Two weeks of high-intensity interval training improves novel but not traditional cardiovascular disease risk factors in adolescents

Abstract

BACKGROUND: High-intensity interval training (HIIT) improves traditional cardiovascular disease (CVD) risk factors in adolescents, but no study has identified the influence of HIIT on endothelial and autonomic function in this group. METHODS: Thirteen 13-14 y old adolescents (6 girls) completed six HIIT sessions over two weeks. Each training session consisted of 8-10 x 1-min repetitions cycling at 90% peak power, interspersed with 75 s of unloaded cycling. Traditional (triglycerides, cholesterol, glucose, insulin and blood pressure) and novel (flow mediated dilation; FMD, heart rate variability; HRV) CVD risk factors were assessed in a fasted and postprandial state before (PRE), 1-day (POST-1D) and 3-days after (POST-3D) training. Aerobic fitness was determined PRE and POST-3D. RESULTS: Two weeks of HIIT had no effect on aerobic fitness or traditional CVD risk factors determined in the fasted or postprandial state (P>0.15). Compared to PRE, fasted FMD was improved POST-1D (P=0.003, effect size (ES)=0.70) but not POST-3D (P=0.32, ES=0.22). Fasted FMD was greater POST-1D compared to POST-3D (P=0.04, ES=0.48). Compared to PRE, postprandial FMD was greater POST-1D (P<0.001, ES=1.01) and POST-3D (P=0.01, ES=0.60. Fasted HRV was greater POST-1D (P=0.001, ES=0.71) and POST-3D (P=0.02, ES=0.44). The test meal lowered HRV in all trials (P<0.001, ES=0.59), but there were no differences in postprandial HRV between trials (P>0.32 for all). CONCLUSIONS: Two weeks of HIIT enhanced endothelial function and HRV without improvements in traditional CVD risk factors. However, most of this favourable adaptation was lost POST-3D, suggesting that regularly performing high-intensity exercise is needed to maintain these benefits.