There was a time in boxing's history when no one packed a punch inside or outside the ring like the latest, greatest American heavyweight. As the class of Muhammad Ali, George Foreman and Mike Tyson went, so did boxing.

It seems long ago. The sport belongs these days to two welterweights, Floyd Mayweather Jr. and Manny Pacquiao, who won't fight each other. The top heavyweights, Wladimir and Vitali Klitschko, are Ukrainian brothers who box mostly in Germany and also won't fight each other.

And now some sweet scientists believe the prospect with the best shot to rise in the ranks of American heavyweights isn't even a full-time boxer.

Bryant Jennings, 27, has been employed for the last six years as a mechanic in the Federal Reserve Bank of Philadelphia's facilities department. He works from 7:30 a.m. till 4 p.m. Sometimes he runs seven miles from his home to the bank, where his duties include carpentry, plumbing and electrical repair. "We fix just about everything," he said.

When he finishes laboring at his day job, Jennings moonlights as an undefeated heavyweight. He just wrapped up training for his fight Saturday against Steve Collins at the Prudential Center in Newark, N.J.