Total daily energy expenditure remains within a narrow range regardless of variations in physical activity levels.

Study: Effect of Exercise Intensity on Spontaneous Physical Activity Energy Expenditure in Overweight Boys: A Crossover Study

Even when these boys exercised more, their bodies moved a little less afterward, so they didn’t burn much more energy overall — suggesting our bodies try to keep daily calorie burn pretty steady.

Study: Deciphering the constrained total energy expenditure model in humans by associating accelerometer-measured physical activity from wrist and hip

When adults walk a lot, their bodies naturally move their arms less — like fidgeting less — so their total energy burn doesn’t go up much. This means even if you exercise more, your body might just cut back elsewhere to keep your daily energy use about the same.

Study: Energy balance in cyclists on plant‐based diets during a 30‐day, 4300‐km ride across Canada: Two case studies

Even when these cyclists rode much more or less each day, their total daily energy burn didn’t change as much as you’d expect — their bodies seemed to adjust internally to keep energy use fairly steady.

Study: The evidence for constrained total energy expenditure in humans and other animals.

Even when people exercise more, their bodies burn about the same total amount of energy each day because they automatically use less energy elsewhere—like slowing down metabolism a bit. So, extra exercise doesn’t mean you burn way more calories overall.