Beyond the Biological Clock: A Life-Course and Performance Analysis of Masters Swimming World Championships Participation

Age-related declines in sport participation and performance are commonly attributed to physiological constraints. This retrospective observational study compared the age patterns of participation and performance in masters swimming using 26,789 individual-event performances (expressed as the percentage change relative to each subgroup’s mean baseline race time at the youngest age) from three World Aquatics Masters Championships (2023–2025), in four strokes, sprint (50–100 m) and endurance (400–800 m) events, and both sexes. Participation, defined as individual-event performances (not unique swimmers) per million inhabitants of the corresponding age group, was modelled with polynomial and segmented regression; race-time deterioration (% above the 25–29-year baseline) with linear, quadratic and segmented regression compared by the corrected Akaike Information Criterion (AICc). Participation followed an inverted-U trajectory in all sex × distance groups, decreasing from 27 to approximately 37 years, rising to a peak in the early fifties (≈52 years) and declining thereafter. Race times deteriorated monotonically and non-linearly; quadratic and segmented models were statistically equivalent (|ΔAICc| < 2), with the rate of deterioration rising at approximate transition ages (not precise physiological thresholds) between the late fifties and the late sixties depending on the group. This divergence suggests that, up to the sixth decade, the age pattern of participation is not a simple reflection of the age pattern of performance. We propose, as a hypothesis, not tested here and to be examined with individual-level longitudinal data, that life-course and social factors may shape engagement in competitive masters swimming before physiological constraints become predominant.