Training and activity level are important predictors of motor development. At present, many children and adolescents do not participate in any sport activity in their leisure time. In this investigation, we analyzed the level of performance of the stretch and shortening cycle (SSC) in childhood and youth. Data of 801 participants were recorded for 2 separate groups, those in elite soccer associations and those who were less active in their leisure time. All the participants completed the following performance tests: the squat jump, the countermovement jump and the drop jump from varying heights. All the participants answered a questionnaire to determine their level of activity. Comparisons of performance were made across the 2 groups. The data showed a significant (p < 0.05) advantage for soccer players in nearly every variable involved in the performance of the SSC. The analysis of the questionnaire highlights the fact that approximately a quarter of students are inactive in their leisure time, which means they do not participate in any sport activity except for school sports. The data show that many children and adolescents do not participate in sport activities in their leisure time. Furthermore, many of these children and adolescents have a body mass index >25. The results of this investigation support the fact that inactivity is correlated with a low training level in children and youth.