It’s True, Thinking Hard Really Can Wear You Out

Science proves what we already suspected. Hard thinking really does wear out our bodies, though we can’t actually explain why.

It’s True, Thinking Hard Really Can Wear You Out

Some days, you leave work at 5 p.m. ready to pick up the kids, make a three-course meal, build a birdhouse, and hit the gym. Others, you walk in the door and collapse on the couch, begging for the sweet release of reality TV to soothe your inexplicably sore body along with a delivery pizza to fuel you up for a particularly intense eight hours of sleep.


Both days your “work” was just sitting at your desk, but one left you far more physically exhausted. Why? Well, were you thinking harder on pizza day?

Because as PopSci points out, a study headed by Samuele Marcora, a University of Kent Professor of Exercise Physiology, has proven that thinking hard really can leave your body exhausted. Researchers gave subjects one of two 90-minute tasks–one playing a mentally engaging computer test, and one watching documentaries on trains and Ferraris. Then they were asked to hop on a bike. In almost all cases, the documentary watchers were able to peddle longer than those who’d been tested by a computer for an hour and a half. And in a twist of science, heart rate, respiration, and blood glucose levels were consistent between the two groups. (Apparently, there’s no known metric for force of will.)

But there is an important lesson we can learn, reading between the lines a bit. I find it particularly notable that as subjects hopped on the bike, both groups chose the same level of resistance–mentally fatigued or not. In other words, even though the mentally fatigued had less gas in the tank, they chose to work with the same level of challenge.

It means that when we’re mentally exhausted, we won’t always titrate our workload to fit.

The study’s authors believe their findings are most important to physical jobs, like military personnel. But I imagine, there really might be something to taking a leisurely day off work before a particularly taxing conference, set of meetings, or jewel heist. At least if you want the residual energy to party properly with your coworkers later.

Read the study here.


[Hat tip: PopSci]

[ILLUSTRATION: Desert via Shutterstock]

About the author

Mark Wilson is a senior writer at Fast Company. He started, a simple way to give back every day.