If exercise is so good for you, any time is the right time, right? Maybe not. People who have an established exercise routine usually discover, through trial and error, a time of day when their workout feels easier, more invigorating, and more fun. If you exercise at different times each day and/or your workout leaves you feeling more worked over than anything else, you might want to rethink your approach.

Like every other species on the planet, we all have internal biological "clocks" that determine the circadian rhythms of our body's many systems. We all know those times of day when we're most alert or most likely to nap, those periods when it's easiest to fall asleep, think creatively; or be patient with our kids or the boss. Body temperature, sleep cycle, metabolism, and blood pressure are just a few of the biological processes regulated and "scheduled" by the hypothalamus, a gland located in the brain. Scientists have found that variations in body temperature can directly enhance or diminish exercise performance. Simply put, the higher your body temperature, the better your muscles perform, and the more productive and satisfying your workout. Warm, flexible muscles are stronger, quicker, and less likely to be injured. For most people, late afternoon is when body temperature peaks; one to three hours before you wake in the morning is when it dips the lowest (which is why warming up is especially crucial for morning exercising).

A late-afternoon workout isn't feasible for everyone, and some who try it find it makes no difference in how they feel. Even though, theoretically, the early-morning workout should be the most challenging, people who start their day with exercise may find it easier to stay committed to their program, perhaps because nothing else is competing for their attention. And they get the satisfaction of knowing they've done their exercise for the day.

A TIME TO TRAIN
No matter when you usually work out, if you're training for an upcoming event, such as the Bay to Breakers or a marathon, you will perform better if you train at the same time of day the event will be held.