Contrary to the outdated locker-room myth, the reason you hit your limits is not simply that lactic acid is scorching your muscles. Instead, the sensations you feel while running each correspond to a different minicrisis in your body, and they combine to determine whether you can hold your pace.
Last spring, scientists from around the world gathered in San Diego for a special conference to share the latest results in their search for the ultimate limits of endurance. They discussed hot new topics like metabolites and mental fatigue, as well as the familiar foes like heat and hydration. Here is what their findings reveal about what’s behind the pain of pushing for a PR.