Better in their words…

When Hoby Darling, the CEO of Skullcandy Inc., SKUL +1.40% was training for the Ironman 70.3 Hawaii, he thought he was the epitome of fitness. But after the 2009 race, which consisted of a 1.2-mile swim, a 56-mile bike ride, and a 13.1-mile run, Mr. Darling realized being fit for endurance races wasn’t the same as being fit overall.

The 38-year-old says his focus on endurance training—he has competed in more than a dozen marathons and many Olympic distance triathlons since the early 1990s—meant he was ignoring strength, balance and flexibility. “I began to think about how many pull-ups I could do: one or two,” says Mr. Darling.

When he returned from Hawaii, he typed “world’s hardest workout” into an Internet search engine. The film “300” popped up and Mr. Darling read in a news article how the film’s star, Gerard Butler, worked out “to get so huge for the film,” he says.

Mr. Darling, who was an executive at Volcom, a California skate, snow and surfboard apparel company at the time, searched for a similar workout and stumbled upon a CrossFit studio in Costa Mesa, Calif. CrossFit incorporates weight lifting, body-weight strength exercises and calisthenics done in rapid succession.

“What hooked me is that it was harder than anything I’d ever done,” he says. “I was sore for a week.”

Mr. Darling, who now lives in Park City, Utah, where the headphone and earbud maker is based, has since participated in CrossFit competitions and is certified as a CrossFit instructor. “I thought it would help improve my knowledge and form,” he says. “And I love helping other people achieve their fitness goals.”

The Workout

Four days a week Mr. Darling attends a 5:15 a.m. CrossFit session. Some days include sprints, push-ups, and burpees, other days might use kettlebells and medicine balls. “Every morning is something fun and different, but always a challenge,” he says.

On Thursdays, he participates in Skullcandy’s weekly team workout. When Mr. Darling joined the company in 2013, he started offering 6:30 a.m. boot-camp-style workouts at a space the company rents next to its offices. The sessions consist of push-ups, sit-ups, jumping exercises, plyometrics and sprints. Mr. Darling often leads the workouts himself or asks a co-worker with an athletic background to lead. “Our CFO is a former Army Ranger and we have a certified yoga instructor on staff,” he says.

Park City’s mountain location is a great base for outdoor activity. In the summer, Skullcandy has Tuesday-night bike rides and Friday-morning runs. Like many companies, it subsidizes gym memberships for employees. It subsidizes season passes to local ski resorts as well. “Any time there’s a powder day the team can get up on the mountain as long as they’re getting their work done,” he says.

On the weekends in the winter, he skis or snowshoes with his wife and his two daughters, ages 3 and 6. One day a week he does a long trail run.

The Diet

Mr. Darling tries to follow a Paleo Diet, which focuses on lean meats, vegetables, and nuts and excludes dairy and grains. “If I’m at a work dinner, I don’t get caught up in my diet,” he says. He says his weakness is ice cream.

Before his morning workout, Mr. Darling drinks a shake of whey powder, vegetable powder, chia-seeds, flax seeds, and liquid omega-3 fatty acids. “I’ve gotten used to the funny taste,” he says.

The sandwich shop across from his office knows his lunch order by heart: a chicken breast sandwich with vegetables and olive oil—hold the bread.

The Gear

As also a former executive at Nike, Mr. Darling says he gets much of his gear free or at a discount. He wears Nike Free Trainers and Nike Dri-Fit tights under Hurley Phantom board shorts for his CrossFit sessions. “The tights provide a lot of stretch for squats so I don’t have to worry splitting my pants,” he says.

He runs in Salomon Gore-Tex sneakers and wears Skullcandy Chops earbuds, which hook over the ear to stay in place. Mr. Darling says he has six or so mountain bikes in his garage. His favorite is a semi-custom Turner 5.Spot model. He says the bike was a splurge at $4,000.

The Playlist

“I’m a Spotify and Pandora junkie,” he says. His favorite stations are Eye of the Tiger, which plays songs similar to the ’80s hit, Maroon 5, Pearl Jam, Jimmy Buffett, and Rage Against the Machine.

Why Marathons Aren’t Enough: The Case for Mixing It Up

If you can run a marathon, you are fit, right? Not necessarily, says Richard Cotton, an exercise physiologist and the national director of certification for the American College of Sports Medicine in Indianapolis.

Exercise should include a variety of movements. “Doing the same activity every day, whether it’s typing at a computer or running, inevitably causes stress on your joints, which can lead to injury,” Dr. Cotton says.

He recommends trying a new activity at least once a month and for at least three workouts to see if you like it. “The easiest way to get variety is to try something new,” he says.

If you’re a runner, try adding swimming to your routine. “Having a workout that is 50% swimming and 50% running reduces the repetitive stress on certain muscles by 50%,” he says.

A regimen that is 50% aerobic, 40% strength and 10% flexibility is ideal, he says. “It doesn’t need to be intense,” he says. “Rather than a military-style push-up, simply push away from the kitchen counter at a 45-degree angle for a handful of reps each day.”

Runners or bikers could stop at a bench and do a triceps dip, where they grip the bench seat with their hands behind them. Then they walk their legs out to a 45-degree angle and lower themselves down and up. Or they could do pull-ups on a tree branch.

Exercise cards help guarantee a varied workout. List three exercises per muscle group on index cards and choose one from each, he says. And mix up the number of reps. “Just small tweaks make a big difference,” he says.

Write to Jen Murphy at workout@wsj.com