Isokinetic strength characteristics of trunk rotation and knee joint in female amateur boxers: asymmetry and implications for injury prevention

Objective: To investigate the asymmetry in trunk axial rotation and knee joint isokinetic strength characteristics among adolescent amateur female boxing athletes, providing guidance for sport-specific strength training and injury prevention. Methods: Sixteen adolescent amateur female boxing athletes [age 16.8 ± 1.8 years, height 168.2 ± 5.3 cm, body mass 59.7 ± 7.7 kg] were tested using the IsoMed 2000 isokinetic dynamometer. Knee joint concentric (CON) and eccentric (ECC) contractions, as well as trunk rotation concentric contractions, were assessed at angular velocities of 60°/s, 120°/s, and 180°/s, with 3 sets of 7 repetitions per velocity. Paired-samples t-tests were used to compare bilateral differences, and repeated-measures ANOVA was applied to evaluate velocity effects. Results: Trunk rotation concentric contractions exhibited significant velocity dependence and lateral asymmetry. Repeated-measures ANOVA revealed a significant main effect of velocity (P < 0.001). At 120°/s and 180°/s, left rotation (dominant side) showed significantly higher PT and TW compared to right rotation (P < 0.01, Cohen's d_z medium to large), whereas no significant difference was observed at the slower velocity of 60°/s. Knee joint eccentric strength was significantly greater than concentric strength (P < 0.001). In ECC mode, right-side flexor group PT and TW were significantly higher than the left side (P < 0.01), with a significant main effect of velocity (P < 0.001). In CON mode, parameters peaked at 60°/s and decreased significantly with increasing velocity (P < 0.001). The hamstring-to-quadriceps (H/Q) ratio showed no significant bilateral differences in CON mode (P > 0.05), but in ECC mode, the left side was significantly higher than the right (P < 0.01), with the asymmetry magnifying as velocity increased. Conclusion: Adolescent amateur female boxing athletes demonstrate significant asymmetries in trunk rotation (left > right) and knee joint muscle strength (ECC right flexors > left), with stronger performance on the dominant side. These imbalances may elevate the risk of lumbar and knee injuries. Compared with similar studies on amateur boxers, lower limb absolute strength appears relatively low in the present cohort. It is recommended to implement balanced bilateral trunk rotational training, strengthen rapid force production in the non-dominant side, and optimize the H/Q ratio to enhance sport-specific performance and reduce injury risk.