Washington, July 18 - Swimmers keep getting bigger, with the shortest one in any race towering over the average spectator, as former Olympian Rowdy Gaines pointed out during the 2008 Beijing Games.

What may have been seen as an off-hand remark turns out to illustrate a trend in human development -- elite athletes are getting bigger and bigger.

What Gaines did not know was that a new theory by Duke University engineers has indeed showed that not only have Olympic swimmers and sprinters gotten bigger and faster over the past 100 years, but they have grown at a much faster rate than the normal population.

Furthermore, the researchers said, this pattern of growth can be predicted by the constructal theory, a Duke-inspired theory of design in nature that explains such diverse phenomena as river basin formation and the capillary structure of tree branches and roots.

In a new analysis, Jordan Charles, an engineering student who graduated this spring, collected the heights and weights of the fastest swimmers (100 metres) and sprinters (100 metres) for world record winners since 1900.

He then correlated the size growth of these athletes with their winning times.

'The trends revealed by our analysis suggest that speed records will continue to be dominated by heavier and taller athletes,' said Charles, who worked with study co-author Adrian Bejan, engineering professor who came up with the constructal theory 13 years ago.