Every Friday morning at dawn, a cadre of hedge-fund executives, investment bankers, and securities traders meet in New York City's Central Park and proceed to push one another to the physical limit – honing their edge before their competitors even wake up. The park's natural landscape becomes a gauntlet. They hoist 40-pound sandbags and sprint up hills, bear-crawling down steep steps and alternating burpees with box jumps on park benches.

After that hour of pain, "I can crush it all day," says Rob Vespa, the 40-year-old head sales exec at Bradesco Securities. "I'm on the desk by 7 am, people are just filtering in, and I'm already eating my second breakfast, feeling great, mentally strong," he says.

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The group's official name is the Bfast Club – for breakfast and for speed. It started in 2011 with two fitness-obsessed hedge funders. Now they're joined by friends from other firms and out-of-towners in the city on business. Many are former college athletes, military vets, or serious triathletes and marathoners. Tommy Seier, a 34-year-old executive at Signpost Capital, has completed more than 55 triathlons, including five Ironman races.

The same competitive spirit that drives Wall Street is always present. Peer pressure keeps everybody honest. (It's better to haul your hungover carcass to the park than sleep in and face the goading emails later.) One recent Friday, a hedge-fund executive named Pierce Archer – at 44, one of the group's oldest – outlasted the rest in the final core workout, keeping his legs in boat position for more than two minutes, as younger men collapsed trembling. Says Archer: "I have a saying I repeat in my head: 'Remember the guy who gave up? Neither does anyone else.' "