“Do fast players remain fast and slow players remain slow?” Long-term development of maximal sprinting speed in highly trained U12 to U19 soccer players over an 8-year period

The aims of this study were to investigate MSS development in highly trained male U12 to U19 soccer players by i) describing the absolute maximal sprinting speed (MSS) by age group, ii) assessing changes in players’ relative MSS development across consecutive age groups, and iii) analysing the long-term stability of MSS over an 8-year period. Using a mixed-longitudinal design, we collected data from 475 players (n = 1042 datapoints). MSS was determined from the average velocity in the 20-30 m interval of a 30 m linear sprint. Percentile values were assigned to every MSS and players were classified into six performance groups based on their percentile value. The number of players moving up, down, or remaining in the same performance group across consecutive age groups was calculated. Intraclass correlation coefficients (ICC; 3,1) were computed to assess the long-term stability. MSS improved consistently from U12 to U19, with the greatest improvements observed between the U14 to U16. Overall, more players transitioned to a slower performance group (41%) than remained in the same (34%) or moved to a faster group (25%) across consecutive age groups. Long-term stability of players’ percentile values was moderate between consecutive age groups (ICCs 0.61 to 0.79) and the entire sample (ICC = 0.65, 95% CI (0.57 to 0.73)). Our findings highlight the general stability of MSS performance throughout adolescence, although they challenge the general notion that fast players always remain fast and slow players always remain slow. This information helps coaches to appropriately interpret current and potential future sprint performance for talent evaluation and selection purposes in soccer.