505 The magnitude of 505 change of direction (COD) asymmetry decreases with chronological age in male and female youth elite tennis players: Results from 11 years of follow-up.

Introduction: Functional asymmetry can exacerbate by practicing unilateral sports, such as tennis, and has been associated with impaired athletic performance. This longitudinal study investigated the development of 505 COD asymmetry in youth elite tennis players.
Methods: Using an 11-year longitudinal cohort study design, the development of COD asymmetry was yearly assessed in 323 male and 235 female youth elite tennis players (aged 6-13 years). Their 505 COD performance (i.e., time to cover 5m, turn 180° and sprint 5m back) was recorded three times for both directions of rotation. The magnitude of functional asymmetry was calculated using the dominant (i.e., overall best result) and non-dominant value (i.e., best test result of the opposite direction): ([dominant value–non-dominant value]/dominant value)*100. Linear mixed effects regression models were used to examine the development of both performance and asymmetry in the 505 COD test according to players’ chronological age and sex. Kappa coefficients examined the consistency regarding the direction of asymmetry across test occasions.
Results: Regardless of sex, 505 COD performance significantly improved (i.e., less time needed to complete the test) with increasing chronological age (p<0.001). An increase in players’ chronological age was also related to a significant decrease in 505 COD asymmetry magnitude (-0.17±2.83% per year, p<0.001). Regardless of age, the male players showed a significantly lower 505 COD asymmetry magnitude compared to the female players (-0.30±1.00 %, p<0.001). The kappa coefficients were poor to slight (0.00-0.02) for all youth elite tennis players.
Conclusion: Although the yearly 505 COD performances significantly improved with growing older, the magnitude of 505 COD asymmetry – which was found to be higher in boys – significantly decreased in youth elite tennis players according to their chronological age. The large standard deviations and the poor to slight kappa values, however, emphasize the need for an individual and time dependent approach when monitoring 505 COD asymmetry.