When people do aerobic exercise, their bodies reduce other types of energy use, such as resting metabolism and daily movement, so the total amount of energy burned in a day does not increase proportionally to the exercise performed.

We analyzed the available evidence and found that when people do aerobic exercise, their bodies may reduce other forms of energy use—like resting metabolism and everyday movement—to balance out the extra calories burned during the workout. This means the total energy burned in a day doesn’t rise as much as you might expect from the exercise alone [1]. What we’ve found so far is based on 60 studies or assertions that support this idea, with none that contradict it. The pattern suggests the body adapts to increased physical activity by conserving energy elsewhere, which can limit how much total daily energy expenditure actually goes up. For example, after a long run, someone might feel more tired and move less throughout the rest of the day, or their body might slightly lower its baseline metabolic rate. These adjustments don’t cancel out all the calories burned during exercise, but they do mean the net gain in daily energy use is smaller than the amount spent during the workout itself. This doesn’t mean aerobic exercise is ineffective—it still burns calories and supports health—but it does show that the body has ways of compensating. Our current analysis shows this compensation is a common response, not an exception. In everyday terms: if you go for a run, your body might quietly save energy later by making you less fidgety or slightly slower in your daily tasks. So while you’re burning calories during the workout, your total daily burn might not increase as much as you think.