The history of the race to determine who is the world's fastest human tells us that maximum interest is generated whenever someone rises to challenge the top dog.

That makes Tyson Gay wonder why he can't be the one to rise as the next primary challenger to Asafa Powell, the acknowledged leader in the 100 meters since setting the world record of 9.77 seconds in June 2005 and matching the time twice after that.

"I hope so," Gay said yesterday at Franklin Field as he prepared to compete in today's USA vs. the World competition in the Penn Relays. "I'm really working hard, and I'm sure Asafa wants more competition. I want this to be a rivalry. I want to step up to the plate."

It would have been nice if this competition could commence today with Gay's running on the U.S. 4x100-meter relay team and Powell's representing Jamaica. But Powell, through a spokesman, pulled out of the race earlier this week.

And Gay, although he said he has a lot of respect for Powell, appeared a bit miffed at the world-record holder's absence from the carnival.

"I was looking forward to seeing him run at Penn," Gay said. "I was just a little upset that he didn't show up. I ran at [Mount San Antonio College in California], but he didn't get to run. We haven't gotten to run a relay to see how the outcome is going to be.

"I look forward to running against him. He's a great competitor. I don't know if I'd say he's a friend, but we speak, and we joke around. I really respect him as an athlete and as a person. He carries himself in a very humble way. I just know the fans were looking forward to seeing him."

Gay, 24, of Lexington, Ky., significantly bettered his personal-best times in the 100 and 200 during the 2006 season. His 19.68-second time in the 200 was the fastest in the world, and his 9.84 in the 100 was second-fastest to Powell's pair of 9.77s.

Gay credited a deliberate training program developed by his coach, Lance Brauman, with helping him to improve and compete injury-free. He said he needed to improve his start and his strength to continue on an upward path.

"I'm working on my start, and I hope to improve it," he said. "My strength level isn't up yet, and my positioning isn't right. I need to work on that."

Gay first ran at the Penn Relays as a collegian at Arkansas. Last year, he led off the victorious U.S. team that won the 4x100 in 38.33, with Olympic gold-medalists Shawn Crawford and Justin Gatlin running the final two legs.

But while Crawford is expected to run today, Gatlin is nowhere to be seen. He received an eight-year ban last July for testing positive in a doping test. Gay now has a chance to be a leader of the young group of sprinters coming up, one that includes Wallace Spearmon, his former Arkansas teammate.

"I've been running professional track as long as Wallace, but he's younger than me," Gay said of his 22-year-old teammate. "I'm hoping to bring some maturity and some unity to the team so everyone comes together."

The USA vs. the World relays today will feature 4x100 and 4x400 relays for men and women, a distance medley for men, and a sprint medley for women.