Intense exercise is anaerobic which means your body produces energy without oxygen. As a result, you build up an oxygen debt. Then, when you complete the intense anaerobic exercise, your body goes into aerobic mode for recovery. It is during this recovery that we have EPOC. During EPOC, here is a list of what is happening in your body:
- Re-synthesis of stored phosphocreatine
- Replacing muscle and blood oxygen stores
- Elevated heart rate and breathing, increased energy need
- Elevated body temperature, increased metabolic rate
- Elevated epinephrine & norepinephrine, increased metabolic rate
- Conversion of lactic acid to glucose (gluconeogenesis)
The application of EPOC to the real world of burning fat:
If you ask most people what is the best type of exercise for burning fat, they will say it is cardio. Years ago, when I first started working as a trainer, we were taught about the “fat burning zone”. Exercise physiology taught us that if you wanted to burn fat you should get into your “fat burning zone” by exercising at a low intensity (60-70% max heart rate) for a long time (over 30 minutes). Talk about time-inefficient, mind-numbing boredom!
While this style of training will work in the short term, it is not the best method. The problem with it is that the science it is based on asked the wrong question. The question we asked was, “What type of exercise uses the most (i.e. greatest percentage of) fat as a fuel source?” Compared to high intensity activities such as weight training or sprinting, the answer is low-intensity, steady-state cardio. The lower the intensity, the more fat you utilize. In fact, you are burning a greater percentage of fat as a fuel source sitting there reading this. (A quick look at the North American obesity stats should confirm to all that sitting is not an effective fat-burning exercise). However, percentage of fat utilization is not the question we should be asking. The real question is, “What can I do during the limited time I have for exercise to maximize my 24 hour caloric expenditure?” If in 24hrs I burn more calories than I consume, I lose fat.
Think back for a moment to the 20-30 meter sprint illustration. What would happen if you walked that distance? Only those in very poor shape would be out of breath during and after the 20-30 meter walk. Low intensity cardio does not result in as much EPOC. As a result, your caloric burn is largely limited to the duration of the activity. This means, you better have a lot of time on your hands if you want to burn fat!
The secret to maximizing your fat burning efforts is to exercise as hard as you safely can. (Note: get checked out by your doctor before you start exercise. Also, start slow and easy and gradually build up the intensity). The higher the intensity, the more EPOC you get. For those with sufficient strength and technical proficiency, weight training and high-intensity interval cardio are excellent choices for fat loss. Short, intense training means you get in, get it done and then enjoy being in the real fat-burning zone for several hours while you get on with your life!
Powers, Scott K., and Edward T. Howley. (2009). Exercise Physiology: Theory and Application to Fitness and Performance (7th ed.). Boston: McGraw Hill.