Chen LY, et al. - In CARDIA, an observational cohort study, researchers analyzed the value of cardiorespiratory fitness vs adiposity in determining heart rate variability (HRV). The study sample consisted of 2,316 participants with HRV measured in 2005-2006 (Year 20), and graded exercise test duration (GXTd) and adiposity measures (BMI, waist circumference) from 1985-1986 (baseline) and 2005-2006. A longitudinal decrease in GXTd was significantly related to 55% and 94% higher odds of unfavorable standard deviation of all normal RR intervals and square root of the mean of the squares of differences between all successive RR intervals, respectively, at Year 20 vs no change/increase in GXTd. Compared to adiposity, cardiorespiratory fitness might be a stronger determinant of HRV.