This Is Why You Feel Tired After Sitting Down At Work All Day

Have you ever gotten home from work at the end of the day and wondered, “Ugh, why does my body ache so much? All I was doing was sitting at my desk!”? That’s what Katie Heaney at Science of Us found herself asking recently, so she looked into it — and it turns out there’s a reason for why you feel tired after sitting down at work all day. In fact, as I dug a little further, I found that there are a number of possible culprits for your workday exhaustion, even if your job is a desk job. Here’s what science has to say about it.

Heaney started by speaking to Lenox Hill Hospital’s director of sleep medicine, Dr. Steven Feinsilver, who explained that mental fatigue is just as taxing on the body as physical fatigue is. “Your heart will pump and you’ll produce adrenaline whether somebody’s chasing you, or you just really upset about something,” he said. It has to do with how much oxygen (read: energy) your body requires to do certain things — and it turns out that your brain needs a lot. Said Feinsilver, “Your muscles normally aren’t sucking a lot of oxygen out of you. With exercise, they will. But the brain always takes a lot of your energy.” So, if your desk job involves a lot of thinking, problem-solving, or other brain activity, then that could be the source of your work-based fatigue.

There’s research to back this idea up, too: A study published in the Journal of Applied Physiology in 2009 found a link between mental fatigue and perceived physical exhaustion. For the study, the researchers had 16 participants ride stationary bikes under two conditions: One in which they were mentally rested, and one in which they were mentally fatigued. (Physically, the conditions were the same each time — they slept the same amount before each trial, as well as drank the same amount and ate the same meal beforehand.) During the condition in which they were mentally rested,the participants watched neutral (which I'm taking to mean "non-mentally-taxing") documentaries for 90 minutes before hopping on the bike; during the one in which they were mentally fatigued, though, they spent 90 minutes performing tasks involving paying close attention, remembering things, and reacting quickly.

Although there was no difference between the trials in how the participants’ hearts or muscles performed, they stopped biking on average 15 percent sooner, citing physical exhaustion, when they went into the exercise session mentally fatigued. It’s true that the study was small; more research is certainly requited before we can draw any wide-reaching conclusions from it. But the link is fascinating, and may go some way towards explaining how we can feel tired without having expended physical energy.

Of course, what actually happens to your body when you sit for long periods is also part of the equation. You’ve probably heard that sitting too much is slowly killing us all, right? Well, it’s true: Spending as much time sitting as many of us do is, uh, not doing terrific things for our health. As AsapSCIENCE detailed in a video from 2015, a bunch of things happen immediately when you sit down: The electrical activity in your muscles drops,and the rate at which you burn calories drops to about one calorie per minute. After three hours, your artery dilation has decreased, making blood flow a lot slower. The effects compound dramatically over time, and what it all adds up to is… early death. Awesome.

I also found this of interest: Summarizing work done by Dr.James Levine of the Mayo Clinic, Peak Fitness notes, “When you’ve been sitting for a long period of time and then get up, a number of molecular cascades occur. For example, within 90 seconds of standing up, the muscular and cellular systems that process blood sugar, triglycerides, and cholesterol — which are mediated by insulin — are activated.” When these systems are activated regularly, you get a ton of health benefits from them, like a decreased risk of diabetes. Indeed, says Peak Fitness, “your body was designed to be active and on the move all day long” — we’re meant to be moving around a lot. But when these systems not activated regularly, your body interprets it in some pretty gnarly ways. “When you stop moving for extended periods of time, it’s like telling your body it’s time to shut down and prepare for death,” writes Peak Fitness.

Not going to lie: I’m really curious if that whole “OMG sitting down a lot makes my body think it’s time to die” thing is also contributing to why I feel so tired after a workday spent sitting down.

There are some other possible culprits, too, of course; as Healthy Way notes, both light deprivation and “Sick Building Syndrome” (which is, amazingly, a technical term) can also contribute to feelings of physical fatigue. But the good news is that, no matter the cause, it can all be treated the same way you’d treat general office torpor: By making an effort to move around a bit more. If you get one of those standing desks that lets you adjust its height easily, you can move back and forth between sitting and standing at various points throughout the day; every half hour or so, you can stand up, stretch, walk across the office and back, or do some knee bends; heck, you could even spring for a treadmill desk if that’s doable for you and/or your office.

Oh, and don’t forget to drink a lot of water; sitting down a lot has a tendency to dehydrate us. Katie Heaney at Science of Us even has a strategy for making sure you’re both drinking enough water and moving around during the day: “There’s an easy way to make these breaks go hand in hand, too,” she notes. “Drink as much water as you should, and you’ll have to get up from your desk (or couch) at least once an hour to use the bathroom. Whatever you’re working on will still be there, unfortunately, when you get back.” Sad, but true.