Various aspects of upper-limb muscle strength and tennis performance: A comparative study of U12 and U14 female tennis players

This study investigated the relationship between muscle strength and tennis performance, assessed using the International Tennis Number (ITN) protocol, in young female tennis players aged under 12 (U12) and under 14 (U14). Thirty-three players underwent a comprehensive evaluation including ITN testing, general strength tests (handgrip strength, flexed arm hang, and tennis-ball throw), isometric upper-limb muscle strength, and sense of force assessment. Results demonstrated significantly higher ITN scores and muscle strength in the U14 group, with differences largely attributable to body size and training experience. Correlation analyses revealed age-specific patterns: in U12 players, ITN scores were associated primarily with general strength measures, whereas in U14 players, they were more strongly linked to joint-specific upper-limb strength and neuromuscular characteristics. Sense of force did not differ between groups, though correlations with ITN varied depending on age and joint function. These findings suggest that, in this sample, performance in younger players was more closely associated with general strength measures, whereas in older players it was more closely associated with joint-specific upper-limb strength, underscoring the importance of adjusting training strategies to both the biological and technical stages of athletes. The results highlight the role of muscle strength not only in supporting general performance but also in refining technical execution in young female tennis players.