Allometric analysis of the association between cardiac dimensions and body size variables in 464 junior athletes

Abstract

Empirically derived relationships between body size variables and cardiac dimensions have not been published previously for a large sample of male and female athletes. This process would inform scaling practice and facilitate intra- and inter-group comparisons of cardiac data. Therefore we investigated the relationships of body mass (BM), height and body surface area (BS) with a range of cardiac dimensions derived by echocardiography in 464 male and female elite junior athletes (age range 14-18 years; sporting allocation included rowers, cyclists, footballers, tennis players, swimmers and a miscellaneous group). Initial linearity checks suggested that most of the relationships between the body size variables and cardiac dimensions were non-linear, thus precluding the simple ratio standard approach to scaling. Multiple log-log least-squares linear regression confirmed commonality of slopes (between males and females, across the age range and between sporting groups) for all relationships involving BM and BS. Subsequent analyses of the slope exponent (b) for left ventricular dimensions supported previous data and were dimensionally consistent (LVM-BM, b=0.91+/-0.11; LVM-BS, b=1.44+/-0.19; where LVM is left ventricular mass), except for left ventricular internal dimension in diastole (LVIDd) (LVIDd-BM, b=0.25+/-0.04). Data for the left atria internal dimension (LA) were also dimensionally consistent (LA-BM, b=0.29+/-0.09); however, this was not the case for the right ventricular internal dimension in diastole (RVIDd) (RVIDd-BM, b=0.76+/-0.14). It is possible that these results were due to a study-specific limitation in the data range (LVIDd) and the geometric peculiarities of RVIDd compared with LVIDd. The gender/age/sporting groupxbody size interaction factor for virtually all relationships between height and cardiac dimensions was significant (P<0.05), and thus whole-group b exponents could not be generated. Generally these data support previous small-sample research with athletes, and suggest that allometric scaling, as opposed to simple ratio scaling, should be adopted in studies of cardiac dimensions in athletes. This should allow, with minimal mathematical difficulty, the production of body-size-independent cardiac indices to be evaluated in laboratory or clinical work. Further research is required to develop normative 'allometrically derived' cardiac indices, and care should be taken to determine relationships in specific population groups as well as to confirm commonality of slopes in multiple group comparisons. Caution is expressed regarding the use of height as a scaling variable in future research.

Derivation of a Size-Independent Variable for Scaling of Cardiac Dimensions in a Normal Adult Population

“…Although most cardiac studies rely on linear scaling for correction or normalization, few if any authors check to see whether the normalization process actually removes the correlation of their scaled data with the size variable used for scaling, or indeed, other measures of body size. 3,11,12 Our data indicate that, in all cases, linear scaling actually increases the correlation that the operation seeks to remove and confirms prior observations indicating that allometric rather than linear scaling best corrects for body size. 3,11,12 The superiority of an allometric model is consistent with the observation that physiologic variables in general bear an exponential relationship to body size.…”

“…3,11,12 Our data indicate that, in all cases, linear scaling actually increases the correlation that the operation seeks to remove and confirms prior observations indicating that allometric rather than linear scaling best corrects for body size. 3,11,12 The superiority of an allometric model is consistent with the observation that physiologic variables in general bear an exponential relationship to body size. It is also consistent with the theory of geometric similarity, which holds that a linear dimension such as the LAD should be geometrically related to the square root of a twodimensional measure such as BSA and the cube root of a threedimensional measure such as BW.…”

“…Similarly, a study of 464 junior athletes did not find HT to be "an appropriate scaling variable" because of the limited range of HT even in this relatively large cohort of growing adolescents. 11 Likewise, Lauer et al 3 found a minimal relationship between HT and LAD in adults. BSA, like HT, is also frequently used to index cardiac variables.…”

The upper limit of physiological cardiac hypertrophy in elite male and female athletes: the British experience

“…The use of per ratio standard scaling for anthropometric characteristics has been criticised (Batterham et al 1999). Recent evidence suggests that allometric scaling offers a more meaningful comparison of left ventricular structure (George et al 2001). In the present study a range of body sizes were observed in those athletes presenting with a maximum wall thickness ‡13 mm, suggesting that additional factors, including genetics, may underpin the adaptive response of the left ventricle to a chronic exercise stimulus.…”

Allometric scaling for left ventricular mass and geometry in male and female athletes of mixed and endurance sports

“…Giraldeau et al presented a collegiate athlete population and demonstrated that sex differences in absolute and ratiometrically scaled LVM were eliminated when allometrically scaled to lean body mass [ 29 ]. Whilst in a cohort of 464 junior athletes, it was found that size independence of LVM was achieved by scaling allometrically to BSA but with a different exponent (b = 1.5) than derived from our data [ 30 ]. This may be related to the wide-age range of our population, reflecting the interaction of both age and athletic adaptation on LVM.…”