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Burning fat: during and post-exercise

What forms of exercise (continuous or interval? high-intensity or low-intensity?) are best to burn the maximum amount of fat? A recent study by Warren et al. looked at different durations and intensities of exercise to discover what type of workout gives the best long-term effect of fat oxidation- or burning fat within our bodies. The researchers compared both short and long duration cycling exercise matched with equal intensity, and two cycling exercise bouts of low and high intensity, with equal energy expenditure. The overall results: long duration and high intensity wins.

Although during long duration and short duration exercise of similar intensities you burn fat at the same rate, the double benefit of long duration is that 1.) you expend a greater amount of total calories- since your workouts are longer. In addition, with longer duration workouts 2.) you have a greater post-exercise fat utilization (oxidation). Depending on workout overload, the increased fat use can last for at least 90 minutes. Studies on resistance exercise have found increased energy expenditure levels for up to 14 hours post-workout.

While focusing on long duration exercises, you can further increase the fat burning benefits by breaking up an exercise session into several bouts.A study by Katayama et al. found that the relative contribution of fat to total energy expenditure increased when breaking up a single, 60-minute bout of exercise into two, 30-minute bouts with twenty minutes of rest in between.

When comparing high intensity vs. low intensity workouts it gets a little tricky. Although at a low intensity you are utilizing more fat than carbohydrate (in relative terms) and at a higher intensity you are using more carbohydrate than fat, post-exercise fat burning is significantly greater during the 90-minute period post-exercise following higher intensity workouts. In addition, Pillard et al. found that even if an individual eats during the post-exercise period, fat utilization will still be greater following high-intensity workouts versus low-intensity workouts. Finally, Perry et al. found that repeated higher intensity exercise elicit muscle and whole body metabolic adaptation’s that increase your body and skeletal muscle’s overall capacity to oxidize fat and carbohydrate.

The location of where you choose to exercise can also have an impact on fat utilization. Katayama et al. showed that at higher altitudes carbohydrates are utilized more, in relation to fat, and that sea-level workouts had the greatest fat utilization – however, changing altitude for fat burning is typically not a priority in determining where you live or train.

The take home message: mix up your exercise! Include weekly bouts of short duration high intensity workouts and long duration moderate intensity workouts to get the greatest fat burning benefits for your body! This type of variation is also used by top athletes to maximize training adaptations and performance – an added benefit, in addition to losing unwanted body fat, is you’ll get fitter.

- Written by Sivan Ben-David, Michael Fox and Eric Sternlicht, Ph.D. - Department of Kinesiology,        
   Occidental College, Los Angeles, CA.