Myocardial Adaptation to High-Intensity (Interval) Training in Previously Untrained Men With a Longitudinal Cardiovascular Magnetic Resonance Imaging Study (Running Study and Heart Trial)

Background-To prospectively evaluate whether short-term high-intensity (interval) training (HI(I) T) induces detectable morphological cardiac changes in previously untrained men in cardiovascular magnetic resonance imaging. Methods and Results-Eighty-four untrained volunteers were randomly assigned to a HI(I) T group (n=42; 44.1 +/- 4.7 years) or an inactive control group (n=42; 42.3 +/- 5.6 years). HI(I) T focused on interval runs (intensity: 95%-105% of individually calculated heart rate at the anaerobic threshold). Before and after 16 weeks, all subjects underwent physiological examination, stepwise treadmill test with blood lactate analysis, and contrast-enhanced cardiovascular magnetic resonance imaging (cine, tagging, and delayed enhancement). Indexed left ventricular (LV) and right ventricular (RV) volume (LV, 77.1 +/- 8.5-83.9 +/- 8.6; RV, 80.5 +/- 8.5-86.6 +/- 8.1) and mass (LV, 58.2 +/- 6.4-63.4 +/- 8.1; RV, 14.8 +/- 1.7-16.1 +/- 2.1) significantly increased with HI(I) T. Changes in LV and RV morphological parameters with HI(I) T were highly correlated with an increase in maximal aerobic capacity (VO2max) and a decrease in blood lactate concentration at the anaerobic threshold. Mean LV and RV remodeling index of HI(I) T group did not alter with training (0.76 +/- 0.09 and 0.24 +/- 0.10 g/mL, respectively [P=0.97 and P=0.72]), indicating balanced cardiac adaptation. Myocardial circumferential strain decreased after HI(I) T within all 6 basal segments (anteroseptal, P=0.01 and anterolateral, P<0.001). There was no late gadolinium enhancement in any of the participants before or post HI(I) T. Conclusions-Sixteen weeks of HI(I) T lead to measurable changes in cardiac atrial and ventricular morphology and function in previously untrained men. This correlates with improvements in parameters of endurance capacity.