Five years ago, Sgt. Demond Johnson was told he could choose either Michigan or California as the next stop in his army career. Sunny San Diego beckoned, but after Johnson finished catching his breath at the cost of homes there, he decided to build his own outside Ypsilanti. As it happens, though, he flies fairly often to southern California these days, not for the army, but for his second career as a fitness coach. He’s thrice appeared with clients on NBC’s popular weight-loss reality show The Biggest Loser.

Being on TV didn’t faze him–but then he’d already experienced the ultimate reality show: combat in Iraq and Afghanistan. “It gives you perspective,” says Johnson, thirty-six.

Johnson’s studio, A2 Professionals, is a monochrome room on Eisenhower lined with mats and shiny exercise equipment. He stands six feet three and weighs a trim 193 pounds; his black T-shirt commands, “Shut Up and Sweat.”

In the army, Johnson is responsible for the physical fitness of reservists on seven Michigan bases, from Livonia to Bay City. In person, he’s so polite that it’s hard to imagine him saying “Shut up” to anyone, even out-of-shape part-time soldiers. When putting reservists through push-ups and drills, he says, he tries “to be calm but stern.”

He shows a softer side working with client Kyra Clark, twenty. “Good job!” he exclaims, as she pedals an exercise bike. “Now give me everything you’ve got. Sweat!”

Clark, five feet four, weighs about 485 pounds; she’s obviously struggling, but gamely pedals on. A student at Wayne County Community College, she met Johnson through another of his clients, and he agreed to take her on without charge. “He’s like a father figure,” says Clark, who as a kid gained a lot of weight after steroid treatments for asthma. “He’s a big part of my life right now.”

Johnson’s own complicated life currently includes housing and working out with twenty-five-year-old Mike McGinn, a contestant on The Biggest Loser, who at intervals has been flying to California with Johnson for filming. The footage will air on the show’s twelfth season starting in September. McGinn’s wife is also living at the house, along with Johnson’s family–his wife, Berkis, who works at the studio as a personal trainer, and their fifteen-year-old son, Ahmad, who was initially excited about the Biggest Loser connection but is now a bit bored by the whole thing.

Johnson found his new career by chance: about four years ago, an Ann Arbor Rec and Ed staffer saw him working out at a gym and asked him to teach a fitness class. Soon he was doing everything from teaching a “Warrior Challenge” at the Washtenaw Rec Center to running conditioning programs for Pioneer High softball and football players.

Eventually he met up with father and daughter Darrell and Andrea Hough, becoming the Ann Arborites’ head coach last year when they competed as a team on The Biggest Loser. Between them, the Houghs lost 268 pounds. Both now coach part time for Johnson’s studio and give motivational speeches.

The Biggest Loser gets flack from critics who charge that it exploits the raw emotions of competing teams of morbidly obese people, and Johnson acknowledges the show plays up the rivalries and the occasional emotional outbursts. “I don’t agree with it 110 percent,” he admits, adding he’s even heard complaints that he’s “too calm” during filming. He also acknowledges “some jealousy” on the part of a few local trainers about his TV exposure. His answer, in essence, is that there’s business enough for everyone. He’s currently working with seventeen clients, ranging from a couple of young teens whose parents think they need more exercise to an eighty-two-year-old man.

Johnson plans to retire from the army next year to work full time on his fitness career. He says matter-of-factly that his identity as a soldier extends to fighting America’s “war on obesity.” He is particularly concerned about children who spend all day indoors, glued to phones and computer screens. Though he knows there are kids in his neighborhood, “I don’t see them riding bikes any more,” and none has ever knocked on his door seeking a job mowing the lawn or shoveling snow.

Johnson’s fitness soldiering includes volunteering with walkers in a summer Saturday program sponsored by the Packard Health clinics. Earlier he helped launch a U-M program, “Men on the Move.” He says the essence of any weight loss program is discipline: the refusal to eat that longed-for chocolate cupcake, the willingness to grind away on that boring treadmill.

Raised in New Orleans, Johnson got a head start in the discipline department: his father was a career military officer who regularly inspected the rooms of Demond and his older brother and insisted that they complete their household chores before they could play. “We joke that our upbringing was like being in boot camp,” says Johnson.

A state high school wrestling star, he joined the army right after graduation, later earning an education/political science degree at Methodist College (now Methodist University) in Fayetteville, North Carolina. He went to school evenings while training soldiers at Fort Bragg during the day.

From 2001 to 2005, he spent much of his time serving overseas, narrowly escaping with his life when an explosion just missed his tank in Iraq. “It was a huge adrenaline rush,” he says, with characteristic understatement. Johnson credits counseling and exercise with helping him to deal with the post-traumatic stress of combat. Long bike rides, he says, help keep painful memories at bay.

He exudes the satisfaction of someone who has found his calling. And thanks to his Biggest Loser connection, he’s gotten off to a quick start in his second career. Last year, he was invited to Texas to work with a high school fitness program. While he was there, he also worked with former contestant David Griffin (“Season Four. I was ‘Cowboy'”). “It was a great experience for me to learn from Demond and sharpen my toolbox, so to speak,” says Griffin, who is also now a personal trainer. Johnson, he says, “was able to teach me how to tap into your client’s ‘inner warrior.'” Besides, Griffin says with awe, “He can do more ‘one-up’ push-ups than anyone I’ve ever known.”