Thinking Hard Burns Almost No Calories—But Destroys Your Next Workout
Hacker News
February 17, 2026
Your brain uses 20% of your body's energy just idling. Intense thinking barely adds to that. But the mental byproducts of a long cognitive day quietly sabotage your endurance in ways no amount of willpower can fix.
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Originally published on Hacker News on 2/17/2026