Letter by Iellamo and Volterrani Regarding Article, “High-Intensity Interval Training in Patients With Heart Failure With Reduced Ejection Fraction”
Authors: Ferdinando Iellamo, Maurizio Volterrani
Journal: Circulation (2017)

It is with great interest the we read about the SMARTEX Heart Failure Study (Study of Myocardial Recovery After Exercise Training in Heart Failure), 1 which compared the effects of high-intensity interval training (HIIT) and moderate continuous training (MCT) in reversing left ventricular remodeling and increasing aerobic capacity in patients with heart failure and depressed systolic function.The SMARTEX Study 1 challenges the early findings by Wisløff et al 2 on the superior benefits of HIIT over MCT in chronic heart failure and confirms, on a larger scale, the results from our 3,4 and other laboratories 5 suggesting that HIIT is equally as effective as MCT in improving aerobic capacity and other risk factors.Findings from SMARTEX prompted some considerations that we wish to bring to the attention of the readers.In the study by Wisløff et al, 2 HIIT and MCT were matched by equating energy expenditure between the training modes.With this approach, actual training load was greater in the HIIT group than the MCT group. 3ndeed, when training load has been closely matched, no significant differences between HIIT and MCT have been detected in aerobic capacity, hemodynamics, ejection fraction, and lipid profile, 3 as well as in the improvement of cardiac autonomic regulation, 4 a major negative prognostic indicator, in patients with chronic heart failure.To quantify the training load, we used the training impulses (TRIMP) method to provide equivalent doses of exercise in both HIIT and MCT.The TRIMP method takes into account not only the energy expenditure (ie, the external load) but also the internal, metabolic, load.This is assessed on the basis of the exponential relationship that exists between the rise of blood lactate levels and the elevation of exercise heart rate (HR) above resting HR and allows us to account, in a single term, for both the intensity and volume of a training session.It should be noted that aerobic training prescriptions based on Vo 2 max or HR percentages may result in different physiological responses, even in patients with similar baseline aerobic capacities.These differences in exercise responses might be the consequence of differences in individual internal training load resulting from a broad intersubject variability in lactate response in individuals with similar aerobic capacity, even while exercising at the same percentage of maximum oxygen consumption (Vo 2 max).Hence, prescription of endurance training should not be based solely on percentages of Vo 2 max or HRmax (or HR reserve) when a comparable metabolic load is intended.The TRIMP concept fits well with the suggestion of the SMARTEX investigators 1 that training load should be regularly adapted to improvement in exercise capacity.TRIMP enables accurate weekly training load adjustments within both continuous and interval training modes. 3,4It is not based solely on preintervention criteria (eg, Vo 2 max or HRmax) that are not updated during the training process, thus account-