# Body Height Trajectories in Pediatric Competitive Athletes from 46 Different Sport Types
## 4 Discussion  
The aim of this study was to examine height changes in pediatric competitive athletes from 46 different sports who were followed over several years. The main finding was that height SDS did not change significantly throughout the follow-up period in the group as a whole and also when examined in subgroups of males only, females only or participants with different first measurement ages at the clinic. However, in endurance athletes that continuously trained in swimming, cycling and triathlon, height SDS decreased with time by a degree corresponding to approximately 1-2 cm/year. The decrease in height SDS trajectories in the endurance athletes in our study can perhaps be explained by the higher energy expenditure in their training sessions as compared to ball games and gymnastics. The youth compendium of physical activities [15] lists the energy expenditure of swimming at ~9-10 METs, cycling at fast speeds at 6.5-8 METs and fast running at ~8-13 METs. In comparison, lower energy expenditure is listed in the sport types where no decrease in height SDS was seen, namely, basketball (~5-7 METs), football (5.5-8.7 METs), tennis (6.3-6.7 METs) and gymnastics (2.7 METs). Per unit of activity, higher energy is, hence, expended in endurance sports compared with ball games and gymnastics. In addition, training sessions in these latter sport types also contain skill practice that is of a much lower intensity than actual play. The total energy expenditure of a training session will, therefore, be much lower than the METs listed above. For example, studies have shown that only ~50% of practice time in male youth ball games contained moderate-intensity physical activity [16; 17]. In comparison, running, cycling and swimming are typically performed throughout most of the training sessions in these sport types. Finally, the volume of training in endurance sports is also very high; in one study, for example, adolescent competitive swimmers trained for a minimum of five days per week, with a minimum of 130 min per session [18]. In a recent statement on youth running, it was summarized that youth runners often do not meet their energy needs, placing them at risk for low energy availability [19]. It is, therefore, plausible that the high energy needs and turnover of pediatric endurance athletes might negatively affect their height gain, as found in this study. This novel finding should nonetheless be verified in additional studies that will formally measure energy intake, expenditure and turnover, while addressing sexual maturation, sex differences and biological age. Regarding the other sport types examined in this study, our findings corroborate the existing literature on female gymnasts and dancers: that their heights are not compromised by intensive training [9; 12]. We acknowledge that our study had several limitations. We did not have height measurements taken before sports training commenced, and we did not have data regarding training intensities. However, the first years of sports practice are usually not very intense from an energy expenditure perspective and, hence, are not expected to influence growth.