The modern evolution of long distance running and swimming is documented statistically: body mass (M), height (H), slenderness (S), and winning speed (V). In long distance running (10,000 m), M, H, and S are decreasing: these trends contradict the trends in short distance running (100 m). In long distance swimming (1,500 m freestyle), the trends are similar to short distance (100 m freestyle): H and V are increasing. The parallel trends in long versus short distance swimming, and conflicting trends in long versus short distance running are due to dehydration, which is limiting only in long distance running. The speed records ratio running/swimming for long distance sports is decreasing at the same rate as for short distance sports. Running and swimming are subject to speed ‘ceilings’ (Vmax) dictated by physics: the current record speeds in running and swimming are close to 1/2 V max.
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