AFFECTIVE FACTORS ON THE AMOUNT OF CALORIES YOU BURN

If you've ever attended a group exercise class where the estimated number of calories burned and each person's heart rate are shown on a screen, you are aware of how individual these numbers can be. It's also likely that you've noticed that men typically burn more calories than women. Have you ever wondered, though, why, even during the same workout, different people burn calories at such disparate rates?

In actuality, metabolism—a catch-all word for all the bodily functions that facilitate growth, release energy from food, and more—is a complex process. According to functional medicine specialist Anya Rosen, "there is a constant ebb and flow of reactions that build or repair our body (anabolism) and reactions that break down food and energy stores for fuel (catabolism)." There are several factors that determine how quickly or slowly you burn calories at any given moment. These are the five that, according to experts, have the biggest effects on how many calories you burn when exercising.

1. Weight of Body

As a general rule, you will burn more calories per session the heavier you are, according to Kyle Gonzalez, head of content for a supplement company. "Since calories are merely a measurement of energy, moving your body requires more energy if you weigh more." Stated differently, the heavier of the two will burn more calories during a given amount of movement because they will be expending more energy.

Because larger internal organs require more energy to operate, people with larger bodies also typically have larger internal organs. This has a big impact on how many calories are burned both at rest and during exercise. One of the numerous reasons weight loss is so difficult is that when your weight drops, your body starts burning fewer calories, which can cause a weight loss plateau or even weight gain.

2. Mass of Muscle

This is where things become a little more difficult. A person who weighs the same but has less muscle will burn fewer calories than a person with greater muscle mass. Sports nutritionist Jenaed Brodell claims that muscle tissue burns calories more efficiently than fat tissue.

Since your body must use more energy to support the increased rate at which your muscles are contracting during exercise, having more muscle mass will increase your total caloric burn. To put it another way, thinking about increasing your strength-training regimen could help you improve your calorie burn.

3. Age

According to Brodell, "we tend to lose muscle mass as we age." "You can lose up to 3 to 5 percent of your muscle mass every decade after the age of 30." Although the exact causes of this are unknown, one review suggests that it most likely stems from your body growing more immune to the hormones that support the synthesis of proteins, which is essential for maintaining muscle mass. Your metabolic rate, or how quickly you burn calories both at rest and when exercising, is lowered as a result of this loss of muscle mass.

Gonzalez argues that regular strength training can help you maintain or even increase your muscle mass, even though you cannot stop your body from aging. "You can burn more calories at rest by increasing your resting metabolic rate with strength training." 

4. Level of Fitness

Exercise becomes easier the more of it you perform. Gonzalez clarifies, "That's not in your head; over time, your body does adapt to do things more easily." In general, this is advantageous. It means that with practice, you can run farther or faster, and with the right training, your muscles will be stronger enough to lift larger weights.

But your calorie burn is also impacted by it. "You will burn less calories with the same workouts as your body adjusts to training," says Gonzalez. "As you get fitter, your body becomes more efficient—from your lungs to your muscles to your heart to your brain." Because of this, a beginner may burn a lot more calories than a person who has been working out consistently for years.

5. Intensity of Training

Additionally, it's possible that two persons performing the same exercise are burning different amounts of calories because they aren't performing the same exercise. According to Brodell, a person can burn twice as many calories in the same amount of time exercising at a high intensity—that is, until you are breathing heavily and are unable to carry on a conversation.

In the end, there are many advantages to exercise beyond merely burning calories, so the most crucial thing is to choose activities that you enjoy and can continue. "A person's goals, level of physical fitness, and abilities ultimately determine what kind of exercise is best for them," adds Brodell.