Your body is constantly burning calories, whether or not you're working out. The number of calories you burn every day just to function normally is called your resting metabolic rate. The higher this number is, the easier it is to burn fat. Unfortunately, your metabolism is extremely hard to control—even exercise has little effect.
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Resting Metabolic Rate
Most cardio machines have display monitors that show how many calories you've burned during your workout. Sometimes it can be daunting to watch the number rise so slowly, but the truth is that burning calories during exercise takes a lot of time and effort.
Thankfully, your workout isn't the only time during the day that you burn calories. In fact, you probably burn more throughout the day from simply resting than you do during your workout. Your resting metabolic rate is the amount of energy you burn throughout the day while sitting or lying down and resting. For many adults, the number is between 1,000 and 2,000 calories per day.
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Think of that number as your set point. It doesn't change very much day in and day out, regardless of what you do. While a workout makes you burn energy, it doesn't affect your resting metabolic rate very much.
Researchers typically measure resting metabolic rate in the morning, when you're not very active. Wait at least 12 hours after your most recent workout, so that your body is in a relaxed state.
Workouts do ruffle the feathers of your metabolism slightly. After a workout, you continue to burn calories slightly higher than you would at rest. However, that number comes down quickly, and you return to normal. Even as your fitness levels improve and you ramp up the intensity of your cardio workouts, the set point of your metabolism hardly changes.
One reason for the lack of change may be that cardio workouts help you burn energy, which in turn burns fat. According to a 2012 study published in Obesity, subjects who went on a diet and lost weight saw reductions in their resting metabolic rate. Losing weight seems to lower your metabolism, which means that if your cardio workouts are burning fat, they could, in turn, be lowering your metabolism.
The Effect of EPOC
Cardio doesn't seem to have much of an impact on your metabolism overall, unlike weight lifting, which could bump up your metabolism by adding muscle mass to your body. However, cardio workouts throw researchers for a loop because there seems to be increase in your metabolism during and for up to 48 hours after your workout. This increase is known as excess post-exercise oxygen consumption.
Despite the long-winded name, it's not very complicated. Workouts burn energy, which means that your body has to recover afterward. When you stop exercising, you body has to keep working to make sure that it replenishes the energy that you lost.
Depending on how intense your workout was, your recovery time can be as little as two hours or as long as two days. During that time, you consume more oxygen than normal, which indicates that your metabolism is raised slightly. Scientists see this as something different from your resting metabolic rate, and therefore don't count it as an increase in your actual metabolism. It's temporary.
Read More: How to Raise Your Basal Metabolic Rate
Muscle and Metabolism
Some researchers speculate that gaining muscle mass can boost your metabolism. Muscle tissue is very active and needs constant refueling. If you lift weights and gain more muscle, your metabolism would theoretically rise. However, a 2017 study in Applied Physiology, Nutrition and Metabolism shows that in six months, people who lift weights don't have a significant increase in resting metabolic rate.
Unfortunately, metabolism is an incredibly complicated topic, and there is rarely a cut and dry answer. Muscle mass is important for your resting metabolic rate, according to a 2013 article published in Cell Metabolism. According to the authors, muscle mass accounts for about 30 percent of your metabolism. Therefore, if you increase your muscle mass, your metabolism should rise—but the change won't be monumental.