BLUNTED GROWTH VELOCITY IN FEMALE ARTISTIC GYMNASTS

Abstract

Dear Editor-in-Chief: We believe that the comments by Beunen, Malina, and Baxter-Jones (1) regarding our manuscript on growth in young gymnasts are based on misinterpretation of the methodology and the data presented in our manuscript (2). Our conclusions are indeed supported by the data. First, to highlight that only 6 advanced and 16 intermediate-level gymnasts were followed for 24 months is misleading (and inaccurate) given that we followed 72 advanced and 65 intermediate-level female gymnasts for varying periods ranging from 6 to 24 months. Second, we wish to clarify that we did not attempt to construct individual growth curves to describe the adolescent growth spurt in the gymnasts-the Preece-Baines growth model (PBGM) was simply used to estimate age at peak height velocity (PHV) and PHV. We agree with Beunen et al. that there are several limitations associated with the use of this model for estimating age at PHV and PHV from cross-sectional data. However, in our study the PBGM was fitted to the mixed-longitudinal mean stature of the gymnasts-not cross-sectional mean heights as indicated by Beunen and colleagues. Notably, Malina and colleagues apparently agree that these limitations are acceptable given that they used a similar approach in a recent publication (3). In this paper, they stated: "Although the application of the Preece-Baines model to cross-sectional means has limitations, it provides an estimate of the timing of maximum velocity of adolescent growth in height (age of PHV) for comparative purposes" (p. 169). Third, we wish to highlight that the PBGM was just one approach that was used to address the main aims of our study. For example, using robust standard error regression analysis we reported that there was no marked acceleration in height and sitting height velocity during puberty for the advanced gymnasts. We also found that growth for the pre- and peripubertal gymnasts deviated from the 50th toward the 25th to the 5th percentile with advancing age. Furthermore, inspection of individual growth rates revealed a high frequency of growth faltering (height velocity < 4.5 cm·yr−1) in the pre- and peripubertal gymnasts. To simply dismiss our conclusions based on the PBGM indicates they failed to consider (or chose to ignore) all the available evidence presented in our paper. Beunen et al. concluded that "inaccurate results and conclusions based on in appropriate analyses do not advance our knowledge in this domain of the exercise and sport sciences." We acknowledged that there were several limitations with our study (p. 1058), but maintain that the most appropriate analyses were conducted to address the research questions. To apparently ignore all of the evidence presented in our manuscript is misleading and restricts the progress in this field in terms of gaining a greater understanding about the potential influence of intense training on the growth of young athletic children. Finally, we maintain that our choice of such phrases as "adversely affected" or "blunted" does not point to biased interpretation. In fact, we acknowledge on page 1058 that the blunting of the growth spurt is an acknowledged characteristic of short-term mixed-longitudinal data. We provide several levels of evidence that support the notion that in some, but not all young female gymnasts, participation in competitive gymnastics may alter the timing and tempo of growth. Robin M. Daly Shona L. Bass Centre for Physical Activity and Nutrition Research School of Exercise and Nutrition Sciences Deakin University Melbourne, Australia Dennis Caine Department of Physical Education, Health and Recreation Western Washington University Bellingham, WA