EVERETT, Mass. — Brian McNamee, the onetime personal trainer for Roger Clemens, resurfaced to give a brief motivational speech to a small group of workout buffs on Thursday.

In his first public comments since testifying that he injected Clemens with steroids and human growth hormone, McNamee gave about 25 high school athletes, coaches and parents a warning about mistakes that can tarnish one's reputation.

"My lifetime of actions can be defined by one singular monumental mistake," he said in a 12-minute talk at a friend's supplement store. "I'm trying to learn from my mistake. I want you to learn from my mistake and other peoples' mistakes."