Running Coach Jason Karp on Three Metabolism Myths

The running guru on his latest book, myths about metabolism and a killer 14-minute cardio workout.

When author and fitness coach Jason Karp discovered running in the 6th grade, he was placed on a path that would inform not only his career choice, but his life’s true passion. Karp, who holds a PhD in exercise physiology, is the creator of Run-Fit and Revolution Running, and has written more than 400 articles and eight books—including his latest, “14-Minute Metabolic Workouts: The Fastest, Most Effective Way to Lose Weight and Get Fit,” which hits bookshelves and Amazon today.

“I wanted to address the ‘lack of time’ excuse that people use for not exercising,” says Karp regarding his motivation for writing his new book. “As a competitive runner, I’ve spent much of the last 30 years appreciating the impact that short workouts can have, and creating workouts that can make people extremely fit in a short time.”

We asked the running guru to share one of his cardio workouts, as well as bust some myths about metabolism, using wisdom from his previous book, “Run Your Fat Off.”

Myth #1: Resistance training increases resting metabolic rate.

Karp: “I often hear personal trainers tell their weight-loss clients that they have to do resistance training to increase muscle mass because muscles are ‘fat-burning machines.’ If you want to lose weight, they say, the increase in resting metabolic rate will help you burn more calories all day. Perhaps the biggest myth in the fitness industry is the issue of resistance training increasing resting metabolic rate by increasing muscle mass, which leads to greater weight loss.

“Although it is true that resting metabolic rate is influenced by the amount of muscle you have, you would have to add a lot of muscle to significantly impact your resting metabolic rate. It’s not like you can add 10 pounds of muscle (which is very difficult to do unless you train like a bodybuilder for many months) and all of a sudden your resting metabolic rate is double what it was before. Most research shows about a 10-calorie increase in metabolic rate for every pound of muscle. So, if your resting metabolic rate is 1,500 calories per day, you would need to add 15 pounds of muscle mass to increase it by 10 percent.

“Resistance training can make you look better because of the effect it has on your muscles, but it won’t really impact your resting metabolic rate much. As you lose weight, your resting metabolic rate actually decreases, even when you maintain muscle mass by resistance training. Some research has shown that exercise can prevent the decline in resting metabolic rate as you lose weight, but no research shows that resting metabolic rate increases as you lose weight. Resting metabolic rate—the amount of energy you need to stay alive—is pretty stable, having been set by millions of years of evolution. Lifting dumbbells in a gym or doing burpees in the park is not going to change that. Research has shown that metabolic rate can be acutely raised in the hours after a workout while you recover, especially if the workout is long and/or hard. However, an increased resting metabolic rate is not a chronic adaptation to exercise training. Some studies have shown an increase in resting metabolic rate following many weeks or months of exercise, but the magnitude of change is relatively small (about 30 to 142 calories per day compared to what is needed for weight loss). And some of these studies have been done on seniors, who are more likely to show increases in resting metabolic rate due to the attenuating effect of exercise on age-associated losses in muscle mass. It’s much easier to impact muscle mass, and thus resting metabolic rate, in an older person than in a younger person.”

Myth #2: Intense workouts contribute to weight loss by burning more calories after the workout is over.

Karp: “ Ever since the fitness industry found research showing that people burn calories after they work out while they recover, a whole new argument was born. Exercise stopped being about the exercise and became about what came after. ‘Do this workout,’ trainers and gurus would say, ‘because you’ll burn four times as many calories for up to 48 hours afterward.’ Oh, if burning calories and losing weight were only that easy.

“After some workouts—specifically those that are intense or long—you continue to use oxygen and burn calories because you must recover from the workout, and recovery is an aerobic, oxygen-using process. This increased oxygen consumption following the workout is called the excess post-exercise oxygen consumption (EPOC). Many studies have documented the EPOC and compared it and its associated post-workout calorie burn between exercise of different intensities and durations. However, the post-workout calorie burn caused by the EPOC is a highly exaggerated issue among fitness trainers. The increase in metabolism is transient, perhaps lasting a few hours, depending on how intense the workout was.

“The unbridled optimism regarding the EPOC in weight loss is generally unfounded. Studies have shown that the EPOC comprises only 6 to 15 percent of the net-total oxygen cost of the exercise, and only when the exercise is very intense. Since unfit individuals recover more slowly than fit individuals, the EPOC will be higher in unfit individuals. However, most unfit individuals simply can’t handle the intensity of exercise that is required to induce a high or prolonged EPOC. The calories you burn when you work out have a greater effect on your body weight than the calories you burn afterward. It is the workout itself that creates the demand for change.”

Myth #3: Thin people have a faster metabolism.

Karp: “Try this experiment: Hold five copies of my book in one hand and one copy in the other. Which arm is doing more work to hold the books? In which arm is metabolic rate faster? Did you answer correctly?

“Just because I’m thin doesn’t mean I have a fast metabolism. Heavier people actually have a faster metabolism because it takes more energy to support a heavier weight than it does to support a lighter weight, just like holding five copies of this book in your hand takes more energy than holding one copy.

“When it comes to expending energy, body weight matters. As Isaac Newton’s second law of motion (the Law of Acceleration) tells us, an acceleration is produced when a force acts on an object and is equal to that force divided by the object’s mass. The greater the object’s mass, the more force is required to get it moving. This is why a heavy person uses more calories doing the same exercise at the same intensity than does a light person.”

Treadmill hill workout

Here is Karp’s calorie-torching, 13-minute workout to try the next time you’re at the gym. Your working periods will be near the maximum rate of perceived exertion (RPE)—a 9 out of 10.

Treadmill Triple 3 Hills
3 reps, 3 minutes, 3% grade

Use the same workout speed for each rep and the same recovery speed for each recovery interval. For the reps, choose a speed that is challenging. For the recovery intervals, decrease the speed to a slow jog that enables you to recover before the next rep.

Photo credits (top to bottom): shironosov, Thinkstock; courtesy of Jason Karp