Original Scientific Paper Vigorous physical activity and vagal modulation in young adults Luisa Soares-Miranda a , Gavin Sandercock c , Hugo Valente a,b , Susana Vale a , Rute Santos a and Jorge Mota a a Research Centre in Physical Activity, Health and Leisure, Faculty of Sport, University of Porto, b Faculty of Nutrition, University of Porto, Porto, Portugal and c Centre for Sports and Exercise Science, School of Biological Sciences, University of Essex, Colchester, UK Received 5 March 2009 Accepted 31 July 2009 Background Aerobic exercise leads to reduced sympathetic and increased cardiac vagal modulation, providing an antiarrhythmic effect. The optimal exercise intensity to promote this adaptation remains undefined. The aims of the present investigation were twofold. First, to examine differences in heart rate variability (HRV) measures in participants with different levels of objectively measured physical activity (PA). Second, to identify the characteristic of PA which most influences the cardiac autonomic nervous system (cANS) function in young adults. Methods Cross-sectional evaluation of 84 adults examining relationships between PA amount and intensities, measured by accelerometry, cANS function derived from HRV. Groups were created based on tertiles of PA and analysis of covariance was used to assess between-group differences in HRV. Stepwise regression analysis was used to determine the characteristic of PA, which best predicted vagal HRV indices. Results There were significantly higher levels of vagal HRV indices in the most active group compared with the least active group. Regression analysis revealed that the number of bouts of vigorous PA undertaken was the best predictor of the vagal HRV indices assessed. Conclusion This study suggests that vagal modulation is enhanced with high levels of PA and that it is the number of bouts of vigorous PA that is most closely associated with cANS function. Eur J Cardiovasc Prev Rehabil 00:000–000  c 2009 The European Society of Cardiology European Journal of Cardiovascular Prevention and Rehabilitation 2009, 00:000–000 Keywords: cardiac autonomic function, heart rate variability, physical activity Introduction Until 1995, the Center for Disease Control (CDC) and American College of Sports Medicine (ACSM) recommen- dations on physical activity (PA) and public health both recommended that adults should partake in moderate PA to maintain cardiovascular health and reduce the risk of coronary heart disease. When updated in 2007, the guidelines were changed to explicitly recommend the inclusion of vigorous PA [1]. Epidemiological evidence suggests that vigorous PA plays an important role in providing cardioprotective benefits [2,3]. Heart rate variability (HRV) is a noninvasive method to assess cardiac autonomic nervous system (cANS) function. Low HRV is indicative of a shift towards sympathetic predominance, and has prognostic value for all-cause mortality [4] and sudden cardiac death [5,6]. The mechanism by which HRV is related to mortality is probably because of an increased sym- pathetic activity reducing the threshold for ventricular fibrillation [7–9]. Aerobic exercise leads to a chronic reduction in sympathetic activity and increased vagal tone [2], providing an antiarrythmic effect [10]. The optimal exercise dose to promote autonomic benefits remains undefined. Correspondence to Luisa Soares-Miranda, Research Centre in Physical Activity, Health and Leisure, Faculty of Sport, University of Porto, Rua Dr Pla ´cido Costa, Porto 91-4200.450, Portugal Tel: +351 22 507 4785; fax: +351 22 550 0689; e-mail: luisasoaresmiranda@hotmail.com 1741-8267  c 2009 The European Society of Cardiology DOI: 10.1097/HJR.0b013e3283316cd1 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.