Alton Marsh lost more than 40 pounds in 2013. (Teddy Wolff/For Express) Alton Marsh lost more than 40 pounds in 2013. (Teddy Wolff/For Express)

When it comes to weight loss, the stakes for Alton Marsh are sky-high.

The 69-year-old aviation writer has been assigned a piece that requires flying in a P-51, a teeny-tiny plane from World War II that was designed to carry just a pilot. With modifications, a passenger can come along. But that person can’t look like Marsh did at the beginning of 2013 — at 6-foot-1 and 239 pounds, he wasn’t about to squeeze into anything.

Marsh admits he hasn’t been disciplined about watching his weight, which nudged upward over the years. Even when he got on a jogging kick a while back, there was no guarantee he’d actually log mileage.

“I’ve put on running clothes and gone to the park, and then I’ve driven to Panera Bread instead,” Marsh says.

Last March, determined to get in flying form, Marsh joined Sport & Health’s North Frederick, Md., club, near his home, and signed up with personal trainer Jenny Foit. The plan she devised for their twice-a-week appointments was tougher than anything he’d ever done alone.

“I call them beat-up sessions,” says Marsh, who found himself on an inclined treadmill dashing faster than he thought possible. (“She’d say, ‘Can you do eight?’ And I’d say, ‘Of course not,’ ” he says. But he did intervals at 8 mph.) Then came situps, pushups, assisted pullups, moves on exercise balls and so on.

When Marsh had knee surgery shortly after they started training together, Foit switched to mostly upper-body exercises.

The weight kept coming off, which Marsh attributes to Foit’s nutrition advice. The hardest food to give up? The mint ice cream sandwiches that had become part of Marsh’s daily diet.

“I had to forget them now and forever,” Marsh says.

Marsh shows off his TRX skills at a class led by personal trainer Jenny Foit. (Teddy Wolff/For Express) Marsh shows off his TRX skills at a class led by personal trainer Jenny Foit. (Teddy Wolff/For Express)

That didn’t change when he reached his goal of getting under 200 pounds this fall. He knew he’d need to maintain through the holidays in order to get on that plane in January. And Marsh recently got word that his flight has been pushed back until April, so he has to keep it up even longer.

His strategy is to change things up while still pushing himself. He’s switched from personal training to TRX group training with Foit, so she can monitor his progress.

“Al has followed me through everything. If I had a class called jumping off a bridge, he’d do it,” Foit says. He’s her assistant in the sessions, gathering mats for the other students before class and demonstrating plank variations with his impeccable form.

Marsh may be the oldest person in the room, but that doesn’t stop him from holding the positions longer and pounding out more reps than anyone else.

“One of my goals was to humiliate others,” jokes Marsh, who can list other perks that have accompanied his 40-pound (and counting) weight loss.

Tests from a recent doctor’s appointment show that his cholesterol levels have plummeted, which means he no longer needs medications he’d been taking for a decade. He’d developed a waddle to counterbalance his extra weight, but he can walk normally again. And he’s shopping for slim-fit pants.

He’s ready to turn 70 in February (“I’m up there, and my weight is down there,” he says), and then finally take that long-awaited plane ride. He’s nervous, however, about what will happen once he lands.

“After April, it’s uncharted territory,” Marsh says. But he has an idea for how to keep his resolution going in 2014: Zumba.