Ultradian rhythms: Why summer is the perfect time to rethink your energy
Your brain doesn’t run on willpower alone. Here’s how to work with your body’s natural energy rhythms…
Introduction
We all deserve to relish summer days. With most of my outdoor swimming events taking place from June until the end of September, it’s always important to me throughout this season to maximise my energy levels, to be as effective and available as possible for my clients, whilst finding time and some extra beans in the jar to enjoy my sea training.
We tend to talk about time management in hours, to-do lists, or colour-coded digital calendars. But biologically, we operate on rhythms; subtle internal cycles that shape our focus, energy, and creativity throughout the day. And while these rhythms are always there in the background, in summer, with longer days and increased light exposure, this can be an ideal time to experiment with working in a more biologically aligned way.
One lesser known but well-supported opportunity, is the ultradian rhythm; a natural cycle of approximately 90 to 120 minutes that governs not just our sleep, but our waking performance as well. Working with this rhythm, rather than ignoring it, may help counteract cognitive fatigue, improve productivity and enhance our sense of overall wellbeing.
The science of ultradian rhythms
The term ultradian simply refers to cycles that occur more than once in a 24-hour period. Many of us are familiar with the ultradian rhythm during sleep (the REM–non-REM cycle), but the same pattern may continue during waking hours. This concept was first observed by sleep researcher Nathaniel Kleitman in the mid-20th century. He called it the Basic Rest-Activity Cycle (BRAC), proposing that we move through similar waves of alertness and fatigue when we are awake.
This was later expanded by psychologist Ernest Rossi, who argued that peak performance is possible only when we honour these biological oscillations. Rossi suggested that after 90 to 120 minutes of focused mental work, the body and brain require a brief period of recovery, ideally involving rest, movement, or low-stimulation activity.
Neuroscience lends support to these claims. Functional MRI studies have shown that when we take short breaks, particularly those involving rest or being out in nature, the brain’s default mode network becomes active. This is the same network responsible for daydreaming, reflection and insight. Meanwhile, pushing through fatigue often leads to elevated cortisol and impaired executive function; a range of mental processes that are essential for decision-making and problem-solving.
Is this new?
While the roots of this research goes back several decades, what’s changed more recently is our ability to measure what’s happening in the brain during these cycles. Studies from the last ten years have used neuroimaging and hormonal tracking to show more clearly how sustained mental effort without breaks leads to reduced dopamine - a chemical that sends messages from the brain throughout the body that can impact our mood, feelings of tiredness and our ability to maintain attention. There's also a growing understanding of how these rhythms interact with light exposure, particularly in summer, when natural light can either support or disrupt our internal patterns, depending on how we engage with it.
This isn't brand-new science, but it is newly relevant, especially as more of us grapple with information overload, digital fatigue and a culture that often still confuses output with endurance.
Why summer matters
Summer is both energising and distracting. The longer days offer more light (which helps regulate cortisol and melatonin), but also more potential interruptions, whether it's social invitations, heat-induced lethargy or the general disruption of routine.
This makes it an ideal time to experiment with working in rhythm, not against it. Aligning work cycles with natural energy waves, taking a proper pause every 90 minutes or so, can help you stay focused without feeling depleted.
Something really quite simple may help: stepping outside. Research from the University of Michigan found that even brief exposure to nature, less than 10 minutes, can improve memory and attention. A meta-analysis found that as little as five minutes in a green space can significantly boost mood and self-esteem.
This doesn’t mean that a lunchtime walk will solve burnout. But it does suggest that a five-minute pause in natural light, stepping away from work to recalibrate, may have real physiological benefit. It's also one of the most simple and accessible tools we have to reclaim a little space for our busy brains during our day.
A little personalisation
The ultradian rhythm model isn’t without criticism. Some scientists point out that individual variability plays a significant role and that not everyone experiences clear-cut 90-minute energy cycle timings. Others note that most of the original work by Kleitman and Rossi was observational, and not all of it has been rigorously replicated under modern standards. But the convergence of recent data from neuroscience, cognitive psychology and environmental health makes a strong case for the principle, if not the precise timing.
In other words, you may not need a stopwatch, but you do need self-awareness.
It’s not just rest that matters; it’s fuel. If you’re finding dips in energy hard to manage, it’s worth looking at how you’re eating, too. A drop in focus mid-morning or mid-afternoon isn’t always about willpower; it can be your blood sugar, hydration, underlying health conditions, or simply not getting the right balance of nutrients to support sustained mental energy. This isn’t about strict diets or perfection, it’s about giving your brain what it needs to do its job well. When you eat in a way that supports steadiness, natural energy cycles become easier to work with, not something you’re constantly fighting.
Working with, not against
What summer offers is space; not necessarily more hours, but a subtle shift in mindset. A season that encourages fluidity. This might be the time to observe your own natural cycles. To build in short, deliberate breaks. To find your own version of the five-minute pause in the sun.
Productivity isn’t just about pushing through. Sometimes, it’s about pausing. Think about what you really need to feel better.