Before dawn, water polo players, triathletes, and swimmers splash into chilly pools for their morning workout. Amateur runners often extend their noon lunch hour to sweat out a full weekday training session. School-age athletes typically practice between the final bell and their dinner time. Meanwhile, competitions for spectator sports—such as basketball games, baseball games, and football games—are frequently scheduled in prime-time slots beginning as late as 8 pm. Within this broad range, is there a particular time of day that’s optimal for training and performance?
Given the current interest in the individualization of training—including the collection of genetic information and screening for other measures such as blood and the microbiome—one aspect that is under-discussed is that of chronotype, and it’s closely-related cousin, the biological circadian rhythm. Well established by research, chronotype can be defined as an individual’s overall predisposition towards a preference for morning-ness or evening-ness.
Chronotypes are often discussed in the real world by categorizing people as “larks” (those that prefer mornings) and “owls” (those that prefer evenings). There is an additional category, the intermediate chronotype—sometimes called “neither types”—who don’t appear to have a firm preference for mornings or evenings. Most of us may have a pretty good idea of our chronotype. For example, I naturally prefer to stay awake until around midnight and wake up at 8 am, and I tend to do my best work later on in the day. If you’re not sure about your chronotype, several online questionnaires can help you figure it out. Perhaps the most well validated is the Munich Chronotype Questionnaire (MCTQ).
Chronotypes and the Modern Work Day
Fortunately for me and my preference for evening, I’m a remote worker and can choose the work hours that best suit me—and I do. Many people aren’t so lucky. Research suggests that only 15% of people have a morning preference, with 50% having an intermediate chronotype, and 35% have an evening preference. In most of the Western world, however, the workday begins at around 9 am, meaning most people have to awake before 7 am once travel is factored in.
It’s even worse for teenagers, who undergo a circadian shift toward evening preference during this age but often have to be at school before 9 am. Such a mismatch between chronotype-circadian rhythm and required work-school hours is a recipe for disaster, which we are only now starting to understand fully.
The mismatch between chronotype and start times for work and school often causes people to get much less sleep than they require during the week, leading to chronically under-slept people who try to compensate by oversleeping on the weekends. Accumulating many of these cycles can lead to social jet lag, which is characterized by the 80% of people who use an alarm clock regularly. If sleep-wake cycles were aligned with chronotype, there would be no need for an alarm clock.
A recent study reported that almost 70% of people experience at least an hour of social jet lag, with a third reporting two hours. Social jet lag has been linked to a number of health issues, including obesity and depression, and represents an important issue for further research.
Sleep Patterns and Performance
But what effect can all of this have on performance? A 2015 study published in Current Biology attempted to find out by recruiting 121 competitive athletes to undertake a chronotype test. There was a fairly equal mix between morning and evening preference chronotypes (approximately 25% each) while about 50% were intermediate chronotypes. The authors took a subgroup of twenty of these athletes to undertake an aerobic fitness test (the Beep test) on six different occasions: 7 am, 10 am, 1 pm, 4 pm, 7 pm, and 10 pm.
As you might expect, early chronotypes performed their best in the early trials, intermediate chronotypes in the middle trials, and late chronotypes in the later trials. The evidence supports the idea that chronotype may affect training performance at different times of day and that there’s an optimum time for different chronotypes to undertake training.
The researchers took this one step further, exploring the impact of time since waking on performance by chronotype, and again there were differences among the groups. The early and intermediate chronotypes performed best six hours after waking while the evening chronotypes performed best just over eleven hours after waking.
The results are food for thought. Most professional sport athletes train in the morning or afternoon and very rarely in the evening, suggesting that we might expect a greater number of morning chronotypes in a group of elite athletes. And, in general, this is what the research has found.
Of Brazilian Paralympic athletes, 71% were morning chronotypes as were over 60% of well-trained South African endurance athletes. A 2016 study of high-level Australian athletes found similar results where the vast majority were morning or intermediate chronotypes, with very few evening types. Indeed, they discovered that none of the triathletes were evening chronotypes and only 3% of cyclists were.
The conclusions from these studies seem obvious at first glance: athletes tend not to be evening chronotypes. We could take this a step further and suggest that, when it comes to talent identification, we could assess chronotype as an additional marker to add to the testing battery. This idea receives support from the fact that chronotype has a genetic component and is, at least partly, hardwired.
There are, however, a couple of wrinkles in this theory. As mentioned earlier, most elite athletes tend to train earlier in the day—very few train in the evening. Practical experience also tells me that this occurs more often in some sports. When I was at the University of Bath during my athletics career, the swimmers had finished their session just as I arrived for mine at 9 am. Similarly, many elite runners and cyclists started their training very early. This likely benefits them because their competitions tend to occur earlier in the day. Marathon races, for example, often have an early start and a morning chronotype would be ideal in this scenario, as it matches with training and competition.Do early chronotypes select morning sports or does early morning training cause a chronotype shift? asks @craig100m. Click To Tweet
But we find ourselves in a chicken and egg scenario. Which comes first? Do early chronotypes select morning sports or does early morning training cause a chronotype shift in these athletes, so when they undergo chronotype testing they exhibit a morning chronotype? A 2017 study in Chronobiology International gives us some insight. Here, the authors recruited 120 elite South African male rugby players and 117 non-exercising controls and gave all of them a chronotype questionnaire. On the whole, there were far more morning chronotype athletes in the rugby group—47% compared to 23% in the controls.
The authors, however, also undertook a genetic test for PER3, a gene linked to chronotype. There were no differences between the athletes and controls, suggesting that the prevalence of morning chronotype in the rugby players was due to learned behavior and not genetically determined. If this finding is true (of course, there is an alternative explanation that this particular gene might not impact chronotype, although the research suggests it does), it indicates:
- There’s a high prevalence of morning chronotypes in elite sport because the athletes tend to train in the morning, shifting their chronotype to match the time of regular training activity.
- Using a chronotype screen as a talent identification tool would be meaningless since the outcome is plastic and trainable.
Building New Habits
In addition to the study on rugby players, a 2015 study published in the European Journal of Applied Physiology put 26 swimmers through a pair of 200m swim time trials, one at 6:30 am and the other at 6:30 pm in a randomized order. On average, the morning chronotypes performed better in the morning trial, and the evening chronotypes performed better in the evening trial.
But there was also an association for habitual training time and performance. Those athletes who regularly trained in the morning tended to perform better in the morning, and those who trained in the evening clocked their best performance at that time. This finding adds further support to the idea that regular training time either has the potential to overcome chronotype preference or indeed trains it to match the new daily cycle, although this isn’t always reported.
So where does all of this leave us? When it comes to picking the best time of day for training, the morning might be best for morning chronotypes while later in the day may be ideal for other chronotypes. We also might expect that the enhanced training performance from matching training times would lead to enhanced training adaptations. To my knowledge, this hasn’t been tested.
Another consideration is whether the habitual training time matches the competition time. I’ve presented some evidence suggesting the time of day an athlete regularly trains has the potential to either shift their chronotype or reduce its impact. In athletics, most high-level competitions, such as Grand Prix events, World Championships, and the Olympic Games, are often held in the evening or have their finals in the evening. Accordingly, we could suggest athletes train at the time of day at which they compete.
There’s a caveat to this concept, though. Training in the morning means the athlete can’t have anything happen before the session that would negatively impact training quality, and morning training frees up the latter part of the day so they can contend with other tasks. Training in the late afternoon or evening, however, has the potential to disrupt events earlier in the day as well as the athlete’s social life (which, believe it or not, they do have).
Given these complications, perhaps the best solution is a compromise. An athlete should train at the time of day that best suits them regarding chronotype, availability of coach and facilities, and lifestyle. As they approach a competition, they could carry out some training at the time of day the competition will occur. This allows some circadian retraining, which could positively enhance performance. An example of this might be an athlete who often trains in the morning, but, at an upcoming major championships, knows his races are in the evening.
This is something I often did in my final preparations for the World Championships and Olympic Games—switching my training to the competition time so I could get used to the temperature and conditions at that time, and start to develop an eating routine that would match my performance. Such an approach allows the athlete to adapt favorably to training and may enhance their competition performance. Regardless, understanding an athlete’s chronotype may be important when developing the optimal training program.