self-reported physical fitness levels when compared to low. CONCLUSIONS: These data indicate that oxidative stress but not antioxidant capacity is related to self-reported physical fitness level at the community level. Plasma F2-isoprostanes were reduced across low to high tertiles of self-reported physical fitness level. Supported by grants from Coca-Cola and Quercegen Pharma.