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Yes, Being Mentally Tired Is Physically Exhausting

Ever felt like you ran a 10k after a stressful day sitting at a desk?

Being a journalist, I perform close to zero physical labor over the course of a workday, and yet, I’m utterly exhausted by the time I take my 50th step of the day out of the office, craving nothing more than to sink into my couch and let the TV hypnotize me to sleep.

But why am I so drained, when the only muscle I’m actually straining throughout the day is my brain? According to a paper published in the 2014 issue of Personality and Social Psychology Bulletin, it’s because mental energy really does translate to physiological energy.

To prove this, researchers measured how long college students could squeeze a metal hand grip (a task commonly used in psychology experiments to measure physical effort). The students also underwent a baseline blood pressure measurement. Next, the students were told that they were going to write a graduate admissions essay (which they were never actually made to write, but they didn’t know that yet). Afterward, some of the students performed what’s called a mental contrast exercise (that is, they focused first on how writing the essay would make them feel in the future, then considered where they were currently in relation to that goal).

After the exercises, the students had their blood pressure taken a second time and squeezed the hand grip again. Researchers found that when subjects felt the task (writing the essay) was extremely difficult, their blood pressure went down, but when they thought it was highly achievable, it went up. Those who found the task daunting also held the hand grip for less time than they had during the baseline test, while those who thought it was a piece of cake held it for a longer period of time.

What all of this suggests is that getting mentally energized to achieve a goal creates physiological energy (and vice versa). L.A.-based psychologist and psychotherapist Jeanette Raymond explains this mental energy in more relatable terms: “It might be helpful to think of mental energy as attention, focus, concentration and emotional state,” she says. “Think of feeling wiped out, slouched on the couch. Then your friend calls and asks you to go out to a strip club. For some, this would immediately energize them mentally — the dopamine receptors in your brain would be activated, because it provides a reward (hanging with friends and being sexually titillated).

“On the other hand, if your partner asks you to fold laundry, something that can feel like a duty, your brain will give you a sensation of having to pull blood out of stone — it’s not rewarding, so you won’t feel energized. In fact, it will make you feel drained.”

So is it possible to increase your mental energy (and therefore, physical energy)? “Mental energy is an emotional state dependent on reward and motivation,” Raymond emphasizes. “It’s not about increasing it, per se — it’s about finding the right activities that feel rewarding, which will offer instant energy.”

All of which explains why I have apparently limitless energy when running through the streets, wasted, at 2 a.m. (an activity that feels immensely rewarding, at least at the time), but zero energy when drowning in a seemingly endless stream of work emails on Sunday morning.

Although maybe that’s just the hangover.