High-Intensity Interval Training Improves Left Ventricular Contractile Function YU-CHIEH AQ1 HUANG 1 , HSING-HUA TSAI 1 , TIEH-CHENG FU 2,3 , CHIH-CHIN HSU 2,3 , and JONG-SHYAN WANG 1,2,3 1 Healthy Aging Research Center, Graduate Institute of Rehabilitation Science, Medical Collage, Chang Gung University, Tao-Yuan, TAIWAN; 2 Department of Physical Medicine and Rehabilitation, Chang Gung Memorial Hospital, Keelung, TAIWAN; and 3 Heart Failure Center, Chang Gung Memorial Hospital, Keelung, TAIWAN ABSTRACT HUANG, Y.-C., H.-H. TSAI, T.-C. FU, C.-C. HSU, and J.-S. WANG. High-Intensity Interval Training Improves Left Ventricular Contractile Function. Med. Sci. Sports Exerc., Vol. 51, No. 7, pp. 00–00, 2019. Introduction: Improved myocardial contractility is a critical circulatory adaptation to exercise training. However, the types of exercise that enhance left ventricular (LV) contractile and diastolic functions have not yet been established. This study investigated how high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) influence LV mechanics during exercise. Methods: Fifty-four healthy sedentary men were randomized to engage in either HIIT (3-min inter- vals at 40% and 80% of V ˙ O 2max , n = 18) or MICT (sustained 60% of V ˙ O 2max , n = 18) for 30 min·d -1 , 5 d·wk -1 for 6 wk or to a control group (n = 18) that did not engage in exercise intervention. LV mechanics during semiupright bicycle exercise tests were measured by two- dimensional speckle-tracking echocardiography. Results: Before the interventions, acute bicycle exercise increased (i) peak basal/apical radial and circumferential and peak longitudinal strains and strain rates, (ii) peak basal/apical rotations and torsion, and (iii) peak systolic twisting and early diastolic untwisting velocities in the LV. After the interventions, the HIIT group exhibited greater LV mass and diastolic internal diam- eter as well as higher ratio of E wave to A wave and early diastolic propagation velocity than did the MICT group. Despite decreased peak apical rotation and torsion, HIIT enhanced peak apical radial strain and strain rate as well as shortened the time to reach peak untwisting ve- locity in the LV during exercise. However, the LV mechanics during exercise were unchanged in the control group. Conclusion: HIIT but not MICT induces eccentric myocardial hypertrophy. Moreover, HIIT effectively improves the LV mechanics during exercise by increasing con- tractile and diastolic functions. Key Words: EXERCISE, HEART, CONTRACTILITY, ECHOCARDIOGRAPHY T he helical myocardial fiber architecture plays a critical role in left ventricular (LV) mechanics (1). The left ventricle undergoes architectural alterations in many heart diseases, leading to inefficient cardiac function (2). Reg- ular physical exercise may lead to changes in myocardial structure and function (3). Endurance training may cause ec- centric LV hypertrophy (4), whereas strength training may re- sult in concentric LV hypertrophy (5). However, few studies have elucidated the distinct effects of different training regi- mens on LV mechanics. High levels of physical activity and aerobic capacity are strongly associated with low risk of cardiovascular disease and mortality (6,7). Recent studies further demonstrated that high-intensity interval training (HIIT) significantly improved O 2 uptake efficiency by enhancing hemodynamic responses to exercise than traditional moderate-intensity continuous training (MICT) in heart failure patients (8,9) and healthy sed- entary men (10). However, an effective training strategy that promotes cardiac inotropic and lusitropic effects by improving LV mechanics has not yet been established. Stress echocardiography has been reported to be a more reasonable and assessable approach to clarifying the global effects of cardiac training (11,12). Analyzing strain and strain rate (SR) through speckle-tracking echocardiography is a new noninvasive method for more sensitively detecting myocardial dysfunction than traditional echocardiographic indices (e.g., ejection fraction) (13). Previously studies had been noticed the different strain performances in the left ventricle among healthy individuals, athletes, and cardiac patients (14–16). The aim of the present study was to establish an effective training strategy for improving LV contractile and diastolic functions during exercise. To answer the previously mentioned questions, this study comprehensively clarified how HIIT (3-min intervals at 40% and 80% of maximal O 2 consumption (V ˙ O 2max )) or MICT (sustained 60% of V ˙ O 2max ) for 6-wk affected LV architecture and mechanics (i.e., strain, SR, rotation, torsion, and twist) at rest or during exercise in sedentary men using two-dimensional (2D) speckle-tracking echocardiography. Address for correspondence: Jong-Shyan Wang, Ph.D., Graduate Institute of Rehabilitation Science, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Tao-Yuan 333, Taiwan; E-mail: s5492@mail.cgu.edu.tw. Submitted for publication January 2018. Accepted for publication February 2019. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.acsm-msse.org). 0195-9131/19/5107-0000/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE ® Copyright © 2019 by the American College of Sports Medicine DOI: 10.1249/MSS.0000000000001931 1 Copyright © 2019 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. Copyedited by: Cabrera, Karlyn D.