EUGENE, Ore. — At the 2012 London Olympics, Aries Merritt of the United States won a gold medal in the 110-meter hurdles. Several weeks later, he shattered the world record in 12.80 seconds, his braids gathered in a ponytail, his left leg jabbing over each hurdle like a celebratory finger.
A year later, Merritt faded to sixth at the 2013 world track and field championships in Moscow. He had none of his usual acceleration over the final five of 10 hurdles. This was his strength, late speed, little deceleration. Something was wrong.