Discover Mental Energy and find your best moments for focused work

Mental Energy does not remain constant throughout the day.

At one point, a difficult task may feel easy: you can keep the context in mind, make decisions quickly, and stay focused for longer. A few hours later, similar work may require noticeably more effort.

That does not necessarily mean you have become less productive or that something is wrong with the way you work.

Cognitive readiness naturally changes throughout the day, influenced by biological rhythms, previous workload, and how effectively you recover between demanding periods of work.

That is why Mental Energy is more useful when you treat it not simply as a snapshot of the current moment, but as a way to gradually understand:
during which parts of the day demanding, focused work tends to feel easier – and when it starts requiring more effort.

One of the most familiar examples of this change is the afternoon slump.

At around 2–3 PM, many people notice that a task that felt easy in the morning suddenly starts moving more slowly.
Reading feels harder.
Concentration requires more effort.
You want coffee.

Because all of this happens after lunch, food often gets blamed automatically.

But the so-called afternoon slump is more complicated than that.

Two biological processes influence alertness

Our state of alertness is strongly influenced by:
circadian rhythms, which create recurring changes in alertness across the day;
and
homeostatic sleep pressure, which generally increases the longer you remain awake.

These processes help explain why cognitive performance can change throughout the day even without a heavy lunch.

Research shows that attention, reaction time, memory, and other cognitive functions can vary depending on time of day, although the magnitude and exact timing differ substantially between people and tasks.

So when your state declines at 3:00 PM, the answer is not necessarily:
“I ate too much.”

Then your workday is added on top

Your biological rhythm is only the background.

By the middle of the day, you may already have had:
four hours of screen time;
two demanding meetings;
constant messages;
an intensive morning project;
dozens of small decisions.

So what feels like an afternoon slump may actually be the result of several processes happening at the same time.

That is why the same time of day can feel very different from one day to another.

Your circadian rhythm is relatively predictable.
Your previous workload is not.

Look for a recurring pattern

Mental Energy becomes especially interesting when you stop focusing on individual readings and start comparing days.

Over one or two weeks, pay attention to this:
Does Mental Energy tend to decline at roughly the same time?

If so, you may have identified a recurring part of your daily pattern.

Then ask a second question:
Does the decline begin earlier after a particularly demanding morning?

This is where the picture becomes much more useful.

For example, your baseline pattern may be a moderate decline after lunch.
But an intensive morning workload may shift that decline earlier.

That is much more precise than simply saying:
“I am bad at working in the afternoon.”

Use the pattern before it happens

Once you begin to recognize a recurring window of decline, you can experiment.

Avoid scheduling your most demanding work during periods when Mental Energy is usually Low.
Use that time for routine tasks.
Or schedule recovery before your usual decline becomes pronounced.
Then compare the result.

Your state is not supposed to be identical at 9:00 AM, 2:00 PM, and 6:00 PM.

The goal is not to eliminate natural fluctuations in Mental Energy. It is more useful to learn to anticipate them.

If you notice a similar decline at roughly the same time for several days in a row, stop planning that period as though the pattern does not exist.

Move demanding tasks closer to your stronger periods, and schedule recovery before your usual decline rather than after it.