Inter-Limb Hand Force Asymmetry in Front Crawl Swimming: Individual Interpretation Using BAI-1, MDD, and MID

This study examined inter-limb hand force asymmetry in competitive swimmers during front crawl at two paces (200 m and 50 m). Eight national-level swimmers (18.3 ± 2.5 years) performed 25 m trials at both intensities using wearable force-sensing paddles. Asymmetry was assessed with a traditional percentage-based index (BAI-1) and distribution-based estimates, namely the Minimal Detectable Difference (MDD) and an exploratory Minimal Important Difference (MID) estimate. Mean hand force was significantly higher at sprint pace (50 m) compared to 200 m pace (p < 0.001), confirming adherence to the prescribed intensities. Using BAI-1, swimmers showed a wide range of asymmetry values (<2% to >10%), highlighting substantial inter-individual variability. Absolute BAI-1 was descriptively higher during the 50 m pace than during the 200 m pace, although this difference was not statistically significant. Distribution-based estimates refined the interpretation: MDD corresponded to 4.48% and 4.83% for the 50 m and 200 m paces, respectively, whereas the exploratory MID estimate corresponded to 2.68% and 2.89%. These findings illustrate how BAI-1, MDD, and MID may lead to complementary interpretations of asymmetry. The combined use of traditional indices and distribution-based estimates may support more individualized monitoring of inter-limb hand force asymmetry in swimming and potentially other bilateral sports.