Abstract P497: Association Between Accelerometer-estimated Physical Activity Intensity and Heart Rate Variability: Mediation by Glycemic Measures and Triglycerides (from The Cardia Study)

Abstract

Introduction: We estimated cross-sectional associations between accelerometer-estimated light (LPA), moderate (MPA), and vigorous (VPA) intensity physical activity (PA) and heart rate variability (HRV), and tested mediation of these associations by glycemic control indices, blood lipids, and blood pressure. Hypothesis: PA is positively and independently associated with higher (improved) HRV. Glycemic measures are partial physiological mediators of these associations. Methods: Data were from 1,668 participants (X -age = 46 ± 4 yrs, 58% F, 40% black) in Year 20 (2005-06) of the Coronary Artery Risk Development in Young Adults (CARDIA) Fitness Study. The ActiGraph 7164 estimated participants’ mean min/d of LPA, MPA, and VPA over 7d. Three sequential 10-sec 12-lead ECG strips provided standard deviation of all normal RR intervals (SDNN) and root mean square of all successive RR intervals (rMSSD) HRV. Physiological mediators included fasting glucose and insulin as well as 2-hr oral glucose tolerance (OGTT), fasting triglycerides (TG), HDL-C, and systolic blood pressure (BP). Multiple linear regression, controlling for demographic and lifestyle confounders, assessed independent associations of PA with SDNN and rMSSD HRV per 1-SD. Mediation analyses computed the proportion of the PA-HRV associations attributable to physiological mediators. Results: Participants averaged 360.2 ± 83.8, 33.0 ± 22.0, and 2.7 ± 6.2 min/d of LPA, MPA, and VPA, respectively, with mean values for SDNN (32.6 ± 22.4 ms) and rMSSD (34.0 ± 24.8 ms) similar. VPA was associated with both HRV metrics (SDNN: std = .06 [.03, .10]; rMSSD: std = .08, [.05, .12]) and LPA with rMSSD only (std = .05, [.01, .08]). Fasting glucose and insulin mediated between 11.6%-20.7% of the association of VPA and LPA with HRV (Table). Triglycerides also mediated these associations (range: 9.6%-13.4%; Table). Conclusions: Accelerometer-estimated VPA and LPA were positively associated with higher HRV. These associations may be due most to glycemia and insulinemia.