When you’re racing 90 miles an hour, the last thing you want to do is slow down.

That’s how it feels on those exhilarating days when you’re completely focused, tearing through your to-do list, racking up accomplishments. You just want to keep going.

You might also worry that if you take a break, you’ll lose momentum and find it impossible to regain your stride.

But the research tells us otherwise. Studies show we have a limited capacity for concentrating over extended time periods, and though we may not be practiced at recognizing the symptoms of fatigue, they unavoidably derail our work. No matter how engaged we are in an activity, our brains inevitably tire. And when they do, the symptoms are not necessarily obvious. We don’t always yawn or feel ourselves nodding off. Instead, we become more vulnerable to distractions.

Consider what happens over the course of a typical day at the office. The early morning hours are when most of us are at our sharpest, but as the day wears on, we inevitably lose steam. And it’s at this point that we become more easily seduced by the lure of viral videos, celebrity gossip, and social media. A recent study examined the time of day Facebook users are more likely to post updates. The finding? Facebook usage builds from 9:00 AM through noon, dips slightly during lunch, and then peaks at 3:00 PM, the precise hour when many of us are at our most fatigued.

While tiring over the course of the workday can’t be prevented, it can be mitigated. Studies show that sporadic breaks replenish our energy, improve self-control and decision-making, and fuel productivity. Depending on how we spend them, breaks can also heighten our attention and make us more creative.

A 2011 study published in Cognition highlights another upside to sporadic breaks that we rarely consider: goal reactivation. When you work on a task continuously, it’s easy to lose focus and get lost in the weeds. In contrast, following a brief intermission, picking up where you left off forces you to take a few seconds to think globally about what you’re ultimately trying to achieve. It’s a practice that encourages us to stay mindful of our objectives, and, as the authors of the study report, reliably contributes to better performance.

The challenge, of course, is finding the time to step away for 15 minutes, or—even when we have the time—getting good at dragging ourselves away from our computers preemptively, before we’re depleted. One approach that can help involves blocking out a couple of planned 15-minute intermissions on your calendar, one in the mid-morning and the other in the mid-afternoon.

Next, find something active you can do with this time and put it on your calendar. Take a walk, stretch while listening to a song, or go out with a coworker for a snack. If these activities strike you as too passive, use the time to run an errand. The critical thing is to step away from your computer so that your focus is relaxed and your mind drifts. (So no, checking Facebook does not count.)

Finally, note your energy level when you return. You are bound to feel invigorated, both because you’ve allowed your brain some rest and because the physical movement has elevated your heart rate.

If this feels like a dereliction of duty, remind yourself that the human brain was not built for extended focus. Through much of our evolutionary history, heightened concentration was needed in short bursts, not daylong marathons. Our minds evolved to snap to attention when we encountered a predator, keeping us vigilant just long enough to ensure our survival. Yet today, we expect far more from ourselves than centuries of evolution have designed us to do.

Ultimately, the question we should be asking is not whether breaks are worth taking – we know they are. It’s how we can better ensure that they actually take place.