If you work a 9-to-5 job and often find yourself struggling to get out of bed in the morning, or starting to flag in the late afternoon, the person to blame is Henry Ford. The founder of the Ford Motor Company started the practice in the early 1920s to keep the production lines that filled his factories churning out vehicle after vehicle as efficiently as possible.


It proved to be frighteningly effective and ushered in a new age of mass production that was copied the world over and is still referred to as Fordism today. But now, 100 years later, the 9-to-5 working week is looking more and more like it needs a serious rethink.

The rise in homeworking during the COVID pandemic has led many to question the rigidity of the working week, with many saying that the introduction of flexible hours would create a happier, more productive workforce.

This is especially true when you take into account our chronotypes – the term used to describe our natural inclination to be alert and energetic or sluggish and sleepy at a given time of day. On one end of the spectrum are owls, who naturally prefer to get up late and stay awake late, and on the other are larks, who naturally get up early and go to bed early.

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“Factors that influence chronotype are mostly genetic. We know that we wake up and go to bed at a different times. And if we look at it biologically, then we know that people have different circadian rhythms, which means that hormones, for example, are released at different times, and the body temperature changes at different times,” says Dr Anita Lenneis, a chronotype researcher based at the University of Warwick.

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One of the hormones that plays a major role in our sleep and wake cycles is melatonin.

“Melatonin is influenced by daylight, so when it gets dark, your melatonin level starts to rise and then you start to feel more tired. But it's not only dependent on light. Even if people are living in caves or if you put them in laboratories for days, then their melatonin levels still follow a circadian rhythm,” says Lenneis.

“Melatonin is maybe the best marker of circadian pace - especially dim light melatonin onset, which is the time of day when melatonin gets released in the evening. But obviously, it’s a bit intrusive sometimes and very costly to study all these biological markers.”

Most studies use a much simpler method of determining a person’s chronotype that can be followed by anyone, says Lenneis.

“We have questionnaires to find out what type you are. If you sleep on free day, you can make a calculation using the time you fall asleep, plus your sleep duration divided by two. So if you go to bed at midnight, you then sleep for eight hours, that would be four.

“If you've got a low score it means you are a very early person. And if you've got a high score, then you are a very late person. Chronotype is normally distributed, which means that only very few people are very early people, and only very few people are very late people.”

Although the concept of chronotypes has been around for a long time, exactly why our sleeping habits differ so widely still remains something of a mystery.

“There is an evolutionary idea. I don't know how true it is, but there are some people who say that when people were living in caves they had to be vigilant so needed some people to be awake all the time,” say Lenneis. “If you have some people sleeping when others are awake, then everyone is safe. You can't be eaten by a bear.”

This would obviously have been all well and good for a tribe of hunter-gatherers who were able to sleep at different times of their choosing, but clearly it’s not so great for a workforce that has to fit into a 9-to-5 pattern. And more than simply just causing sluggishness and tiredness, living to a schedule that doesn’t match our chronotype can have serious implications on our mental health, particularly for night owls.

“Basically, any kind of psychological disorder is linked to later chronotypes. We've got personality disorders, insomnia, mood disorders, anxiety disorders, substance use disorders, sleep apnoea, basically anything,” says Lenneis.

“Performance as well, especially in children. We know that children perform better in schools if they have earlier chronotypes. Your performance depends at what time you're more alert – that’s when you normally perform better. So in schools, for example, if you are very tired as an evening person then you just can't perform as well.”

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While our chronotypes do shift more towards lark than owl as we age, it is very difficult to train yourself to alter your sleep schedule.

“In one of my studies, I found that self-discipline was related to morning people and that’s something you can change. So if you normally go to bed at three, then maybe you could be more self-disciplined and try to change your schedule a bit. I think you could probably also work with light,” says Lenneis. “So maybe you turn off the light earlier then maybe you'd get tired more easily, but obviously if it's your rhythm it's going to be very difficult to change.”

Most people who attempt to live by a schedule that doesn’t match their chronotype during the week often simply end up reverting back during the weekend - a phenomenon known as social jetlag. So maybe the easy answer is to give everyone more freedom to choose their working hours.

“I think flexible working hours would help. Definitely. Because it's all about like your biological rhythm that's not aligned with your social clock. The extreme example would be in people who work shifts because their social and biological clocks do not match at all,” says Lenneis.


“Basically, if your biological clocks and your social clocks do not match, then you experience some sort of social jetlag. So it's like a mild but chronic form of jetlag. And yeah, so it basically works that if you are a late person, you go to bed at three and you still need to wake up early the next day, then you just do not get enough sleep. You accumulate sleep debt and then you need to compensate for it on weekends.”

About our expert, Dr Anita Lenneis

Anita is a researcher based at at The University of Warwick's Department of Psychology. She currently studies chronotypes.

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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.