BACKGROUND: Sprint butterfly performance depends on the interaction between propulsive force production and hydrodynamic resistance. Load-velocity profiling has been used to characterize mechanical capabilities in swimmers, yet it remains unclear whether load-velocity parameters differ across objectively defined performance levels and whether they demonstrate graded associations with sprint performance. The aim of this study was to examine differences in load-velocity variables between three objectively defined performance levels in male 50 m butterfly swimmers and to determine their association with sprint performance expressed as World Aquatics (WA) points. METHODS: Thirty-nine male swimmers were classified into three performance levels (n = 13 per level) based on their highest WA points in the 50 m butterfly. Semi-tethered maximal butterfly sprints were performed under three external loads using a robotic resistance device. Theoretical maximal velocity, theoretical maximal load, load normalized to body mass, and slope of the load-velocity relationship were derived from individual linear regressions. One-way analysis of variance, Pearson correlations, and analysis of covariance controlling for body mass were conducted. RESULTS: Significant differences were observed between performance levels for all load-velocity variables (p * 0.003). Theoretical maximal velocity showed the largest effect size (partial eta squared = 0.75) and was strongly correlated with WA points (r = 0.91, p < 0.001). Differences remained significant after adjusting for body mass. CONCLUSIONS: Load-velocity profiles differ across performance levels in male 50 m butterfly swimmers and demonstrate strong graded associations with sprint performance. Theoretical maximal velocity may represent a key mechanical characteristic underlying competitive standard.
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