You’ve probably heard of the term ‘night owls’, who stay alert until the early hours, or ‘morning larks’, who spring out of bed.
But now a study suggests there are two more patterns of shut eye, with some people being ‘afternooners’ and others ‘nappers’.
Scientists discovered that while some people’s energy levels peak in the mornings or evenings, others feel most ‘alive’ between noon and evening.
And some need a snooze between 11am and 3pm, according to a team of Russian researchers investigating sleep.
The study was led by the Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences in Moscow.
Researchers analysed six questionnaires completed by 1,305 volunteers. Most of them were women or young.
The questionnaires asked about the participants’ preferences for mornings versus evenings, as well as their body clocks and sleep quality.
They were also asked how tired they expected themselves to be at random points of the day, which varied from ‘extremely sleepy’ to ‘extremely alert’.
Based on the questionnaire results, the participants were sorted into four groups.
‘One can unmistakably recognise the division of study participants into morning, evening, and two further types,’ the researchers wrote.
While some studies suggest certain people are hyper-alert all day, this research did not find that.
It did, however, identify people as being either morning, afternoon, evening or nap-type people.
‘As many as 631 participants were identified as having either morning or evening patterns,’ the researchers wrote.
A further 550 were classed as belonging to either afternoon or napper types, the team said in the journal Personality and Individual Differences.
‘Among them 637 were assigned to only one distinct chronotype (morning or evening or afternoon or napper type),’ they added.
Some 30 per cent of the participants involved in the study failed to fit into any of the four categories.
The researchers stress, however, they relied on the participants to self report their sleep habits.
The study, led by Arcady Putilov, a researcher in sleep/wake neurobiology, was also largely made up of just one sex and age group.
He added that further research is needed to verify the four sleep groups.
It should also determine whether sleep habits are influenced by biological, genetic, psychological or environmental factors.
For instance, some night owls have been shown to fight against their natural body clocks in order to make mornings easier.
However, it is unclear if the same can be said for those who favour mornings, afternoons or naps.