Has (natural) athletic performance peaked?

In the sports that best measure athleticism — track and field, mostly — athletic performance has peaked. The studies show the steady progress of athletic achievement through the first half of the 20th century, and into the latter half, and always the world-record times fall. Then, suddenly, achievement flatlines. These days, athletes’ best sprints, best jumps, best throws — many of them happened years ago, sometimes a generation ago.