Left Ventricular Vascular And Metabolic Adaptations To High-Intensity Interval And Moderate Intensity Continuous Training: A Randomized Trial In Healthy Middle-Aged Men

High-intensity interval training (HIIT) is a time-efficient way of obtaining the health benefits of exercise, although the cardiac effects of this training mode are incompletely known. We compared the effects of short-term HIIT and moderate intensity continuous training (MICT) interventions on myocardial perfusion and metabolism and cardiac function in healthy, sedentary, middle-aged men. Twenty-eight healthy, middle-aged men were randomized to either HIIT or MICT groups (n=14 in both) and underwent six cycle ergometer training sessions within 2 weeks (HIIT session: 4-6 x 30 s all-out cycling/4min recovery, MICT session 40-60 min at 60%. (V) over dot(O2peak)). Cardiac magnetic resonance imaging (CMRI) was performed to measure cardiac structure and function and positron emission tomography was used to measure myocardial perfusion at baseline and during adenosine stimulation, insulin-stimulated glucose uptake (MGU) and fasting free fatty acid uptake (MFFAU). End-diastolic and end-systolic volumes increased and ejection fraction slightly decreased with both training modes, although no other changes in CMRI were observed. MFFAU and basal myocardial perfusion remained unchanged. MGU was decreased by training (HIIT from 46.5 to 35.9; MICT from 47.4 to 44.4 mmol 100 g(-1) min(-1), P = 0.007 for time, P = 0.11 for group x time). Adenosine-stimulated myocardial perfusion responded differently to the training modes (change in mean HIIT: -19%; MICT: +9%; P = 0.03 for group x time interaction). HIIT and MICT induce similar metabolic and functional changes in the heart, although myocardial vascular hyperaemic reactivity is impaired after HIIT. This should be taken into account when prescribing very intense HIIT for previously untrained subjects.