Tyson Gay never realized how harmful stress could be until the American sprinter returned from a doping ban last year.

"It was so stressful, my hair started thinning," Gay told Reuters as he prepared for this week's US world championships trials in Eugene, Oregon.

The hair is fine now, maybe even a little longer than when Gay became a double world sprint champion in 2007 and set the US 100 meters record two years later.