(12) Longitudinal Analysis of Inter-Limb Asymmetry Indexes and Vertical Jump Performance in Elite Wushu Athletes

The study of inter-limb asymmetry is crucial in understanding athletes' performance. However, limitations in the existing research, such as the lack of longitudinal data and failure to account for individual athlete variability, hinder a comprehensive understanding of this phenomenon.

Purpose: To examine the longitudinal changes in interlimb asymmetries, their effect on jump performance, and how different asymmetry calculations affect these changes and impact on performance.

Methods: A retrospective analysis of 17 elite level Wushu martial arts athletes (Females=8; Males=9) was conducted. For each week of regular training, athletes performed 3 countermovement jumps with hands akimbo on two uniaxial force platforms (1,000Hz) with self-selected rest between trials. A total of 76 weeks and 3096 trials were used for statistical analysis. Vertical jump height (JH) was estimated using the impulse-momentum method. Four interlimb asymmetry indexes were calculated: Index 1=(A-B)/max(A,B)*100, Index 2=(A-B)/(A+B)*100,  Index 3=(45-arctan(A/B))/90*100, and Index 4=ln(B/A)*100 to determine differences among asymmetry calculation methods. Data was analyzed using a series of independent linear mixed models, in which a triple interaction of fixed effects was performed to account for time (week), asymmetry index, and sex (male|female), while accounting for any individual variations at baseline (intercept) and any changes of the center of mass (depth_COM) for each jump within each session across all of testing sessions. Statistical significance was set at p< 0.05. RESULTS: JH significantly increased over time (Estimate = 0.016, p = 0.002), indicating a positive training effect. Regarding the four asymmetry indexes, while the main effects of these asymmetry indexes on JH  were not statistically significant, their interactions with sex demonstrated noteworthy associations, specifically in male athletes. Specifically, the interaction terms between these indexes and sex revealed significant positive associations in male athletes, suggesting that asymmetry indexes may have differential effects on JH in male individuals. For instance, for index 2, the interaction with time (week) and Index 2 suggests that for each unit increase in time (week) and asymmetry index 2 in male athletes, there is an estimated decrease in JH of approximately 0.005 cm.  Similarly, for index 3, the interaction with time (week*Index) suggests that for each unit increase in time (week) and Index 3, there is an estimated decrease in JH of approximately 0.008 cm among male athletes.

Conclusions: Overall, these results suggest that the relationship between Index 2 and Index 3 with JH varies depending on the interaction with sex and time. PRACTICAL APPLICATIONS: Athletes and Coaches should pay attention to how interlimb asymmetry indexes are calculated and special consideration should be given to these changes over time, particularly in male athletes.

Acknowledgements: We would like to thank the Wushu athletes from the Malaysia Team and Staff members