Internal Clock vs. External Clock—we’ve grown accustomed to organizing our work around the clock. Work starts at 8 a.m., lunch break is at noon, and the workday ends at 5 p.m. In shift work, start times, end times, and rest periods are defined even more precisely. The clock creates a common time frame, making work predictable and therefore indispensable for employers. But the worker, who follows this clock, also has another clock—the so-called “internal clock”—and it doesn’t work the same way for everyone.
8 o’clock is 8 o’clock—but not for everyone
On the clock, 8 o’clock is, of course, 8 o’clock for everyone, but biologically speaking, this time doesn’t necessarily mean the same thing for everyone, because people differ in the timing of their biological rhythms. This is particularly evident in the sleep-wake cycle. Some people reach certain biological phases earlier, while others reach them later.
In chronobiology, this individual temporal variation is described, among other things, by the term “chronotype.” Put simply, it refers to the individual, primarily genetically determined timing of the sleep-wake cycle throughout the day. This is different from what we observe in everyday life and is commonly referred to as the “internal clock.”
Someone who gets up at 6 a.m. every morning when the alarm goes off to arrive at work on time isn’t automatically a morning person. And someone who sleeps late—often called a “late riser”—isn’t automatically a night owl. Even someone with an early chronotype can sleep late. A person’s observable behavior and their biological timing are therefore not the same thing—something you only realize when you take a closer look. And that’s definitely worth doing when it comes to employees.
Getting used to something doesn’t automatically change your internal clock
Of course, people can get used to work schedules. They can learn to get up early, even if it’s difficult at first, and they can certainly function in the morning even if they don’t feel particularly productive at that time. In short, we can develop routines that help us do something that goes against our nature. But doesn’t that make it no less harmful?
In my talks, I like to compare this to shoe sizes. If you have a size 42 foot, you can certainly slip into a size 45 shoe and somehow walk in it. However, that shoe isn’t designed for optimal foot performance. You can get used to it, but in the long run, your foot will suffer damage, which will further reduce your performance potential.
The same applies to our biological capacity. The fact that a person can get up at 6 a.m. says little, at first glance, about whether that time aligns with their biological rhythm. And the fact that someone can get up at 6 a.m. every morning is still no proof that their body accepts—or even prefers—that time. The longer a person tries to function outside their biological rhythm, the higher the risk of harmful consequences—much like wearing the wrong shoe size. Adaptation is an emergency mechanism designed to bridge a short period of time, not a high-speed evolutionary process that leaves no lasting effects.
That’s a small but crucial difference.
Two “clocks” — one workstation
Let’s take two employees who both start work at 8 a.m. From an organizational standpoint, their situations are identical: both arrive at the same time and have the same workday ahead of them, with the same tasks to complete. Biologically, however, the two individuals may have completely different circumstances.
For some people, 8 a.m. may be relatively close to a phase in which their biological performance is already well advanced. For others, the same time may fall significantly earlier in their biological day—or even still be part of their biological night. This raises a question that has received relatively little attention so far in the organization of work:
What happens when the external work schedule and a person’s internal clock are out of sync?
This very question is the starting point for ChronoWorking. At first, it’s not even about changing working hours per se. Because before you change anything, you first need to understand what’s actually happening. And this is precisely where there’s a fundamental knowledge gap.
We know very well when people are supposed to work, how long they’re allowed to work, and when they’re legally required to take breaks. We can plan, document, and digitally manage work hours, but does that mean we also know what biological time a person is currently working in? You can ignore this, but then you have to live with the consequences—consequences that can be significant for employers.
The Biological Dimension of Working Hours
So as long as we view time exclusively as the time displayed on an external clock, organizing work seems relatively simple. But as soon as we also take into account our internal clock, the same workday takes on a second dimension—that of the biological internal clock, which is, moreover, extremely individual.
This fundamentallychanges our perspective on working hours, andthat is exactly what I consider to be the crucial first step. Because as soon as you understand that social time and biological time do not automatically coincide, new possibilities suddenly begin to open up, and you start asking questions that you hadn’t even considered before.
A participant in my first workshop, “Chronobiology in Human Resources Management,” held at an INQA event, put it very aptly back in 2003:
“It opens up a thousand windows…”
I still remember that sentence to this day. For the curious, every window is an opportunity, a new option, or simply: potential. For the fearful, every window is a risk, a potential danger, and “extra work that must be avoided.” In other words, a “That won’t work for us because …!” instead of a “How can we make it happen so that …!” Yet there’s no escaping the question that arises from this:
How important is the human body clock, really, to the way we organize our work?
Next week, we’ll discuss this question using a very timely example: the clock change—what actually happens to employees when the external clock changes but the body’s internal clock doesn’t simply adjust at the same moment? And… what does this cost employers? I’d love for you to join us and take part in the discussion.
You can find our white paper on the topic of “The Body Clock at Work,” also known as “ChronoWorking,” here.
