Upper extremity bone mineral content asymmetries in tennis players: A systematic review and meta-analysis

The aim of this study was to examine the magnitude of upper extremity bone mineral content (BMC) asymmetries in tennis players. Furthermore, the influence of sex (male versus female versus mixed), chronological age (juniors: < 18 years; adults: 18-39 years and seniors: >= 40 years) and starting age (early starters: 18 years) on these asymmetries were examined. Two databases were searched for scientific articles that examined upper extremity BMC in tennis players. Pooling of the individual study effect sizes was conducted using the random-effects model. Three subgroup analyses were performed based on sex, chronological age and starting age. Out of the 15 included studies 24 effect sizes were extracted resulting in a significant difference in BMC value between the dominant and nondominant upper extremity of the tennis players (Standardised Mean Difference: 0.85 [95% CI: 0.67-1.03]). The three subgroup analyses all showed medium to strong effect sizes and significant intergroup differences. To conclude, BMC was significantly higher in the dominant upper extremity compared to the nondominant upper extremity in tennis players. Nevertheless, the influence of training volume and playing experience on these asymmetries are yet to be examined.