So next question is: is it better to work out in the am or pm?
I just read this yesterday in our local paper's fitness section:
Which time of day is optimal for exercise? Exercise scientists and those looking at chronobiology — how biological rhythms change in a daily cycle — nearly always give the same initial response in answering the question.
"For the general public, any time is better than no time for exercising," says Jason Blessinger, an exercise physiologist at California State University, Sacramento. "Biologically, your peak hours are usually midday.
That's because brain processes and cortisol (the hormone that regulates blood pressure and blood sugar) are at their peak awareness. Your chances of injury decrease." Michael Deschenes, a physiologist and neurobiologist at the College of William and Mary, has published considerable research on chronobiology and exercise. Deschenes' data suggest that early morning is not the best time to exercise for most people — especially those who are accustomed to running in the evening but switch after the time change.
The drawbacks, Deschenes says by phone from Virginia, "are less pronounced with moderate, aerobic-type exercise like your daily jog. The main problem is that the body's internal clock regulates core and muscle temperature to be at its lowest early in the morning."
Some chronobiologists have advised those with hypertension or cardiovascular risk factors not to exercise first thing in the morning.
Blood pressure peaks in the early morning, narrowing the arteries.
Conversely, body temperature, essential for maximum muscle efficiency, rises to its highest level around 4 p.m. Both factors point to the benefits of afternoon or early evening exercise.
Deschenes isn't so much concerned with early-morning joggers as he is with those who hit the gym for weightlifting or anaerobic sports.
"For those (sports) that involve 'explosive' muscle contractions like racquetball or basketball, it would be better if they can get some time in between crawling out of bed and starting exercising," he says.
Early-morning folks can at least take heart in knowing that a large body of research shows that the early birds are more likely to stay with their regimen than afternoon or evening exercisers.
