Age-Related Breakpoints in Pacing Variability and Performance in Masters Swimmers: A Segmented Regression Analysis of World Championship Male and Female Data

<b>Background:</b> Pacing critically influences swimming performance. In master swimmers, aging leads to performance decline, but the age at which pacing becomes unstable, and whether this precedes performance loss, remains unclear. <b>Objective:</b> This cross-sectional retrospective study analyzed sex, distance and stroke-specific age-related breakpoints in pacing variability (CV) and performance (RT) in master swimmers. <b>Methods:</b> A total of 13,822 swimmers (7417 men and 6405 women; age 25-99 years) competing at the World Aquatics Masters Championships (2023-2025) were included. <b>Results:</b> CV showed the strongest association with RT (r = 0.173, <i>p</i> < 0.001). Overall, CV worsened significantly earlier (52 years, +2.82%/year) than RT (82 years, +0.51%/year; <i>p</i> < 0.001). In women, CV deterioration began at ~50 years, while RT was maintained until ~85 years; this was particularly pronounced in short-distance events (pacing breakpoint at 35 years). Men displayed more synchronized decline patterns. Age breakpoints of CV and RT were coincident in freestyle and breaststroke (82 years). Backstroke and butterfly demonstrated RT breakpoints at 47 and 67 years, respectively, with CV occurring at 72 years. <b>Conclusions:</b> These findings indicate that CV generally deteriorates years before RT and represents a stroke, sex and distance-specific marker of accelerated functional decline in elite master swimmers. Monitoring CV may provide early warning of impending performance deterioration informing timely, targeted training interventions to extend athletic longevity.