The Bunker Experiment is a famous study in chronobiology (the science of biological rhythms) that revealed how our bodies have an internal clock, even in the absence of external cues like sunlight or timekeeping devices.

It was first conducted in the 1960s in Germany but has been replicated many times since.

Test participants were housed in specially built bunkers and lived in total isolation from all external time cues and stimulation: no clocks, no daylight, no phones, no routines imposed.

The goal was to study the body’s natural rhythm without environmental influence.

What they found was that humans have built-in biological processes that occur naturally on a 24-hour cycle, called circadian rhythms.

Even in complete isolation, participants would fall into a consistent sleep-wake cycle (falling asleep and waking up at similar times each 24 hour cycle), proving the existence of an internal body clock. The body maintained other physiological rhythms (like body temperature and hormone cycles) in near-24-hour cycles as well.

Interestingly, they found that most humans have a natural circadian rhythm of 24.2 to 25 hours on average, not exactly 24, so participants' sleep and wake times would gradually drift later each day.

What the experiment showed was that our human biology is naturally rhythm-based, not just responsive to the outside world. Later studies also found that natural light exposure and daily routines help anchor our internal clocks.

Therefore, to be at your best, you need to understand your natural circadian in terms of when you are most energised and when you start getting tired. Everyone has a different profile - some people are early birds and are most productive early morning, while others are night owls who have their peak energy closer to midnight or even later.

You typically also have a natural energy dip about 8 hours after waking. If you work a 9-5, you probably recognise experiencing this after lunch.

Typical circadian rhythm

The typical 9-5 working rhythm was introduced in the 1800s and became mainstream in the 1920s with Henry Ford. It was designed for factory workers, who did repetitive tasks that required their bodies, not their brains.

The problem is that 9-5 working hours haven't changed much in the past 100 years.

We’re expected to operate like machines: steady output, minimal variation, constant (perceived) productivity.

This work schedule, coupled with expectations of constant productivity, are completely misaligned with how human energy actually works.

We've just seen that human energy naturally rises and falls in waves throughout the day, guided by circadian and ultradian rhythms.

Instead of honouring these natural peaks and dips, we push through fatigue with caffeine and screen time, ignoring the body’s signals to rest or reset.

The result?

Fatigue, brain fog, and a subtle but chronic disconnection from ourselves.

If, instead, you designed your workdays around your unique biology rather than the factory floor, you would not only perform better, you would feel better in general too.

The chart below shows (conceptually) the typical alertness and energy expenditure of a knowledge worker today. 

Typical and optimal energy profile a knowledge worker today

Awareness is one thing, implementation in practice is another.

Below are five practical steps to help you align your day, your habits, and your environment with the way your body actually works.

No hacks. Just biology-backed strategies for sustainable performance.

Remember that there’s no universal formula for productivity, because everyone’s energy operates differently. Some people thrive on predictable routines, while others need flexibility to do their best work. The key is learning to listen to your own rhythm.

1. Understand your energy profile

• Track your energy levels throughout the day for a week or two.

• Notice when you feel most alert, focused, creative, or tired every 24 hours, and also during the day. Use a simple 1–10 energy rating every few hours as a starting point.

• From here, notice your typical 24-hour rhythm in terms of when you prefer to go to bed, wake up, and do your best work.

• Also notice your ultradian rhythm and identify the typical periods of 90-120 minutes when you have the most energy during the day.

2. Design your peak performance day

• Use this data to start designing your daily schedule around your natural energy flows.

• Plan to do mentally demanding work during peak energy periods, and save admin or routine tasks for periods of low energy.

• Work in focused ~90-minute sprints, then take a 15-20 minute restorative break. Think of it like interval training for your brain: periods of performance followed by periods of rest.

• Aim for 2-3 deep focus sessions per day. Most people can do a maximum of 3-4 hours of true focused and creative work each day, before their energy and quality of their work start to suffer.

3. Implement

• If you're self-employed, make the changes for yourself and help your team and organization take similar action. Build awareness of energy rhythms and update your HR/people policies accordingly.

• If you're employed, talk to your boss and team about implementing these principles in practice. The changes of course need to be feasible within the organizational context, but typically more can be done than you think.

• Continue to track your energy throughout the day and adjust as needed.

• Don't chase perfection; focus on deliberate choices. There will be days or weeks where you have a different rhythm due to travel, heavy work loads, or similar. The key is to build awareness of the impact on your energy that your schedule and choices have, and to live in an intentional way each day.

And of course - nail the basics with regards to sleep, physical exercise, and nutrition, as they are the foundation for physical energy.

For those of you who are interested to go deeper, I expand on these concepts in my course The Inner Edge, which you can read more about here.

Productivity follows energy, not the clock.

True performance isn’t about squeezing more into your schedule, it’s about aligning your energy with how you’re built to function as a human being.

When you work with your natural rhythms rather than against them, you unlock a path to sustainable peak performance and a richer, more grounded quality of life.

Like this, energy management becomes highly strategic, and periods of downtime become a strategic enabler of peak performance, not a trade-off.

In a fast-moving world, your ability to manage yourself, including your focus, your energy, and your recovery, isn’t just a nice-to-have.

It’s your edge.