LETTER TO THE EDITOR
Definition of physiological hypertrophy in ultramarathon athletes
Gillian A. Whalley, MHSc, DMUa and
Robert N. Doughty, MD, MRCP, FRACPa
a Cardiovascular Research Laboratory, Department of Medicine, University of Auckland, Private Bag 92 019, Auckland, New Zealand
g.whalley{at}auckland.ac.nz
We read with interest the study by Nagashima et al. (1) regarding significant cardiac dilation and adaptation in ultradistance runners. The investigators report large aortic, left atrial, and left ventricular (LV) dimensions in 291 male ultramarathon runners and found weak relationships between heart size and body surface area (BSA) and significant relationships with the extent of training. It is not surprising that heart size had only a weak relationship with BSA; although heart size is related to body size, lean body mass is the only predictor of LV mass in adults (2) and is an important predictor of both cardiac output and stroke volume (3).
Several studies have compared heart size as measured by echocardiography between athletes and control subjects and reported both LV hypertrophy and dilation in athletes. Some studies have used BSA to index echocardiographic measurements, but none has used lean body mass. This is particularly important because both endurance (4) and resistance training (5) induce increases in muscle size and thus lean body mass.
It is usual, and indeed necessary, to index echocardiographic measurements to body size in order to compare individuals of different body size. This can be particularly important when changes in body composition may be anticipated due to a pathological process or lifestyle change. It is common for echocardiographic measurements to be indexed to BSA (estimated from height and weight measurements) in order to compare heart size between different-size individuals and to establish normal ranges for detection of pathological LV hypertrophy. However, because BSA is affected by fat mass, and fat mass neither correlates with nor predicts LV mass (2), this method may overestimate the degree of LV hypertrophy in lean subjects. Although lean body mass would appear to be the optimal indexation measure, it is rarely used, because accurate measurements are not widely available and substitute methods, such as skin-fold thickness measurements, are relatively inaccurate. Height raised to various integers also correlates with LV size and are now widely recommended in place of BSA (6).
Echocardiography is performed in athletes primarily to determine pathological changes that might occur as a result of extensive training. The physiological adaptations observed in athletes are related to both the hemodynamic affects of exercise and overall body effects, including increased lean body mass. However, using unindexed measurements, as in the study by Nagashima et al. (1), or indeed measurements that are indexed to inappropriate body size measures, may lead to misleading conclusions and does not aid differentiation of pathological from physiological adaptation.
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1. Nagashima J, Musha H, Takada H, Murayama M. New upper limit of physiologic cardiac hypertrophy in Japanese participants in the 100-km ultramarathon. J Am Coll Cardiol. 2003;42:1617–1623[Abstract/Free Full Text]
2. Whalley GA, Gamble GD, Doughty RN, et al. Left ventricular mass correlates with fat-free mass but not fat mass in adults. J Hypertens. 1999;17:569–574[CrossRef][Medline]
3. Collis T, Devereux RB, Roman MJ, et al. Relations of stroke volume and cardiac output to body composition: the Strong Heart Study. Circulation. 2001;103:820–825[Abstract/Free Full Text]
4. Gollnick P, Armstrong R, Saubert C, Piehl K, Saltin B. Enzyme activity and fiber composition in sekeltal muscle of untrained and trained men. J Appl Physiol. 1972;33:312–319[Free Full Text]
5. MacDougall J, Sale D, Moroz J, Elder G, Sutton J, Howald H. Mitochondrial volume density in human skeletal muscle following heavy resistance training. Med Sci Sports Exerc. 1979;11:164–166
6. de Simone G, Verdecchia P, Schillaci G, Devereux RB. Clinical impact of various geometric models for calculation of echocardiographic left ventricular mass. J Hypertens. 1998;16:1207–1214[Medline]
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