Intervals & Fat Loss – Part II

February 3rd, 2008 by

Efficiency sure sounds good, but when we’re trying to lose fat, we want to be inefficient fat burners. Look at a lot of physique competitors ‚Äì they start off with 30 minutes of cardio three to four times a week and by the time they’re done dieting, they’re up to 60 minutes twice a day and even more in some cases. Did the 30 minutes four times per week stop producing results? Did they become more efficient?

But what about the often heralded fat-burning zone? I’m afraid to say that the fat-burning zone is completely overrated. Did you know that as you sit here reading this article, you are in the fat-burning zone? Do you think you’re burning lots of fat and getting ripped? The whole idea behind the fat-burning zone is that you use a greater proportion of fat as a fuel source with lower intensity work. As exercise intensity climbs, there’s a decreasing reliance on fat and an increasing reliance on stored carbohydrate in the form of glycogen to fuel activity. However, research supports the fact that the predominant fuel source used during exercise is not what is important for fat loss. Total daily energy expenditure is more important for fat loss than the major fuel used during exercise. So whether you burn fat or carbohydrate during your exercise session is not what determines your results; it’s how many calories you burned. So basically the strikes against slow cardio would be that it’s mind-numbingly boring, it’s time consuming, for a given quantity it produces less results over time, and the fat-burning zone, which is the major ‘support’ for steady state cardio, is overrated and irrelevant.

Intervals and other forms of anaerobically-intense training (weight lifting) tax the metabolic structures of the body in a way that increases overall calorie usage as well as specific use of fat for fuel over time. There have been a number of studies that have demonstrated the superiority of interval training for fat loss, despite burning fewer calories during the actual activity. In one of the landmark interval training studies, two groups were compared to one another. In this study subjects engaged in either an endurance program (4-5 times per week for 30-45 minutes) for 20 weeks or an interval training program for 15 weeks. Neither group was placed on a diet. The estimated calories burned in the endurance group was more than double that of the interval training group. However, after statistical analysis it was shown that the interval training group experienced nine times the fat loss of the endurance group. How is this possible?

While one may burn less overall calories and less fat during an interval training workout, compared to steady state cardio, when the post-exercise recovery period is factored in, interval training leads to significantly greater energy expenditure and fat loss. This is due to the effects interval training has on your metabolism. Metabolic rate is not only elevated the workout, but also for hours after the workout, and this is the magic of interval training – the fat burned in the post-workout recovery period. There are numerous other studies that support the obvious efficacy of interval training seen in the previously mentioned study. And in contrast, there are multiple studies that show that with no change in diet, the inclusion of multiple hours of slow cardio resulted in no weight loss. Think of it this way, you could drag out your trip to the gym by taking the scenic route and turning a 10-minute drive into a 45-minute drive if you really wanted to. Sure, the end result would be the same since you arrived at the gym. But you could have gotten there faster by taking a more efficient route.