Why sitting at your computer all day can wipe you out

Certain forms of tiredness can often feel more “earned” than others. I get being tired after a run, but after sending some emails? Come on. Yet Dr. Steven Feinsilver, the director of sleep medicine at Lenox Hill Hospital, stresses that mental fatigue is very much legitimate. He explains that the human body reacts to stress in many of the same ways regardless of whether the source is mental, like a difficult math problem, or physical, like running. “Your heart will pump and you’ll produce adrenaline whether somebody’s chasing you, or you’re just really upset about something,” he said. Furthermore, the brain requires a disproportionately high amount of the body’s energy, accounting for about 20 percent of the oxygen consumed by the body. “Your muscles normally aren’t sucking a lot of oxygen out of you,” says Feinsilver. “With exercise, they will. But the brain always takes a lot of your energy.” In other words, if you’re conscious, your brain demands your energy, and lots of it. Using your brain takes real, honest, physical work — it’s just not visible to us the way using our muscles to exercise is.