Response to Letters Regarding Article, “Can Intensive Exercise Harm the Heart? You Can Get Too Much of a Good Thing”

Abstract

We thank our colleagues for their interest in our article pertaining to the controversial topic of whether intense exercise can cause cardiac injury.1 Drs Scott and Haykowsky argue that we did not adequately address exercise dose as defined by both duration and intensity. We believe that this critique may be reasonably leveled at the entire field of exercise cardiology in which there is no standard definition of what constitutes an athlete, intense exercise, or endurance exercise. For example, we have previously noted that the definition of intense exercise used in the cardiology literature (10 metabolic equivalents or 35 mL·min −1 ·kg −1 oxygen utilization) would be regarded as a warm-up for many competitive athletes.2 This has led to considerable confusion in discussions of the health benefits of high-level exercise. Until we devise some standard reference of exercise quantification, we will continue to lump recreational exercise enthusiasts and professional athletes under nonspecific umbrella terms when the amount of exercise, extent of cardiac remodeling, and related health consequences may be quite different. In the words of Paracelsus referred to by Scott and Haykowsky, we cannot attempt to discriminate between the "the right dose [which] differentiates a poison and a remedy" if we do not even know how to measure the dose. We would support a peer group discussion aimed at establishing clearer definitions of exercise quantification so that we can approach this expanding field of scientific discovery with greater clarity.Dr Möhlenkamp and colleagues highlight another interaction between intense exercise and cardiac health that we did not address. We thank them for highlighting the fact that intense exercise can serve as a trigger of cardiac events in persons with underlying atherosclerotic coronary disease. In our article, 1 we discussed the controversial and unproven causal relationship between exercise-induced cardiac remodeling and predisposition to arrhythmias such as atrial fibrillation and ventricular arrhythmias. As a very important but different clinical question, Möhlenkamp et al investigated subclinical coronary vessel disease in middle-aged exercise enthusiasts who had relatively recently taken up marathon running. They studied 108 subjects who were >50 years of age (mean age, 57 years) and had started marathon training within the preceding decade.3 More than half of the subjects were previous smokers, their body mass indexes were in the upper end of the healthy range, and their exercise training volume was relatively modest compared with that proposed to cause cardiac remodeling. Therefore, it was perhaps not surprising that Möhlenkamp et al identified an incidence of coronary vessel disease approximating that of the general population. For reasons that remain unexplained, they also found more prevalent myocardial fibrosis. Their study design does not address the causal question, that is, whether intense exercise prevents or promotes atherosclerotic heart disease. This would require a study of in...

The acute impact of an ultramarathon on right heart: A 12‐lead ECG study

“…The benefits of moderate exercise are indisputable, and physical activity should be encouraged in all individuals including those with chronic cardiac disease. However, although the analysis of the cardiovascular consequences of different intensity of endurance exercise was beyond the scope of the present study, the discrepancies found among the arrhythmic effects of different endurance disciplines may support the theory that more extreme endurance exercise may be associated with an excess of arrhythmias contrary to the plethora of beneficial effects offered by moderate endurance training …”

“…However, although the analysis of the cardiovascular consequences of different intensity of endurance exercise was beyond the scope of the present study, the discrepancies found among the arrhythmic effects of different endurance disciplines may support the theory that more extreme endurance exercise may be associated with an excess of arrhythmias contrary to the plethora of beneficial effects offered by moderate endurance training. 34,35 Finally, in our study we also observed greater T-wave amplitude at the finish-line evaluation as compared with ECG data collected the day before the competition, in absence of relevant differences between men and women. 36 During exercise T-wave magnitude tends to lessen, showing a marked increase in the first minutes of recovery.…”

Echocardiographic measurements of right heart size and function in healthy horses

“…Left ventricular (LV) size and function have been described in detail using two-dimensional (2D), M-mode, pulsed wave (PW) Doppler and more recently tissue Doppler imaging (TDI) and twodimensional speckle tracking (2DST) measurements [1][2][3][4][5][6]. Recent evidence also suggests that, in man, training has a pronounced impact on RV structure and function due to the disproportionate rise in pulmonary artery pressure during exercise [8]. Recent evidence also suggests that, in man, training has a pronounced impact on RV structure and function due to the disproportionate rise in pulmonary artery pressure during exercise [8].…”

Author response

“…However, significant RV enlargement and reduced RV reformation has been documented in much larger cohorts of young elite athletes 2. Not all athletes are equal,3 and these seemingly incongruent results might be explained by the fact that the athletes in the Teske's study were performing 4–5 times the amount of weekly training. There are many more studies than these, and we agree that there is evidence to both support and refute the idea of permanent cardiac remodelling of the RV, left ventricle (LV) and the atria.…”

“…Our analysis suggests that this may be missing the point. A syndrome of proarrhythmic remodelling of the RV which seems to be associated with long-term endurance exercise training has been described in humans3 4 and in rats 5. We believe that it would be incorrect as clinicians and scientists to not at least entertain the possibility that high-intensity endurance exercise may be associated with these potentially life-threatening conditions.…”