Change of Direction Asymmetry in Youth Elite Tennis Players: A Longitudinal Study

Longitudinal investigations into the development of inter-limb
asymmetry in sports are scarce. This study examined the development of change of direction (COD) asymmetry magnitude
in youth elite tennis players. Dominant (overall best performance) and non-dominant (best performance on the other
side) scores and COD asymmetry magnitude were quantified
annually (up to six years) in 323 male and 235 female players
(ages 6 to13 years). Linear mixed effects regression models
examined the development of COD performance and asymmetry magnitude according to players’ chronological age and
sex. Kappa coefficients examined the consistency for the direction of asymmetry across test occasions. Regardless of sex,
COD performance significantly improved (p<0.001) while COD
asymmetry magnitude significantly decreased (−0.17±0.87%
/ year) with increasing chronological age. Regardless of age,
males showed significantly lower COD times (−0.111±0.091s)
and lower COD asymmetry magnitude (− 0.30 ± 1.00%) compared to females. The slight and poor (k-value = 0.02–0.00)
kappa coefficients for males and females, respectively, highlight the direction specificity of functional asymmetry. These
data show that whereas performance of the COD test improved, the magnitude of COD asymmetry declined across
chronological age in youth tennis players.