90-minute work blocks and the ultradian rhythm

the problem with rigid schedules (and maybe your brain)

you've tried the pomodoro technique, right? the 25 minutes on, 5 minutes off rhythm is a classic for a reason. it’s great for breaking down big tasks and getting started, especially when procrastination feels like a heavy blanket. but sometimes, just as you're really getting into a groove, that timer buzzes, yanking you out of your flow state like a sudden alarm. it can feel like a disruption rather than a helpful nudge.

for brains that thrive on hyperfocus, or those with ADHD where getting started can be tough, those 25 minutes can feel like barely enough time to settle in. pulling yourself away from deep concentration just to take a mandated break can feel disruptive and even counterproductive. it's a bit like being told to stop breathing deeply mid-lunge, just when you're finding your stride. your brain might actually need a longer runway to hit peak performance.

enter the ultradian rhythm

before pomodoro timers and productivity gurus, there was nathaniel kleitman, a sleep researcher. back in the 1950s, he identified what he called "basic rest-activity cycles" (bracs) in humans, suggesting our bodies operate on a cycle of roughly 90 to 120 minutes throughout the day, not just during sleep. this is our ultradian rhythm.

this isn't just about sleep cycles, where we move through different stages including rem. kleitman proposed that these rhythms extend to our waking hours too, influencing our energy levels, alertness, and ability to focus. think of it as a natural ebb and flow of cognitive power, a little internal tide chart for your brain.

the 90-minute cycle: what does it mean for focus?

if kleitman's theory holds true for waking states, it suggests we have natural peaks of high alertness and focus, followed by periods of lower energy and a need for rest. for many people, these peaks seem to last around 60 to 90 minutes. during these times, you might find yourself in a state of optimal concentration.

after this peak, your brain might naturally start to signal for a break. you might feel a mental fatigue creeping in, a sudden urge to check social media, or find your mind wandering more easily. trying to push through this natural dip can often lead to diminishing returns, frustration, and burnout. it's like trying to run on fumes when the gas light has been on for twenty miles.

is it science, or just good vibes?

now, it's important to be honest here. while nathaniel kleitman's foundational work on sleep cycles and basic rest-activity cycles (bracs) is well-established, the direct, hard scientific proof applying ultradian rhythms to precisely 90-minute waking productivity blocks isn't as rigorously defined as, say, the existence of gravity. much of the evidence for this specific application is more anecdotal and based on personal experience. it's less about a definitive clinical trial proving a 90-minute peak for everyone, and more about observing patterns in human performance.

however, that doesn't mean it's not a useful framework. many people, including those who advocate for "deep work" like cal newport, have found significant personal success by structuring their most demanding tasks into longer, uninterrupted blocks. it aligns with the idea that our brains aren't just an on/off switch, but rather experience waves of varying intensity and focus capacity throughout the day. sometimes, figuring out what genuinely works for your brain, even if it's based on anecdotal but plausible observation, beats waiting for a meta-analysis.

how to actually use 90-minute blocks

the key to leveraging ultradian rhythms isn't to set a rigid 90-minute timer and never deviate. instead, it's about becoming more attuned to your own body's signals and energy levels. start by planning your most demanding, high-focus tasks for what you anticipate will be your peak energy periods. this might be first thing in the morning, or perhaps after lunch.

try committing to an extended, uninterrupted work period, aiming for anywhere between 60 to 90 minutes. during this time, silence notifications, close irrelevant tabs, and dive deep into one significant task. when you feel your focus start to wane, or your mind begins to wander, that's your signal to take a real, restorative break. this could be anywhere from 15 to 30 minutes. step away from your screen, move your body, grab a snack, or simply let your mind rest without input. then, if you're feeling refreshed, you can consider starting another cycle.

adjusting for ADHD brains

for people with ADHD, the idea of an innate, predictable rhythm might sound a bit optimistic, perhaps even a little daunting. ADHD brains often have their own unique timing, sometimes characterized by intense hyperfocus that can last for hours beyond any "rhythm", or significant challenges with task initiation and sustained attention that make even 25 minutes feel like a stretch. the "90-minute" mark might feel like an arbitrary number when your brain feels like it's running on its own wild drum solo.

the ultradian rhythm framework isn't about forcing your ADHD brain into a rigid mold. it's about observing your brain's natural patterns and tendencies. do you notice periods where you naturally get into a groove for longer, perhaps for 75 minutes or even two hours? or do you find yourself needing to reset more frequently than 25 minutes allows, but less frequently than 10 minutes? use the 90-minute idea as a flexible guideline, a hypothesis to test, rather than a hard rule. if you find yourself deeply focused past 90 minutes, don't interrupt that flow. conversely, if you hit a wall at 45 minutes, honor that signal and take the break you need. the goal is self-awareness and adjustment, not adherence to a clock.

beyond the clock: listening to your focus

ultimately, whether it's 25 minutes, the 52/17 rule, or 90 minutes, the most effective focus technique is the one that works for you in that moment. the ultradian rhythm concept simply offers another lens through which to view your productivity and energy management. it encourages a more organic, less forced approach to getting things done, moving away from purely external timers and towards internal cues.

it's about building a better relationship with your own energy levels and respecting your brain's inherent need for both intense, concentrated work and truly restorative rest. sometimes the best timer is the one inside your head, telling you when to lean in, when to pull back, and when to just let your mind wander for a bit.

the 90-minute work block, inspired by ultradian rhythms, provides a flexible alternative to more rigid productivity methods. by paying attention to your body's natural energy cycles, you can schedule your deep work more effectively and honor your need for proper rest.

if you're curious to find out which focus techniques might click with your unique brain, try the focus quiz.