Running Economy in 9- to 17-Year-Old Soccer Players

Abstract

Running economy (ml.kg−1.min−1) seems to improve steadily with age, both in normally active children and adolescents and in those subjected to formal training. Allometric modelling for body mass, on the other hand, provides evidence of lack of effects for maturity in submaximal VO2 uptake. PURPOSE: The purpose of this study was to investigate the influence of treadmill gradient and velocity on the relationship between maturation and running economy. We hypothesized that a smaller increase in the oxygen uptake with increasing slope in younger children would indicate that they are less economical because of body dimensions. METHODS: Forty 9 to 17-year-old soccer players participated in this study. Standard anthropometric measurements as well as skeletal age (SkA), based on radiographs of the hand and wrist bones acording to Tanner-Whitehouse III Method (TW3) were assessed. Running economy was evaluated during a submaximal test protocol with three 6 min workloads with fixed velocity and gradient: the first at 8 km/h and 0% (EC8/0), the second at 9,5 km/h and 0% (EC9.5/0) and the third at 8 km/h and 5% (EC8/5). After cluster analysis, the whole sample was divided in three groups with the SkA as criterium: Group 1 <12years; Group 2≥12, <14years; Group 3 ≥14years. Correlation coefficients between variables were calculated using Pearson's Product Moment (r). The interaction between SkA groups and workloads was analysed using two-way ANOVA with repeated measures. RESULTS: VO2 uptake (ml.kg−1.min−1) consistently decreased with body mass increment for the three submaximal workloads (p<0.05 in EC8/0 and EC8/5; p<0.01 in EC9.5/0) but was not related to SkA in any situation. Standard ratio VO2 values were negatively correlated to body mass (p<0.05) in all workloads but were not significantly different among groups, in any workload. Percent differences in VO2(ml.kg−1.min−1) from EC8/0 to EC8/5 and to EC9.5/0 were correlated (r = 0.564; p<0.01) in the whole sample but were not significantly different from each other neither did they vary between SkA based groups. Allometric modelling provided us with scaling factors of 0.838, 0.843 and 0.842 for EC8/0, EC8/5 andEC9.5/0, respectively. VO2 scaled allometric ally showed stables values with SkA (r = 0.02). CONCLUSIONS: Within this group of young soccer players, submaximal VO2 responses were explained predominantly by changes in body mass, with no additional maturity-related effects. Moreover, the variation in oxygen uptake as a consequence of increased workload either by velocity or slope increases is independent of maturation.