Been trying to fit in that workout? No time like the present, right? Well, maybe not.

Seems your body may respond better to physical exertion at certain times of the day. It's all about circadian rhythm — a kind of biological clock that's generated within your body and reset almost every 24 hours.

Circadian rhythms are in almost every organism — plant or animal. There are enough researchers interested in them that they have their own journal, where you can catch up on the latest research, like the effects of altitude on circadian rhythm of adult locomotor activity in Himalayan strains of Drosophila Helvetica or theories on how central fatigue may limit endurance capacities for race horses.

May sound a tad obscure. But there could be implications for people, too.

A group of researchers wanted to find out whether there was an optimum time for elite swimmers to compete, taking into account the possibility of a circadian rhythm.

They followed a group of 25 highly trained swimmers over a 50-55 hour period and had them do half a dozen all-out 200-metre swim trials with nine hours of rest between each. They found that the swimmers did much better in the afternoon/evening than they did in the morning.

They also found that the worst time for performance was between 2:00 am and 8:00. That's a no-brainer for anyone who's ever had to drag themselves out of bed at three in the morning — for eight years — to write news for a national radio audience. But I digress.

The authors claim their study provides the first clear evidence of circadian regulation in athletic performance. They found that the circadian range from best to worst performance was 5.84 seconds. And they say it could "have considerable importance in athletic competition" — especially when you consider that a mere 1.61 seconds separated the first and eighth placed women in the 200 metre final at the 2004 Athens Olympics.

Circadian rhythms also control body temperature, which can be a key element of a more productive workout. Your body temperature is lowest when you wake up and your muscles may not be in the mood. By the afternoon, the body temp is up by as much as two degrees. Your muscles are more supple and willing. Your risk of injury could be lower.

So what's the implication for the rest of us?

Not much, I suspect. The reality of life forces most mortals to get their workout in while they can.

There are pros and cons for each. Doing it early means you've got the rest of the day for whatever else life throws at you. Research also suggests that early exercisers tend to stick to their programs more than those who leave it until later in the day.

Still, there's nothing like blowing away the stress of a long day with a brain-clearing, chest-thumping, calorie-blasting workout.

Except maybe sipping on a cool beverage on a warm beach contemplating the circadian rhythm of nothing.

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