Height, mass and skeletal maturity (Fels method) were assessed in 135 elite youth soccer players aged 10.7-16.5 years (only two boys were < 11.0 years). Sample sizes, years of training and current weekly training volume by two-year age groups were: 11-12 years (n = 63), 2.6 +/- 1.0 years and 4.1 +/- 1.7 h; 13-14 years (n = 29), 3.1 +/- 1.6 years and 4.5 +/- 1.7 h; 15-16 years (n = 43), 4.7 +/- 2.4 years and 6.1 +/- 2.0 h. The oldest age group included members of the national youth team. Heights and masses were compared to US reference values, and skeletal age and chronological age were contrasted. The players were also classified as late, average ('on time') and early maturers on the basis of differences between skeletal and chronological age, with the average category including boys with skeletal ages within +/- 1 year of chronological age. The mean heights and masses of 11- to 12-year-old soccer players equalled the US reference values, while those of players aged 13-14 and 15-16 years were slightly above the reference values. The mean skeletal age approximated mean chronological age in players aged 11-12 years (12.4 +/- 1.3 and 12.3 +/- 0.5 years, respectively), while mean skeletal age was in advance of mean chronological age in the two older groups (14.3 +/- 1.2 and 13.6 +/- 0.7 years, respectively, in 13- to 14-year-olds; 16.7 +/- 1.0 and 15.8 +/- 0.4 years, respectively, in 15- to 16-year-olds). Seven boys in the oldest age group were already skeletally mature and were not included when calculating differences between skeletal and chronological age. The proportion of late maturing boys in this sample of elite soccer players decreased with increasing chronological age. Among 11- to 12-year-old players, the percentages of late and early maturing boys were equal at 21% (n = 13). Among 13- to 14-year-old players, the percentages of late and early maturing boys were 7% (n = 2) and 38% (n = 11) respectively, while among players aged 15-16 years the percentages of late and early maturing boys were 2% (n = 1) and 65% (n = 28) respectively. The results of this comparative analysis suggest that the sport of soccer systematically excludes late maturing boys and favours average and early maturing boys as chronological age and sport specialization increase. It is also possible that late maturing boys selectively drop-out of soccer as age and sport specialization increase.

Two asthma phenotypes were identified in elite athletes: "atopic asthma" and "sports asthma". The type of sport practiced was associated with different phenotypes: water and winter sport athletes had three- and ninefold increased risk of "sports asthma". Recognizing different phenotypes is clinically relevant as it would lead to distinct targeted treatments.

Among adolescent soccer player, boys advanced in SA for CA are overrepresented and those later in SA for CA are underrepresented with increasing CA. If Fels SA was used to verify CA in this sample of youth for under-17 competition, 36 skeletally mature players aged 15 to 17 years (16%) would be disqualified. The results for this sample of male soccer players question the utility of SA or magnetic resonance imaging as a valid estimate of CA in youth sport competitions.