Trunk rotation coordination in front crawl: which segment leads? Three coordination strategies and their dynamic changes across 400-m split progression in elite swimmers

Objective To identify upper-trunk–pelvic roll coordination strategies during 400-m front-crawl swimming and examine their kinematic characteristics, segment-wise distribution, and associations with swimming speed. Methods Twenty-two elite male swimmers completed a maximal 400-m front-crawl trial while two inertial measurement units recorded upper-trunk and pelvic roll. Cycle-level cross-correlation lag was used to classify coordination into upper-trunk-leading (UL), pelvic-leading (PL), and near-synchronous (NS) strategies. Kinematic differences among strategies and changes in strategy probability across 50-m segments and swimming speed were examined using Bayesian multilevel models. Results Across 2,796 valid roll cycles, NS was the most frequent strategy (53.04%), followed by PL (25.86%) and UL (21.10%). Strategy use varied substantially between swimmers. UL showed greater torso twist range than NS (NS–UL = −0.71, 95% CrI: −0.96 to −0.42) and greater torso twist velocity than both NS (NS–UL = −0.61, 95% CrI: −0.95 to −0.26) and PL (UL–PL = 0.62, 95% CrI: 0.19–1.04). In contrast, upper-trunk and pelvic roll ranges were larger in NS and PL than in UL, with no clear difference between NS and PL. Faster within-athlete speed increased the odds of UL relative to both NS (OR = 2.38, 95% CrI: 1.76–3.26) and PL (OR = 2.07, 95% CrI: 1.31–3.33). No clear segment effects or between-athlete mean speed effects were observed. Conclusion Elite 400-m front-crawl swimmers used three distinct upper-trunk–pelvic lead–lag strategies, with marked inter-individual variability. NS was most common, whereas UL was more likely at faster within-athlete speeds. These findings suggest that trunk coordination in elite swimmers is individualized rather than organized around a single optimal pattern.