This study aimed to examine side‐to‐side differences in phase angle (PhA) in both upper and lower limbs of youth elite tennis players. Among other outcomes, PhA was directly determined using segmental multifrequency bioelectrical impedance analysis (BIA) in 26 tennis players (11.6 ± 1.1 years, 54% boys) and compared against a sex‐ and age‐matched reference population. Significant upper limb asymmetry in PhA (p < 0.001), with a higher value on the dominant side of the body, was observed in the tennis players. At lower limb level, the tennis players showed a tendency towards a significantly higher PhA in the contralateral compared to the ipsilateral limb (p = 0.089). Using vector analysis (BIVA), a significant degree of PhA asymmetry (p = 0.002) was only reflected in the tennis players’ upper limb. Additional segmental outcomes also demonstrated a significant degree of upper limb asymmetry in terms of tennis players’ lean mass (p < 0.001), total segmental water (p < 0.001), fat mass (p < 0.001), extracellular water (p < 0.001) and extracellular water ratio (p < 0.001), whereas lower limb asymmetry was only observed in tennis players’ fat mass (p = 0.037) and extracellular water (p = 0.001). This is the first study to report significantly more pronounced BIA‐based side‐to‐side differences in youth elite tennis players compared to a non‐athletic reference population at the upper limb level, whereas no significant between‐group differences in the lower limbs were found. This explorative study should trigger future research to further scrutinize the role of BI(V)A as a promising field‐method in monitoring bodily asymmetries in youth elite tennis players in view of sport performance and athletic health.Highlights Bioelectrical Impedance Analysis is a promising field‐method to monitor side‐to‐side asymmetry in youth elite tennis players. Youth elite tennis players displayed a more pronounced degree of BIA‐based side‐to‐side differences compared to a non‐athletic reference population at the upper limb level, whereas whilst between‐group differences appeared to be less evident in the lower limbs. Future research is warranted to scrutinize whether and to what extent these degrees of segmental bodily asymmetry may be related to injury risk (prevention) and athletic development of (pre)adolescent tennis players.

Background: The presence of inter-limb asymmetry in the human body has traditionally been perceived to be detrimental for athletic performance. However, a systematic review addressing and comprehensively assessing the association of asymmetry between the lower limbs and middle- and long-distance running performance-related metrics is currently lacking. Objective: The main purpose of this systematic review was to examine the relationship between lower inter-limb asymmetry and determinants of running performance in healthy middle- and long-distance runners. The secondary objective was to identify possible avenues for further research in this area. Methods: PubMed, Web of Science and SPORTDiscus were systematically searched for studies investigating the relationship between lower inter-limb asymmetry and (determinants of) running performance in healthy and injury-free middle- and long-distance runners. The quality of studies eligible for inclusion was assessed using the Downs and Black Quality Index Tool. Results: Out of 4817 articles screened, 8 studies were included in this review which assessed the association between functional, morphological, kinematic and kinetic asymmetry and running performance-related metrics. The quality score of the included research varied between 5/10 and 9/10. Our results revealed mixed findings, showing both significant negative (n = 16) and positive (n = 1) associations as well as no significant associations (n = 30) between inter-limb asymmetry and running performance-related metrics. Conclusions: A high heterogeneity across study methods and outcomes was apparent, making it difficult to draw a straightforward conclusion. Our results indicate that the majority of metrics of functional, morphological, kinematic and kinetic inter-limb asymmetry are negatively or not associated with running performance (and/or its determinants). Thus, a more extensive high-quality body of research using standardised asymmetry magnitude metrics is essential to determine whether, and to what extent asymmetry between the lower limbs could affect middle- and long-distance running performance. Future studies should establish potential trade-off values to help practitioners develop evidence-based training programs. Key Points: In the majority of the metrics, the magnitude of lower inter-limb asymmetry was negatively or not associated with middle- and long-distance running performance. Coaches, athletes and researchers should be attentive of the task, time- and metric-specificity as well as the inter- and intra- individual variability of magnitude outcomes, when assessing inter-limb asymmetries.

Longitudinal investigations into the development of inter-limb asymmetry in sports are scarce. This study examined the development of change of direction (COD) asymmetry magnitude in youth elite tennis players. Dominant (overall best performance) and non-dominant (best performance on the other side) scores and COD asymmetry magnitude were quantified annually (up to six years) in 323 male and 235 female players (ages 6 to13 years). Linear mixed effects regression models examined the development of COD performance and asymmetry magnitude according to players’ chronological age and sex. Kappa coefficients examined the consistency for the direction of asymmetry across test occasions. Regardless of sex, COD performance significantly improved (p<0.001) while COD asymmetry magnitude significantly decreased (− 0.17±0.87% / year) with increasing chronological age. Regardless of age, males showed significantly lower COD times (− 0.111±0.091 s) and lower COD asymmetry magnitude (− 0.30±1.00%) compared to females. The slight and poor (k-value=0.02–0.00) kappa coefficients for males and females, respectively, highlight the direction specificity of functional asymmetry. These data show that whereas performance of the COD test improved, the magnitude of COD asymmetry declined across chronological age in youth tennis players.

This study examined changes in jump asymmetry in adolescents over a 72-hour period following a muscle fatigue-inducing protocol. Single-leg 10-s hop jump (SL10J), single-leg countermovement jump (SLCMJ), and single-leg horizontal jump (SLHJ) asymmetries were measured at baseline, immediately post-exercise, and at 24, 48, and 72 h post-exercise in 7 female and 16 male adolescents aged 12–18 years. The bioelectrical impedance analysis derived segmental phase angle and ECW/TBW were used as indicators of muscle damage for each leg, while the Visual Analog Scale (VAS) assessed muscle soreness and the bilateral countermovement jump (BCMJ) and the bilateral horizontal jump (BHJ) indicated changes in absolute jump performance. A significant increase in SL10J asymmetry was observed 48 hours post-exercise (p < 0.001), while no significant changes were detected immediately post-exercise or at 24 and 72 h. No significant changes were found in SLCMJ or SLHJ asymmetry at any time point. BIA did not indicate significant muscle damage, though a significant increase in muscle soreness (VAS), peaking at 48 h post-exercise, was recorded. The kappa values indicated slight to moderate agreement for task specificity and slight to substantial agreement for time specificity, with the highest consistency between 24 and 48 h post-exercise for both the SLCMJ and the SL10J. To conclude, asymmetry significantly increased only for the SL10J at 48 h post-exercise, suggesting that repeated jump tests may be more sensitive to fatigue-induced asymmetry than single-jump tests. The substantial kappa values at 24 and 48 h highlight the potential to offer a more robust assessment of asymmetry when recovering from a fatigue-inducing event.

Background: Inter-limb asymmetry is commonly regarded as a potential limitation for athletic performance and a contributor to injury risk. However, the influence of training status and sex on asymmetry in judokas remains poorly understood. Therefore, this study aimed to: (1) quantify inter-limb asymmetry in lean mass, bone mineral density, bone mineral content, and fat mass, and (2) examine how inter-limb morphological asymmetry varies across competitive levels (national vs. European) and sexes among young competitive judokas. Methods: Lean mass, bone mineral density, bone mineral content, and fat mass were assessed using Dual-energy X-ray Absorptiometry in 27 male and 21 female competitive judokas aged 13–17 years. Comparisons between limbs were performed using paired-samples t-tests. Differences in asymmetry across competitive levels (national vs. European) and sexes were analyzed using Mann-Whitney U tests. Results: Inter-limb asymmetry magnitudes ranged from 1.47% to 8.24% across groups. Overall, judokas showed greater values in the dominant limb compared to the non-dominant limb for most measures ( p ≤ 0. 010). Mann-Whitney U tests identified significant differences in asymmetry between competitive levels only in lower-limb fat mass for both males ( p = 0.015) and females ( p = 0.033), and in lower-limb bone mineral content for females ( p = 0.039). No significant differences in asymmetry were observed between sexes. Conclusion: While inter-limb differences were present, the magnitude of asymmetry was generally small (≤ 8%) and did not differ significantly between competitive levels or sexes. These findings suggest that reducing morphological asymmetry in judokas may not be a priority, regardless of competition level or sex.

Bio-electrical impedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA) are methods to estimate human body composition. This study aimed to compare sex-specific outcomes for estimating segmental and whole-body composition in 83 healthy participants (21.9 ± 1.5 years, 56% men) using Inbody S10 BIA and Norland Elite DXA devices. One-way repeated measures ANOVAs showed significantly lower whole-body fat% and whole-body fat mass values alongside higher whole-body lean mass values resulting from BIA when compared to DXA (both sexes: p < 0.001). In men, whole-body bone mineral content was significantly higher using BIA against DXA (p < 0.001). Regardless of sex, no significant BIA versus DXA difference was found in arm fat mass (men: p = 0.180, women: p = 0.233), whereas significantly lower leg fat mass values were found with BIA versus DXA (both sexes: p < 0.001). Additionally, significantly higher arm lean mass (both sexes: p < 0.001) and leg lean mass (only women: p < 0.001) were found in BIA versus DXA. Moderate to very strong positive associations (p < 0.05) between BIA and DXA outcome measures were found, except for arm fat mass (men: p = 0.904, women: p = 0.130) and leg fat mass (only men: p = 0.845). This study highlights (sex-dependent) differences in corresponding test outcomes between BIA and DXA both at the segmental and whole-body level.