We’ve been taught that the more you exercise, the more calories you burn—and the more fat you lose. But Herman Pontzer’s research tells a different story. His work on constrained energy expenditure shows that humans operate within a relatively fixed daily energy budget, no matter how much we move.
In other words, when you crank up your physical activity, total energy expenditure doesn’t increase linearly. Instead, the body reallocates resources to stay within its set limit. What gets sacrificed? Things like muscle repair, hormone production, immune function, and even NEAT (non-exercise activity thermogenesis).
So while it feels like you're doing more, your body is quietly cutting corners to compensate. You burn calories during the workout—but recover less afterward. Hormones take a hit. Metabolism adapts. And the stress signals may even lead your body to shed muscle and hold onto fat.
The result? A system that’s overworked, under-recovered, and not nearly as efficient at changing your body as you hoped.
Your body isn’t trying to sabotage you—it’s trying to survive. But it can’t tell the difference between overtraining and famine. So it shifts into conservation mode, doing what it must to protect itself.
You thought you were being productive. Your body thought it was under threat. And it responded accordingly.