A majority of people who perform cardio do so to burn fat. The quest to optimize fat loss from cardio has made the term “fat burning zone” a buzzword in the fitness industry; so much so that “fat burning zone” programs have been integrated into almost every treadmill, elliptical trainer and stationary bike on the market. (See my previous post on the Myth of the Fat Burning Zone for a critical analysis of this strategy).
An often overlooked fat-burning aspect of cardio is its effect on excess-post exercise oxygen consumption (EPOC). Simply stated, EPOC is the number of calories you expend after the completion of a workout to return your body to its homeostatic state. It’s often referred to as the “afterburn” and includes such processes as the resynthesis of phosphagens, removal/conversion of lactate, restoration of glycogen, reoxygenation of blood, and the return of breathing and heart rate to normal levels.
Some researchers and fitness pros, however, have questioned the applicability of EPOC in promoting fat loss. A recent NY Times article quoted an exercise physiologist as saying the metabolic effects of EPOC are negligible. Others have echoed similar sentiments, claiming that the only relevant impact of cardio on fat loss is the number of calories burned during the workout. What gives?
The issue here can be summed up in a word: intensity. Namely, low intensity exercise has a minimal impact on EPOC, with an afterburn of only a few minutes. Read: If you walk for an hour, don’t expect to burn many calories once you stop walking. On the other hand, high-intensity cardio has a substantial effect on EPOC. How substantial? A recent study (1) showed that a 45 minute bout of cardio performed at approximately 73% of VO2 max increased post-exercise caloric expenditure by a whopping 190 calories! This represented an additional 37% expenditure over and above the 500+ calories burned during the workout itself. To put these results in perspective, every 2.5 weeks you’ll burn an extra pound simply from the effects of EPOC. Not too shabby, huh?
What’s the take home message? If you want to maximize fat loss from cardio, you need to up the intensity. As I’ve discussed before, high-intensity interval training is an excellent strategy to ramp up fat burning. Forget the fat burning zone. Push yourself to train above your lactate threshold, at least for portions of your exercise bout. You’ll reap fat burning rewards long after you stop exercising.
Knab AM, Shanely RA, Corbin K, Jin F, Sha W, Nieman DC. A 45-Minute Vigorous Exercise Bout Increases Metabolic Rate for 14 Hours. Med Sci Sports Exerc. 2011 Feb 8. [Epub ahead of print]