There is a time and place for everything. Or, indeed, if you subscribe to the theories of biorhythms, there is just a time. According to researchers studying the science of chronobiology - the relationship between our body clocks, mood and behaviour - our circadian rhythms (or 24-hour biological clocks) influence everything from muscle strength to body temperature and the best time to work out. The theory that our bodies and minds run like clockwork comes from studies that have shown how neuron signals are fired out by the hypothalamus region of the brain to control circadian rhythms. But it seems that the body's rhythms are not set in stone and can be influenced by environmental factors. This partly explains why some people swear by a 7am run to get them mentally and physically prepared for the day while others wouldn't dream of breaking a sweat before noon.
Research at the University of North Texas in Denton found that although circadian rhythms are inherent, they can be switched through habit to suit our lifestyles. It was found, for instance, that people who consistently work out in the morning taught their body to be best prepared for exercise at that time of day. When they switched to evening exercise, they didn't feel as strong. So what time of day should you exercise? Well, it all depends on what you want to achieve from your workout. Whether it's mood-boosting, strength-building or calorie-burning, there's a timetable for you.
Best time to wake up: 6-7am Dr Michael Smolensky, the director of the chronobiology centre at the University of Texas, says our internal alarm clocks are programmed to go off after seven or eight hours' sleep. With the first signs of daylight, the production of sleep-inducing hormones such as melatonin slows down. This, in turn, raises your body temperature and boosts you into action. Conversely, in the evening (10 to 11pm), the heart rate begins to slow, stress hormones plummet and a surge of sleep hormones leaves you feeling drowsy and ready for bed. By 3 to 4am, your alertness and body temperature drop to their lowest levels, a few hours before you are programmed to wake up again.
Best time to step on the scales: 7.05am Stepping on the scales as soon as you get up gives you the most accurate record of your weight, which can fluctuate by up to three pounds during the day. A study from Brown University revealed that 61 per cent of people who weighed themselves first thing maintained their weight within five pounds compared with 32 per cent who weighed in less often.
Best time to eat breakfast: 7.15-8am Between these hours, your metabolism is raring to go and your body will digest food most efficiently. Eating a healthy breakfast every day will help to stave off mid-morning cravings for fatty snacks and can help to keep weight in check, found Professor John Blundell of Leeds University. "Overnight, your body has been tapping into your fuel stores, especially carbohydrates. A high-carb breakfast optimises your morning mood and concentration and stops carbohydrate cravings later in the day," says Lyndel Costain, a dietician and the author of The Body Clock Diet.
Best time for a mood- boosting workout: 8.15am Exercise scientists at Glasgow University revealed that morning gym workouts are more effective at boosting mood. The research, which was published in the journal Appetite, looked at female subjects who took part in an hour-long aerobics class at either 8.15am or 7.15pm. Afterwards, their mood was assessed: the early-bird exercisers were shown to experience a 50 per cent boost to their feeling of well-being compared with 20 per cent for those who went to the gym in the evening. The women also said they felt that they exerted themselves more in the early classes, although the calories burnt were the same. "In the morning the exercise seemed to feel much harder, but this means the emotional benefit is much greater," says Dr Siobhan Higgins, who led the study. "People were not necessarily made happier by exercising in the morning or at night, but the change in mood was much bigger in the morning, so exercise could help set you up for a positive day." However, if you do choose a morning workout when body temperature is naturally lower, you should allow more time to warm up than you would later in the day.
Best time to do weights: lunchtime Studies have shown that strength output of muscles is at least five per cent higher at around midday; powerful anaerobic performance, such as sprinting, also improves by five per cent in the afternoon. Last year, a study in the International Journal of Sports Medicine examined peak strength at four times of the day (7-8am, 12-1pm, 5-6pm, 10.30-11.30pm) for two consecutive days. The researchers found that in the morning, values were significantly lower when compared with the rest of the day. Other studies have shown that strength is improved by as much as 4.6 per cent between morning (when it is at its lowest) and early afternoon. But why do we get stronger as the day progresses? Experts think it is linked to increases in body temperature that occur throughout the day.
Best time for main workout: 4-7pm By the mid-afternoon, body temperature is between one and two degrees warmer than in the morning, making muscles in the body more supple and lowering the risk of injury. Professor Tom Reilly, an expert in chronobiology and exercise at Liverpool John Moores University, says that most research points to late afternoon and early evening as the best times to do a gym session or main workout. In his studies, Reilly found that when people were asked to perform the same workout at different times of the day (5am, 11am, 5pm and 11pm), they felt they were working harder first thing. "Body temperature rises by a few degrees in the afternoon, warming the muscles and connective tissues, which contributes to an improvement in performance capabilities," he says. "Muscle strength is also better later in the day." Top swimmers were shown to suffer a 10 per cent drop in performance during morning training sessions. Researchers at California's San Jose University also showed that reaction times and hand-eye co-ordination, especially in sports such as tennis and football, improved after midday. Exercise in the morning and you are also more likely to catch a cold. A study in the British Journal of Sports Medicine showed that an early-morning swim left immune systems working less efficiently.
Best time to go to bed: 9.30-10.30pm A lack of sleep is known to affect both weight and fitness levels. Researchers at the sleep disorders clinic at Stanford University who recently analysed the sleep/wake patterns of sporty females found that at least eight to 10 hours of shut-eye a night was optimal to improve speed, power and general fitness. Elsewhere, scientists have found that sleep deprivation increases levels of a hunger hormone and decreases levels of a hormone that makes you feel full. The effects may lead to overeating and weight gain. The overriding message is to get to bed early.