The 39-year-old American, who weight 474 pounds at the start of filming, quipped: "I never worked this hard when I was trying to make the Olympic team!"

Gardner's partner in the two-member team, Justin Pope, weighed in at 365 pounds and lost 27 pounds.

With each dropping seven per cent of his body weight, Gardner and Pope combined to lose 59 pounds - tops among the 11 teams in the competition.

They also won the first challenge, which was for each team to run five kilometres (3.1 miles) on a treadmill.

Taking turns, Gardner and Pope were the first to complete the run.

That earned them the right to get the first turn at a surprise choice.

The option was whether to do their subsequent training under the familiar training stars of the show, slim, trim Bob Harper and Jillian Michaels, or go with two, new "mystery" trainers.

If they selected the unknowns, Gardner and Pope were offered four weeks of immunity from being eliminated from the show.

They chose the unknowns - who were not revealed - and the immunity.

Gardner weighed in for the 286-pound class when he won Olympic gold in 2000.

When he won bronze at the 2004 Olympics, he competed in a weight class that had been cut down to 264.5 pounds.

At the Biggest Loser weigh-in, the combined weight of Gardner and Pope was 839 pounds, highest for any of the teams at the California ranch where the show is taped.

Interviewed on the show, Gardner had tears in his eyes as he discussed his weight gain, and other contestants cried too.

"It's a shame. It's a tragedy. It's horrifying for me and my family," said Gardner.

"I want to become the person I was."

The show will continue through to a live final in May.