Cardiac remodeling after six weeks of high-intensity interval training to exhaustion in endurance-trained males

High-intensity interval training (HIIT) improves physical performance of endurance athletes, although studies examining its cardiovascular effects are sparse. We evaluated the impact of HIIT on blood pressure, heart rate, and cardiac cavities' size and function in endurance-trained adults. Seventeen endurance-trained men underwent 24-h ambulatory blood pressure monitoring and Doppler echocardiography at baseline and after 6 wk of HIIT. Participants were divided into 2 groups [85% maximal aerobic power (HIIT85). n = 8 and 115% maximal aerobic power (HIIT115),n = 9] to compare the impact of different HIIT intensities. Ambulatory blood pressure monitoring and cardiac chambers' size and function were similar between groups at baseline. HIIT reduced heart rate (55 +/- 8 vs. 51 +/- 7 beats/min; P = 0.003), systolic blood pressure (121 +/- 11 vs. 118 +/- 9 mmHg; P = 0.01), mean arterial pressure (90 +/- 8 vs. 89 +/- 6 mmHg; P = 0.03), and pulse pressure (52 +/- 6 vs. 49 +/- 5 mmHg; P = 0.01) irrespective of training intensity. Left atrium volumes increased after HIIT (maximal: 50 +/- 14 vs. 54 +/- 14 mL; P= 0.02; minimal: 15 +/- 5 vs. 20 +/- 8 mL; P = 0.01) in both groups. Right ventricle global longitudinal strain lowered after training in the HIIT85 group only (20 +/- 4 vs. 17 +/- 3%, P = 0.04). In endurance-trained men, 6 wk of HIIT reduced systolic blood pressure and mean arterial pressure and increased left atrium volumes irrespective of training intensity, whereas submaximal HIIT deteriorated right ventricle systolic function. NEW & NOTEWORTHY The novel findings of this study are that 6 wk of high-intensity interval training increases left atrial volumes irrespective of training intensity (85 or 115% maximal aerobic power), whereas the submaximal training decreases right ventricular systolic function in endurance-trained men. These results may help identify the exercise threshold for potential toxicity of intense exercise training for at-risk individuals and ideal exercise training regimens conferring optimal cardiovascular protection and adapted endurance training for athletes.