Professional footballers are increasingly being asked to play at a variety of times - from 12.45pm kick-offs on a Saturday through to starts around 9pm on Champions League or Europa League trips to continental Europe.
Academics at the University of Birmingham have identified three broad categories or 'circadian phenotypes' - larks, intermediates and owls - by studying athletes' entrained awakening times, in other words when they usually would wake without the aid of an alarm clock or other disturbance.
Their research, which features in an article published today in Current Biology, then looked at the performance of competition-level hockey and squash players and using a variety of fitness tests found that the average owl's performance was 26 per cent worse in the early-morning tests than it was at its peak later in the day.
A 'typical' lark might wake between 6am and 7am and reach their peak five to five and a half hours after 'biological wake-up' (around midday to 1pm), an intermediate might wake between 8am and 9am and peak six to six and a half hours later, while owls might typically wake between 11am and midday and not peak for 11 hours.
Dr Roland Brandstaetter, from the University of Birmingham, said: "If a one per cent difference can be the margin between a gold medal and fourth place in the Olympic 100 metres final, just imagine what a 26 per cent boost to performance could give you. These findings remove us from the idea of 'time of day' for a race and towards the importance of the internal biological time."
Asked if the difference in performance at different times should influence team selection, Dr Brandstaetter told Press Association Sport: "Absolutely. You have matches in the afternoon, and then if you are lucky enough to get into the Champions League you start (some) matches at nine o'clock in the evening.
"So if I would want to take advantage of our circadian knowledge then what I would do as a coach is have a large enough squad, with equally skilled players in the same position but with different phenotypes, so that when I play in the Champions League I can increase the proportion of 'owls' and when I play in the afternoon or at lunchtime I increase the number of early types in my team.
"Physical performance, mental performance - and that means alertness, concentration - it all goes hand in hand."
Dr Brandstaetter says that it need not be a case of frantically buying and selling if a coach found he had a squad dominated by night owls, however.
"If you have a large proportion of owls there are possibilities to adjust their sleep/wake rhythms, to retrain their biological clocks," he added.
"We have launched a sleep clinic at the University of Birmingham to help students and staff with such issues, and we are constantly turning owls into intermediate types, so it can be done.
"What we have done is develop an intervention strategy or therapy, based on a very detailed analysis of sleep/wake rhythms. We can retrain them if they follow our advice, and it's completely non-pharmalogical."
The traditional 3pm kick-off may be on the decline, but Dr Brandstaetter says it is the best "compromise" time to play for the three distinct phenotypes.
"It's a very good time for the larks and the intermediates. It's starting to be an okay time for the owls, they're slowly getting there," he said.
"So between 3 and 5pm is probably the time you could call a compromise. From our results it would be the perfect time for the intermediates, still an okay time for the earlies - although they're declining - and also okay for the lates, because that's the time they seek increase towards their peak performance. It would be the best possible compromise."
Coaches should also bear in mind significant life events which can transform an owl into a lark.
"Being a parent creates a masking factor - it influences your biological clock because you have this factor every single day," he said.
"Your biological clock starts reading this as a daily signal, so if you have a baby that wakes up at 4am every day then your biological clock takes that as an environmental signal that it should synchronise with. And then it makes you shift to being a lark. But then of course, as the baby grows up, and this factor falls away, the parent may go back to being an owl."
:: Current Biology, Facer-Childs et al.: "The impact of circadian phenotype and time since awakening on diurnal performance in athletes" will be published online here:
