In "Slow and Steady Loses the Race" in today's WSJ (subscription required for access to entire article), Cameron Stracher addresses a question of interest to me (see July 2007 post): Why have times for U.S. middle and long distance runners risen, not just relative to their current rivals but relative to American runners of the 1970s?
Stracher draws from research on a book project on the running boom of the 1970s. He notes
Except for Ryan Hall (on a faster course in London), no American-born runner has ever run faster than Alberto Salazar's 2:08:13 marathon in New York in 1981. Meanwhile, three times as many male runners achieved the same qualifying time in the U.S. Olympic marathon trials in 1984 as in 2008. The story is the same at nearly every event up the distance ladder. With the exception of a few standouts (for example, Alan Webb), U.S. runners cannot match the times of their earlier progenitors
The flattening or worsening of times by elite runners coincides with a drop in times at the mean or median. The decline by the masses reflects an increase in participation -- drawing runners from farther down the distribution of abilities. Answering the question for elite runners is not so easy. Stracher makes out increase at participation through marketing ("just do it") and softening (shortening races, focus on participation) as not just coincidental to but causal for the decline at elite levels.
Maybe, but I'm not sold. As he notes, you don't see greater participation leading to fewer sub-par rounds in golf. What's happening at the extreme "right tail" of the ability distribution may owe to its own set of influence. The most prominent may be a wealth/effort effect. Boxing is the template. Where have the great American born boxers gone? The rising tide of living standards along with the rigors and dangers of the sport have driven them to other pursuits. Running isn't dangerous but certainly demands tons of effort and pain. Even at the 400m level where American born athletes have performed well, few have stuck with it for the long haul. Other than Michael Johnson, not many wanted to endure year after year of oxygen debt-laden repeats. Quincy Watts, although very gifted and successful, came and went in a hurry.
[ I should note that American born women, after a couple of decades of virtual non-existence at the international level, are enjoying a resurgence in performances in recent years led by Deena Kastor (bronze 04 Olympic marathon), Shalane Flanagan (bronze o8 10,000m), and Kara Goucher (bronze 07 10,000m).]