Elite swimmers do not exhibit a body mass index trade-off across a wide range of event distances

Abstract

There is a trade-off reflected in the contrasting phenotypes of elite long-distance runners, who are typically leaner, and elite sprinters, who are usually more heavily muscled. It is unclear, however, whether and how swimmers' bodies vary across event distances from the 50 m swim, which is about a 20-30 s event, to the 10 000 m marathon swim, which is about a 2 h event. We examined data from the 2012 Olympics to test whether swimmers' phenotypes differed across event distances. We show that across all swimming event distances, from the 50 m sprint to the 10 000 m marathon, swimmers converge on a single optimal body mass index (BMI) in men's and women's events, in marked contrast with the strong inverse relationship between BMI and event distance found in runners. The absence of a speed-endurance trade-off in the body proportions of swimmers indicates a fundamental difference in design pressures and performance capability in terrestrial versus aquatic environments.

Keywords: evolution; locomotion; running; sports; swimming; trade-off.

Figure 1.

Relationship between race distance and BMI in runners and swimmers in men's and women's events. Full model results in table 1. The boxplot centre line is the median. The lower and upper margins of the box are the first and third quartiles, respectively. The upper whisker is the third quartile plus 1.5 times the interquartile range. The lower whisker is the first quartile minus 1.5 times the interquartile range. Outliers appear as points.

Figure 2.

Interaction plot for four sets of events matched by duration. Mean BMI, mass and height are given for each set. S, swimmers; R, runners.