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Jožef Šimenko and Vedran Hadžić

Purpose: This study investigates bilateral performance with the Special Judo Fitness Test (SJFT) and its associations with competition performance (CP) and competition volume (CV) in judo. Methods: The SJFT compared movement patterns of the dominant (D) and nondominant (ND) sides on a sample of 27 youth judoka. Repeated-measures analysis of variance was used to determine differences in SJFT execution to the D and ND side, and for associations, the Pearson correlation was used (P < .05). Results: The total number of throws is significantly higher on the D side, with better performance in the final SJFT index. The CP showed positive correlations with the D side of SJFT executions in the second part of SJFT (P = .042) and the total number of throws (P = .036). On the ND side, the CP showed a positive correlation with the second part of the SJFT (P = .014), a negative correlation with the third part of the SJFT (P = .035), and a positive correlation in the total number of throws (P = .027). CV shows significant correlations with all parameters of the SJFT in the D and ND sides, with stronger correlations on the ND side. Conclusions: The study presents significantly better performance in judokas’ D side in SJFT. Associations between CP and CV with the SJFT were significant in connection to both body sides. It highlights the importance of bilateral movement development and good execution of the throwing techniques for the D and ND body sides of youth judoka to achieve greater CP all year round.

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Darjan Spudić, Janez Vodičar, Miha Vodičar, and Vedran Hadžić

Context: The importance of isometric trunk strength (ITS) among sport science professionals is higher than its actual reported effect size on either performance or low back pain (LBP) occurrence. Objective: To provide normative values of ITS and strength ratios, and to evaluate the effect of sex, sports discipline, and LBP status. Design: Crossover study. Setting: University research laboratory. Participants: Five hundred and sixty-seven elite athletes (186 females) with and without a history of LBP from different sports. Main Outcome Measure: Participants underwent ITS testing for trunk flexors, extensors, and lateral flexors. Normalized maximal strength (in newton meter per kilogram) and strength ratios were calculated. Differences between sex, LBP, and sport disciplines were assessed with 3-way analysis of variance (sex × LBP status × 7 sport categories) and partial eta-squared (ηp2) effect size. The predictive validity of ITS for LBP was checked with receiver operating characteristics (area under the curve). Results: The authors found significant differences in extensor and flexor ITS in favor of male athletes (medium ηp2, P < .05), while sex differences in lateral flexion ITS had a low size effect (P < .05). A low size effect was also observed for the differences in strength ratios extensors/flexors (mean 1.47; 95% confidence interval, 1.45–1.50) and left flexors/right flexors (mean 0.99; 95% confidence interval, 0.98–1.01) among sexes. The sport discipline-related differences generally had a low size effect. No significant differences in ITS were found between LBP and LBP-free athletes. Only 50% to 58% of athletes (area under the curve, 0.501–0.582) were correctly classified as LBP or LBP-free using different ITS and strength ratio variables. Conclusions: ITS and strength ratios have low predictive validity for LBP history but may discriminate between sex and sport disciplines. Our data are a useful reference point for meaningful individual results interpretation when athletes are evaluated during training or rehabilitation.