Usain Bolt smashed the 100-metre sprint record at the 2009 World Championships in Athletics in Berlin in a floodlit stadium under an inky night sky.
This article is part of a series on fitness that answers eight questions about exercise and its influence on our bodies and minds. Read more here.
This was no coincidence: when it comes toĀ sporting prowess, timing matters. For activities relying on sheer muscle power andĀ endurance, evening or late afternoon areĀ whenĀ most world records have been set, probably due to assistance fromĀ peaks in theĀ daily rhythms ofĀ aĀ number of the bodyās key physiological outputs.
But what about everyday exercisers? Is thereĀ an optimal timeĀ of day, or month, toĀ getĀ the most out ofĀ workouts and reduce theĀ risk of injury?
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āWhichever aspect of sport you look at ā whether itās sports medicine or exercise response ā time of day matters,ā says at the University of Manchester, UK. Later afternoon or evening is when our bodyĀ temperature peaks, resulting in fasterĀ metabolic reactions and nerve signal transmission compared with the early morning. Connective tissue is also more flexible in the afternoon, while our reserves of glycogen ā the biochemical energy source our muscles draw on during moderate to intense exercise ā have had time to be replenished.
Circadian rhythms
, which could beĀ relevant for exercise: testosterone secretion peaks at around 9am; coordination tends toĀ beĀ best at around 2.30pm; reaction times areĀ fastest at around 3.30pm; cardiovascular efficiency, muscle and grip strength peak at 5Ā toĀ 5.30pm.
āCircadian rhythms exist in almost all cellsĀ of the body and regulate key processes relating to exercise and metabolism,ā says Meng. āDepending on what time you exercise, your muscle, fat and other cells will also be inĀ aĀ different state, and they will respond to exercise differently.ā
Indeed, a recent study by at Stanford University in California and her colleagues found that, on average, if they compete in theĀ evening rather than in the morning. āInĀ 40Ā per cent of [swimming] races, the time-of-day effect isĀ bigger than the difference between finishingĀ first or second,ā they wrote.
For sports involving more technical skills, such as tennis or soccer, peak performance tends to arrive a little earlier ā possibly because our cognitive abilities usually peak in the late morning or early afternoon. Soccer players at around 4pm; , but more accurate in the morning. Of course, theseĀ timings are based on averages ā in reality,Ā ālarksā who tend to wake early and beĀ more active in the mornings will be at theirĀ best earlier, while āowlsā, who naturally come to life in the evenings, will peak later.
What are the implications of all this for howĀ the rest of us time our exercise? Last year, at the University of Basel in Switzerland and her colleagues and found little to support or refute the idea that training at a specific time leads to better performance or improved health outcomes.
They did, however, find some evidence toĀ support training at the same time of day asĀ aĀ race or competition to improve physical performance at this time. In other words, morning training improves morning performance more than evening training does,Ā and vice versa. However, given that theĀ studies only included young male participants, it remains to be seen whether such conclusions apply to the general population, the authors said.
Monthly cycles
Women may have a further layer of complexity to consider. In recent years, several womenās soccer teams, including Chelsea FC Women, have started tailoring their playersā training programmes around their menstrual cycles, claiming that doing so boosts their performance and reduces their risk of injury.
āThe theory is that when oestrogen is high and progesterone is lowā¦ thatās an anabolic environment; itās a good [time] to work hard,ā says at McMaster University in Canada. Yet when he and his colleagues recently for an influenceĀ of menstrual cycle phase on exercise performance, they found it was āremarkably thinā. āThe evidence that we do have suggests that thereās no merit to it,ā says Phillips.
Even so, he doesnāt dismiss recording symptoms and using them as a guide to scheduling training. āI know some women areĀ genuinely adversely affected at certain phases of their cycle with menstrual-related symptoms: cramps, backaches, a lack of motivation, fatigue, etc. And for women athletes that do experience symptoms, tryingĀ to manage them and making their coachĀ aware of them is a great thing,ā he says.
āBut as for a blanket, āthis-is-the-way-you-do-thingsā-type approach, thereās no consistent pattern to performance when itās studied systematically, and we know gold medals andĀ world records have been set at different [menstrual] phases, and on and off the contraceptive pill.ā
Meng believes there may be yet other factors to consider. Generally, he advocates exercising in the morning ā especially outdoors ā as this exposes people to bright light, which helps to synchronise our biological clocks with the time of day. Our bodies work best when the clocks inĀ all our cells and tissues are aligned with oneĀ another, and with the time of day.
And even if there isnāt a ābestā time of dayĀ toĀ work out, there may be a time to avoidĀ exercise. Recent research by Meng andĀ his colleagues has suggested that a key mechanism for keeping the biological clocks inĀ our bones and joints synchronised with those in other tissues is exercise, and that if mice are encouraged to exercise when they would usually be sleeping, this causes their skeletal clocks to ā a phenomenon Meng has namedĀ āskeletal jet lagā.
Though the implications for injury and physical performance in humans are unclear, further experiments in mice suggest that consistently exercising during their equivalent of night-time leads to the activation of genes that are associated with osteoarthritis. āWe suspect that if you did this over a long period of time, it could be really detrimental,ā says Meng.
