Tuesday, June 21, 2011

The Effect of Exercise Duration on Fat Loss

The length of your exercise bout is well known to have a profound effect on how much fat you burn during and after your workout.  When discussing post-working fat burning, we’re really alluding to EPOC (or excess post exercise oxygen consumption), which is number of calories your body burns to recover back to a resting state.

Research consistently reports that a direct relationship exists between the duration of exercise and EPOC. In one study, women were asked to walk on a treadmill at 70% VO2max for 20, 40 and 60 minutes. The authors reported a significantly higher and longer EPOC following the 60-minute duration treadmill workout. The values were 8.6 liters of oxygen (43 calories), 9.8 liters of oxygen (49 calories) and 15.2 liters of oxygen (76 calories) for 20-, 40- and 60-minute durations, respectively.

Another study investigated the effects on EPOC of exercise duration (30, 45 and 60 minutes) at 70% VOmax.

They reported EPOC values of 6.6 liters of oxygen (33 calories over 2 hours), 14.9 liters of oxygen (74.5 calories over 3.4 hours) and 33 liters of oxygen (165 calories over 7.6 hours) for durations of 30, 45 and 60 minutes, respectively. The researchers concluded that increasing exercise duration significantly increased total EPOC.

In a similar study, subjects exercised for 20, 40 and 80 minutes at 70% VO2max and had EPOC values of 11.1 L (55.5 calories), 14.7 L (73.5 calories) and 31.9 L (159.5 calories) for each duration, respectively.

Studies have also investigated the effects of combining high intensity exercise with even longer duration. Maehlum and colleagues reported an EPOC of 26 L (130 calories) following 80 minutes of cycling at 70% VO2max in eight men and women. In addition, the subjects’ VO2 was still elevated by an average of 5% for 24 hours post-exercise!

In studies investigating EPOC following shorter-duration exercise, the results are quite different. But do keep in mind that the following 2 studies used very moderate exercise intensities. In one of these studies, a very low EPOC average of 3.1 L (15.5 calories) was observed following 30 minutes of cycling at just 60%–65% VO2max. And, in another study, Sedlock and colleagues found that the average EPOC following 20 minutes of exercise at 75% VO2max was only 6.2 L (31 calories).

So I’m pretty sure that you can now see that an overwhelming number of studies conclude that exercise duration can heavily impact EPOC, which can contribute significantly to overall caloric expenditure. So if you want to burn than crank up the intensity of your workouts and the longer you can maintain that intensity, the better.


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