STI: What's the best time for exercise?

April 2, 2009

Fact or fiction

What's the best time for exercise?

The claim: Morning is the best time to exercise.

 

The facts: Without a doubt, exercise at any time of the day beats no exercise at all. However, are there physiological advantages to working out in the morning versus evening, or vice versa?

 

In various studies, scientists have found that subjects tend to do slightly better on measures of physical performance - including endurance, strength output, reaction time and aerobic capacity - between 4 and 7pm. The explanations are numerous: the body's temperature and hormone levels peak in late afternoon, making muscles more flexible and producing the best ratio of testosterone (the muscle-building hormone) to cortisol (the hormone that does the reverse). Stress activates cortisol secretion.

 

However, these variations have only small effects and studies have shown that the body can adapt to the time of day that you train.

 

In several long-term studies, for example, scientists randomly split people into groups and instructed them to train only in the morning or only in the early evening.

 

In the end, the morning exercisers generally did well on tests of physical performance while the evening exercisers did better when tested later in the day.

 

On a practical level, that means that if you plan to run a marathon that starts in the morning, it may be best to schedule your training runs early in the day.

 

The bottom line: In general, research suggests that the ideal time to exercise is late afternoon, though the advantages are slight.

 

The New York Times