North America's top fitness professionals don't necessarily train celebrities and professional athletes or badger overweight reality-TV contestants into shape.
Instead, they work with recreational runners who want to get faster, they inspire virtual clients online and they make fitness classes innovative and challenging.
These three fitness phenoms were all recently honoured by their industry as the cream of the crop. They've shared a few of their most effective secrets to help you get motivated or refresh your workouts:
Karp aspires to be "the Jillian Michaels of running," if only because the broad exposure would help him reach runners of all abilities. Karp is a big fan of the objectivity and the science of the sport:
In races, there's a start line, a finish line and one winner.
“I've always been interested in what makes someone faster than another person and how they got there," said Karp, the 2011 IDEA Health and Fitness Industry Personal Trainer of the Year who works in San Diego.
“People think running is so simple," he added. "But a lot of people giving running advice have no idea what they're talking about.”
Karp's top tips:
Polarize your training. Recovery is the secret behind improvement; it can mean taking a day off or working at a lower intensity.
With runners, Karp stresses going all out on hard days and relaxing on easy days. "Most people — especially gymgoers — make their workouts all in the middle," he said.
“It's the same thing every day. With really hard days, you force adaptations that cause stress; then you recover by working easy."
Ease into it. If you've been sedentary for 40 years, don't sign up to run a marathon in six months.
The other thing that drives Karp crazy? Going out too fast during the first mile of a race. Run a pace you can maintain the entire time, Karp said.
Make interval workouts harder. Many runners try to do this by running the intervals at a faster pace. Instead, decrease your recovery time between intervals, make the interval period longer or increase repetitions.
“Raise the peak of the pyramid from the bottom," Karp said. "You'll be producing more mitochondria to do the aerobic work. When you can do more and more work at the same intensity, you'll be getting faster."
The 29-year-old Nichols, recognized as "America's Top Personal Trainer to Watch" by the American Council on Exercise and Life Fitness, has been on both sides of the fitness fence.
As a teenager, she developed unhealthy exercise and eating habits — even though she thought she was working out correctly. In college, she struggled, bouncing from intense workouts to bagging exercise and gaining 40 pounds.
"I was miserable," Nichols, of the Cincinnati area, recalled.
“But as she learned more about personal training, she discovered "how to practice moderation, not just in food, but exercise," she said.
“Fitness isn't about achieving a certain physique or going to extremes. It's about exercising in ways that are fun, fit into life easily and don't cause you to give up other things.”
Nichols' top tips:
Morning exercise works. Get up 15 minutes earlier to squeeze in a short workout. "It's one of the best ways to make sure nothing gets in the way," she said.
As a non-morning person, Nichols forces herself up and out of bed two to three days a week for a run, knowing that she'll feel far worse if she blows it off. Make it easier: Sleep in your workout clothes.
Don't work out on an empty stomach. "It's not going to result in greater fat burning," said Nichols.
“What's most important for weight loss is burning total calories. If you are not eating in the morning or for a long time before you exercise, you won't be able to work out at an optimal level, and that's more detrimental," she said.
About 30 minutes before a workout, try a small snack of 100 to 200 calories, which could include fruit juice, half a bagel or an energy bar with three to five grams of protein and at least 15 grams of carbs.
If you have an hour or two, try whole grain crackers with nut butter, hard-boiled eggs, nuts or oatmeal.
Walk — even if you can run. Walking is an important part of an exercise plan, even for fit people.
“Every bit of physical activity is beneficial," Nichols said. "It's wrong for people to think they have to work out intensely to benefit. In fact if your workouts are always intense, you might be setting yourself up for failure.
“If you're having trouble getting started, just do 10 minutes a day to start building a habit. "That's over an hour a week. Then work up to three 10-minute chunks in a day," she said.
Crews, IDEA's Fitness Instructor of the Year, has what her husband jokingly calls a "certification addiction."
Over the last three decades, the 55-year-old dynamo from Alabama has taught everything from step aerobics and glide classes to her current favourites: TRX Suspension Training and Batuka, a new pre-choreographed dance fitness programme.
The challenge for fitness instructors is that "we need to have the depth of a personal trainer and, at the same time, we have to distill our instructions down to their very essence to serve a group situation," she said. Her passion now is training other fitness professionals, which she does through her fitness education company, Dynalife.
Crews' top tips:
Find what you like.
Then do it. “Make that the cornerstone of your workout, because if you don't like it, you won't stick to it," she said.
Round out that activity with something complementary. If you like to run, for example, then run. But balance it with some yoga or strength training.
Eat food as close to its natural state as possible. Eating the orange is always better for you than drinking the orange juice.
Also stay away from refined or processed foods and limit the amount of high-fat protein such as meat that you eat each week. "Going all veggie is always an option," Crews said.
Don't hang out in the back row. Group fitness classes can improve your odds for success, as the class tends to become one big family, said Crews.
But if you're uncertain about your abilities, "let the instructor know you are a newbie, and position yourself where you can see yourself in the mirror and see the instructor," said Crews.
“It will be much easier to follow, learn and look like you already know what you're doing in there.”