Think You Have More Energy To Give? Your Brain May Disagree

Author: Zhané SlambeeOctober 06, 2026mindbodygreen editorBy Zhané SlambeeImage by Marc Tran / StocksyOctober 06, 2026It’s 3 p.m. and instead of hitting your usual afternoon slump, you’re flying.

Your inbox is shrinking, your thoughts feel quick, and the project you’ve been avoiding is suddenly getting done. You feel so switched on that stopping seems almost silly.

But a burst of mental energy doesn’t necessarily mean you have more to give. In a recent study1, researchers looked at how fatigue and mental performance changed throughout the day.

They found that both feeling more tired than usual and performing faster than usual could be followed by a lower ability to keep pushing through fatigue later on.

The researchers focused on fatigue override, or your ability to keep performing even when you feel tired. We all do this sometimes, whether we’re finishing a deadline during an afternoon slump or staying focused through a long meeting.

To study this in everyday life, researchers combined data from six studies involving 1,088 people.

Some participants were healthy, while others had chronic health conditions. Rather than testing everyone in a lab, the studies checked in with participants repeatedly throughout their normal days.

At each check-in, participants reported how tired they felt and completed a short test of processing speed, which measures how quickly they could respond to a simple mental task.

Because participants completed these check-ins more than once, researchers could compare each person with their own usual pattern.

This let them see what happened when someone felt more tired than they normally did or performed faster than they normally did, then track how well they were able to keep going afterward.

During their normal days, participants who felt more tired than usual had a harder time maintaining their performance despite fatigue in the hours afterward.

Shop nowThe same pattern appeared after they performed faster than their usual pace on the processing-speed test. So, someone could have a sluggish moment and then have less capacity to push through fatigue later.

But someone who felt unusually sharp and performed especially well on the processing-speed test could also have less capacity afterward.

People with chronic health conditions had a lower overall ability to keep performing despite fatigue compared with healthy participants.

This doesn’t mean feeling productive is bad for you. It suggests that doing well right now isn’t always a reliable sign that you’ll have the same capacity a few hours from now.

It’s easy to use productivity as a quick check of how much energy you have left. If you’re getting a ton done, you must be doing fine.

Not necessarily. You can be performing well while your ability to keep pushing later is already starting to dip.

That makes changes from your normal pattern worth noticing.

If you’re much more tired than usual, that’s useful information. But if you’re unusually focused and flying through tasks, you don’t necessarily need to squeeze every last drop out of that momentum.

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You don’t need to interrupt every productive streak. Instead, use noticeable changes in your energy and focus as a reason to pace yourself.

The goal isn’t to avoid fatigue. It’s to notice when your usual rhythm changes and respond before you’re completely depleted.

Your ability to keep going isn’t always obvious from how you feel in the moment.

If your energy or focus feels noticeably different from normal, it may be a good time to pace yourself rather than automatically pushing harder.