For years, David Sharrow ran at least an hour three days a week without losing weight or gaining muscle. “I was basically getting nowhere,” he recalls. Now, Sharrow’s cardio routine doesn’t exceed 45 minutes a few times a week, yet he’s lost more than 25 pounds, reduced his body fat by close to 14 percent, and his running pace has still improved by a few miles per hour. He eats more these days, too. “It’s been exactly what I’ve been looking for,” says Sharrow, a 48-year-old attorney in New York City.

What changed? Sharrow underwent metabolic assessments at his gym, which revealed how and when his body burns fat versus carbohydrates. Through work with a personal trainer and other fitness and nutrition professionals, he altered his exercise routine to include more strength training and revamped his diet to include less bread and more protein and fat.

“Figuring out how to adjust my nutrition and my workouts really flipped a switch,” says Sharrow, whose 10- to 16-hour workdays make efficient workouts a priority. “People I haven’t seen in a while remark that they miss my twin brother, who was substantially rounder.” His primary care physician has applauded his drop in blood pressure and improved body composition, too.

[See: How to Lose Fat Fast — and Fit Into Your Skinny Jeans.]

Sharrow’s “twin” is an example of what some call a “non-responder” to his exercise routine, or someone who’s working out but not achieving the results he or she wants or expects, be it a trimmer waistline, bigger muscles, a faster mile or better endurance.

“It’s become an important term based on research showing that people don’t see the benefits of exercise that they’ve been told to [anticipate,]” says Neil Johannsen an exercise physiologist and assistant professor in Louisiana State University’s School of Kinesiology, which is a member of the American Kinesiology Association. In one study, for example, he found that only about 60 percent of people with Type 2 diabetes improved their VO2 max — a measure of cardiorespiratory fitness — after nine months of training. The big question in the field, Johannsen says, is: “How do we get everyone to respond?”

And while any type of exercise is likely beneficial in some ways for everyone, if you can’t understand why you’re not seeing the results you want, experts suggest these tips:

1. Track your progress.

You can’t be sure you’re not making progress unless you have a way to monitor it. While Sharrow went about it in a high-tech way (such assessments can take more than an hour, cost hundreds of dollars and involve exhausting yourself on a treadmill or other piece of cardiovascular equipment while wearing a mask that tracks your carbon dioxide output), simply using a pen and paper to track and increase your repetitions or mileage, for example, is better than nothing, says Steve Milkovich, the Minneapolis-based assistant program manager of assessments and health technologies for Life Time, the health chain to which Sharrow belongs.

“Exercise is all about adding adequate stress: The more times you do something, the less stress it’s putting on the body,” Milkovich says. It’s kind of like going to the same well over and over again; eventually it’s going to run out.”

2. Manage expectations.

If you’re not meeting your goals, you might first assess if your goals are even achievable, says Brynn Putnam, founder of Refine Method, a high-intensity interval training studio in New York City. “The way your body looked at 18 or 20 may not be the most relevant information to how your body looks at 40,” she says. Similarly, she says, expecting to get the same outcomes as a friend in the same program isn’t always possible and is rarely helpful.

Johannsen, who’s also the scientific director for exercise testing and intervention at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, suggests starting with the U.S. Department of Health and Human Services’ recommendations for physical activity: 150 minutes a week of moderate-intensity exercise (walking counts) or 75 minutes a week of “vigorous” exercise, which doesn’t necessarily mean beating yourself up at a high-intensity boot camp.

[See: Easy Ways to Get 10,000 Steps a Day.]

“Healthy doesn’t mean you’re 10 percent body fat and big, bulky muscles and running a marathon,” he says. “It’s you have a good fitness level and where your heart rate gets into a good zone.”

3. Be patient.

Another reason you may not be meeting your goals is that you expect to achieve them too quickly. “This is something that [people] are going to need to work on for the rest of their lives,” Johannsen says. “Diet and exercise aren’t a three-month fix-all.” Indeed, Milkovich says, people often train too hard, too fast, and then plateau too quickly. “If you start at your max, you can’t go anywhere,” he says. “You have to start slow and low and build up over time and make changes when your body is ready for them.”

Any company that advertises being able to tell you what type of diet and exercise works for you based on, say, a blood sample should also be approached with caution, Johannsen adds. “They have an agenda and they base your [recommendation] on one molecule … when the human body is incredibly complex,” he says.

4. Experiment.

If you truly want to experience physical changes from fitness and other lifestyle habits, try to identify what’s holding you back, be it your diet, exercise routine, sleep schedule, stress level, genetics, metabolism, schedule, hormones, exercise history or, most likely, some combination of factors, experts say. While the best way to do that is to work with nutrition and fitness professionals, you can also assess your strengths and weaknesses by altering one part of your lifestyle, like the intensity of your exercise routine, and monitoring the results before trying to change something else, Putnam suggests. “You have to treat your body like an actual science experiment,” she says.

Perhaps the best information you can get out of such experiments is what type of exercise you most enjoy, says Nathan DeMetz, a personal trainer in Goshen, Indiana. “Maybe they’re responding [to their fitness program] initially, but then they’re not engaged in it so they become non-responsive,” he says. “We need to create a program they enjoy.”

5. Change your mindset.

For Sharrow, the motivation to overhaul his fitness and diet regimen came from within. “I had come to the conclusion that nothing changes if nothing changes, so I was willing to make some dramatic adjustments,” he says. Fortunately, he learned those adjustments were sustainable since he now works out less and eats more satiating foods. “It doesn’t take a lot of additional work,” he says, “but a change in mindset.”

[See: Psychological Tricks to Get You Through a Workout or Race.]

Putnam agrees that body transformations only happen after mental ones. “Be honest with yourself about your readiness to change and what your objective is,” she says. “[Otherwise,] you’re going to be a non-responder.”

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Are You an Exercise ‘Non-Responder’? originally appeared on usnews.com