Our bodies send us clear signals when we need a break.
Fidgetiness, hunger, drowsiness, loss of focus.
Mostly, we override them.
We find artificial ways to pump up our energy: caffeine, sugary foods, and our body’s own stress hormones — adrenalin, norepinephrine, and cortisol.
A much smarter way would be to work with something we all have at our disposal:
Our ultradian rhythms.
These rhythms exist in all of us, and we can leverage them as a way to engage in focused bouts of deep work.
This is not just another productivity fad. It is a biological fact that we are optimized for focus and attention within these 90–120 minutes cycles.
In his first Premium AMA, Stanford professor Andrew Huberman spoke at length about how he uses ultradian cycles to manage his day and best capture neuroplasticity (even on the weekends!).
In this post, I describe everything I’ve learned about ultradian cycles, how they work and how I personally plan on applying this to my life (definitely not on the weekends!).
The Science Behind Ultradian Rhythms
Most of our body’s essential processes run on a 24-hour cycle called a ‘circadian rhythm’.
Circadian = “about a day”
On a coarse level, the circadian rhythm manages the transition between wakefulness and sleep. In addition, it regulates fundamental processes like our body temperature, blood pressure, hormones, hunger, and digestion.
On a finer level, but just as important, are the shorter ‘ultradian rhythms.’
These are the biological rhythms that are repeated throughout a 24-hour day and therefore have a shorter period and higher frequency than a circadian rhythm.
Ultradian = “many times a day”
In the context of performance and focus, the most important ultradian rhythm is the 90-minute cycle.
In the 1950s, sleep researcher Nathaniel Kleitman discovered that the human body moves through 90–120 minute cycles — from the day we’re born to the day we die. He called it the “basic rest-activity cycle.”
At night, these cycles correspond to the different stages of sleep (alertness, light, REM, deep, etc.). All night we go through these repeating rhythms.
Kleitman also found the 90-minute pattern in our days, as we move from higher to lower energy and alertness.
Now, you might have heard about “energy management over time management” before.
To some people, that might sound like just another productivity fad.
However, the research here is undeniable:
Biologically, we are optimized for focus and attention within these 90 minutes cycles. This applies to cognitive work (writing, language, music) as well as skill learning (dance, how to perform an athletic move).
These rhythms exist in all of us, and if you care about deep work, you should leverage them as a way to engage in focused bouts of mental work.
Unfortunately, most of us override these naturally occurring rhythms to the point that they no longer penetrate conscious awareness.
Your body was designed to work in sprints followed by breaks, not constantly throughout the day. Trying to push yourself to focus for 3–4 hours on end, while possible, is not in line with what is known about the underlying biology.
If you know how to tap into your body’s ultradian rhythms, you can get more done by working when your body is at its best and then recharging when you need it most.
So, the first key questions here are:
How do you apply this to your life? And how do you know when to start a 90-minute learning bout?
Tapping Into Your Ultradian Rhythms
There’s good news and bad news.
Bad news first?
Ultradian cycles are “about” 90–120 minutes. You could wake up (naturally or by a noise) in the middle of an ultradian cycle. That cycle continues even if you wake up in the middle of it.
So ideally, you don’t wake up and immediately throw yourself into focused work.
But here’s the good news:
You can figure out when your first proper ultradian cycle of the day begins simply by asking yourself:
“When am I most alert after waking?”
Observe yourself for a few days. Look out for when you have your peak levels of physical and mental energy, given your standard intake of caffeine and exercise:
- In the morning: between waking and noon
- In the afternoon: between noon and bedtime
Here’s how Huberman describes a hypothetical example:
Let’s say that you wake up at 7 am. You’re in the middle or towards the end of an ultradian cycle — it doesn’t really matter.
Typically you’ll find that for the first hour after waking up; you tend to feel a bit groggy. But then you notice that your attention and alertness peak around 9.30–10 am.
You can be pretty sure that the first ultradian cycle for learning is going to be optimal to start at about 9.30–10 am.
These cycles are triggered by fluctuations in the ‘glucocorticoid system’ — the system that regulates cortisol release.
Even though cortisol is often seen as a terrible thing, it is essential for health. Every day we get a rise in cortisol in the morning, associated with enhanced immune function, alertness, and focus.
Across the day, the baseline jitters a little bit. The cortisol level comes down but bounces around. It’s not a flat line. Each one of those bumps corresponds to a shift in ultradian cycles.
(Quick shout-out to the #1 protocol Huberman is consistently reinforcing: get sunlight in your eyes as close to waking up as possible. It increases the peak level of cortisol experienced early in the day.)
If you find you are most alert around 9.30 am and typically have a peak of focus and concentration around 10 am — that is valuable information.
In that case, Huberman recommends starting your first bout of focused work between 9.30–10.00 am. Then, you have about an hour to get the maximum amount of deep work in.
You do the same for the afternoon.
Now, this will be different for everyone — both in terms of timing and how many of these bouts you can do.
For the average person, 1–3 x 90-minute intervals per day are typical. It depends on how well you’ve slept, how well you’re nourished, and how trained your focus capacity is.
4 x 90-minute blocks of focused learning per day, while possible, is highly unusual.
Some people here might think: “This is silly. I can go on for hours. Plus, working for only 3 hours per day is unrealistic. My job needs me to be behind my computer for at least 10 hours.” I hear you — that was my initial reaction as well.
We’re talking here about ‘deep’ work requiring high focus and concentration levels. Not any kind of work, like replying to e-mails.
We’re also talking about working in a way that neuroplasticity. Anyone can stare at a screen for 10 hours. But is it triggering long-term brain change?
Anyway, more on this in a moment.
The Composition of 1 Focused Bout
Now, this is important because according to Huberman, there’s quite a bit of confusion around how these 90-minute cycles work.
We don’t get the entire 90 minutes of peak performance focus.
It takes about 5–15 minutes for most people to break into a deep focus. See it as a warm-up.
Then you have about an hour to maximize learning. That’s your peak of high performance. Even though it’s an ultradian 90-minute work block, neuroplasticity will be best triggered within the 60 minutes portion of that. There’s no way to know precisely when that 60 minutes begin and end until you start the work block.
Occasionally, your focus will flicker. That’s perfectly normal. The key is to continuously shift back your focus. That’s an active process and requires a lot of metabolic energy, so it’s important to get rid of all possible distractions around you.
(Low-hanging fruit: phone out of the room! By having your phone in your field of view, your brain must work hard to ignore it. It’s a waste of precious energy.)
Your body and brain are burning through a significant amount of oxygen, glucose, and other energetic fuels so towards the end of the cycle, there’ll be some taper. And then you’re out of the work block.
You rest. And this is key.
Improving your ability to focus is not just related to what you do during the focused bout. It’s just as dependent on what you do after the focused bout.
Prioritize Breaks and Sleep
20 minutes is ideal, but any break (even 5 or 10 minutes) is better than nothing.
You don’t need to sleep or stare at the ceiling. You can do something functional to your day but you just need to let your mind wander for a bit. Do things that are automatic and reflexive for you.
Avoid focused reading or anything that requires a screen.
Try and deliberately decompress because that will allow you to drop into intense bouts of focus again and repeatedly throughout the day.
If you ignore your body’s signals and drag yourself through these low-energy dips, your energy and focus will eventually crawl out of the ultradian dip and return to a somewhat higher level of functioning — but not nearly as high as before. You’ll get work done but not nearly as much or nearly as well (and you’ll feel like crap by the time you’re done).
And lastly, probably the biggest secret of all:
Accessing the state of neuroplasticity happens during waking states.
But the actual rewiring and reconfiguration of our neural circuits occur during sleep and deep rest.
This is excellent news because it fundamentally means that there is no point in trying to engage your brain at maximum capacity at all times or sacrificing sleep to get stuff done.
The truly valuable skill here isn’t the capacity to push yourself harder but to stop and recuperate despite the discomfort of knowing that work remains unfinished, emails unanswered, other people’s demands unfulfilled.
Here’s What I’m Taking Away From All of This
Whether you're asleep or awake, your entire existence occurs in these cycles.
They’re so crucial to learning and memory that Huberman applies these ultradian bouts every day — even on the weekends.
On off days, the learning bout might be around something more casual, like reading a book, but he’s still keeping in mind the 90-minute cycle.
Here’s why he does this:
The neural circuits for focus are themselves responsive to neuroplasticity. So the more you work on focus, the easier focus gets.
Now, I’ll be honest. I’ll do my best to be more aware of the above but I don’t want to become too obsessed either. Some days I feel like I can start immediately after waking up; other days, I need time to get into it. Some days I can write for 2 hours; on others, I lose focus after 15 minutes.
I do see the value of understanding how these cycles work and being hyper-aware of them.
So there are a few important takeaways for me and how I’ll approach work moving forward:
1/ Know when to stop. Often when I feel like I haven’t “achieved” enough, I force myself to power through even though I’ve clearly hit the point of Diminishing Returns. (Law of Diminishing Returns — after a certain point, the additional work you put towards a project returns less and less until the return eventually becomes negative (more work = a worse outcome). For example, spending 4 hours writing a newsletter will make it good, but will spending 8 hours make it twice as good? Or 12 hours 3 x as much?)
So, even though you feel like you can do more work, take a break. Salman calls it Creative Leftovers. Let your subconscious mind do some work now.
2/ Take REAL breaks. Taking breaks feels so counterintuitive, especially when I feel like “I’m on a roll.” But knowing the basic science behind neuroplasticity and how crucial it is to give my brain a rest, I make sure I take proper breaks. In the morning, I’ll write down a list of menial tasks I can do between bouts of focused work. Put laundry away, call X, do the dishes, quick supermarket run, etc. Anything to get me up and moving.
3/ Removing distractions is vital. Protect your working bouts. The slightest distraction can pull you away from your focus. The key one here is just keeping my phone out of my sight.
4/ Be patient. It takes 10–15 minutes to get into deep focus. If you know that, it’s easier to stick with the task and resist walking away because “you’re not feeling it today.” You just need to get past that hump.
5/ You’re not lazy. There are days when I don’t get anything done. I can be really hard on myself for those. It’s important to internalize that slowing down and feeling low energy isn’t me being “lazy” or “undisciplined.” It’s simple biology that our bodies go through cycles with varying energy levels throughout the day.