We all have our natural rhythms and cycles. None, perhaps, is more important than the circadian rhythm — the body's very own biological clock that governs, hour by hour, how alert we are feeling. On a typical workday morning, the crack of dawn can be either a welcome friend or a cruel master depending on how and when you sleep. Whether you're a morning lark or a night owl, the time you spend slumbering profoundly affects who you are and how you engage with the world while you're awake.
Your circadian rhythm is based on your body's response to a number of outside stimuli — known as zeitgebers — such as age, exercise, temperature, eating habits and, most importantly, light. The response to light is perhaps our most primeval instinct. It is, quite literally, a wakeup call to the senses and is controlled by a group of cells in the brain called the "Suprachiasmatic Nucleus" (SCN). It is the SCN that responds to light and dark signals received from the eye and which at daybreak sends signals back out to various locations (raising body temperature, for example) to bring you back to consciousness. Fundamentally, light — or lack of it — tells us when we should be awake or asleep. Once you're awake, your circadian rhythm will determine your peak moments of alertness as well as that point in the day — you know the one — when you make for the coffee cart.
It is no surprise then that a new study at the University of Birmingham in the U.K. has shown that athletes too can give quite startlingly differing performances based on the time of day they perform and, crucially, the sleep they had the night before. A paper, published in Current Biology, suggests that peak physical performance time is tied directly to the time of waking. The subjects of the study, 20 hockey and 22 squash players, were tested 6 times throughout the day – the hockey players with sprinting, the squash players with being challenged to hit a small target with the ball.
The results, say the scientists, are persuasive. Early risers, those who were used to waking between 7 a.m. and 7:30 a.m., reached their peak at midday; "intermediate risers" — getting up between 8 a.m. and 9:10 a.m. — delayed their best until around 4 p.m., whereas so-called "late risers" — those waking at 9:30 a.m. during the week and a hedonistic 11 a.m. at the weekend — were at their best at nearly 8 p.m. It may not come as a great surprise to anyone that the worst results for all three groups was at 7 a.m.
Although this was a small, initial study, the results garnered reject the common, received wisdom that there is a particular one-size-fits-all time that suits everyone. It has often been said that morning exercise results in better sleep because this is when we are most alert. Exercising when tired, the theory says, means we don't work as hard. This belief is possibly based on a misunderstanding of the sleep/wake homeostasis — the idea that the longer you are awake, the more tired you get. Although this is true, the circadian rhythm makes things a little more complex. According to the National Sleep Foundation, we experience various natural dips and peaks in our mental and physical cycle throughout the day (and night) that are not solely based on how long we've been awake. Despite this, the idea that there is an optimum workout time for everyone persists.
However, says the new study, "[c]ontrary to this view, we identified peak performance times in athletes to be different between human "larks" and "owls and that the time elapsed from waking was "the major predictor of peak performance times, rather than time of day." The paper's co-author, Dr. Roland Brandstaetter, says this is because previously athletes had been tested together regardless of their time of waking. It is only when sleep patterns are taken into account and the three groups are monitored separately, he says, that the differences are clear.
The scientists found that, depending on the time chosen to measure performance, "significant diurnal variation" could be seen in individual results. This variation could be seen most clearly in the late-rising hockey players who were asked to sprint in the morning whose abilities differed as much as "26% in the course of a day."
Though this doesn't entirely help those locked into specific work shifts — let alone international sporting events — further understanding of the effects of the body's natural cycle on physical abilities might well prove useful. Changing the habits of athletes from being late risers to early birds, for instance, could well help them with morning fixtures. And with potential increases of up to 26 percent on the table, small adjustments to sleeping patterns might well seem like a price worth paying.
Remember that age, body type, diet, health and motivation are all factors in how well you do out there when you strap on the sneakers. But, if you're not doing as well as you'd like with the fitness regime you currently have, don't be too discouraged — it's possible you're just going for that run at the wrong time. If life will allow, try altering your sleep patterns a little — it might end up doing wonders for your energy levels.