As for their personal relationship, it appears to be cordial enough even though they have contrasting characters and backgrounds. While Liu seems relaxed and may find time to wink at the camera when preparing for a race, Trammell will typically hide behind his shades and go through his warm-up routine with a studied concentration.
"We don't communicate too much beside saying `hello' because of the language barrier," Trammell said. Like true sportsmen, however, they usually find time to congratulate each other after a race with a hug.
Both men see themselves as inheritors to the crown of US Olympic gold-medal hurdler Allen Johnson, who dominated the sport from 1996.
Trammell used to train with him until 2002, while Liu was a self-confessed fan of Johnson and even asked for his autograph at the 2002 Grand Prix in Lausanne.
But while Liu has arguably eclipsed his hero, Trammel is in danger of living in his shadow. When Johnson finished ahead of Trammell at the 2003 World Championships, Trammell beat Liu and looked set to carry the torch in the traditionally American-dominated sport.
Instead, Liu found another gear, won the 2004 Olympics and hasn't looked back since. If he did, he would see Trammell on his heels.
Asked whether this was a source of disappointment, Trammell reasoned he has achieved a great deal and the best is yet to come.
"I feel blessed to have those silver medals because to make the team in the US is tough enough, let alone make the podium at the Olympics. I feel that when it's my time to win gold I will Aug. 21, 2008."
"The secret to my success is my faith and determination. I feel that these things are the foundation to being successful in anything."
Liu may have one-fifth of the global population behind him, but when the big day arrives, Trammell will be looking for that split-second lapse in concentration to cause the biggest upset of the Beijing Games.
