Capriati Playing with Intensity
Excess post-exercise oxygen consumption (EPOC) is defined as the number of calories expended (above resting values) after an exercise bout, and represents the amount of oxygen the body consumes while returning to its pre-exercise state.2 This elevation in oxygen consumption equates to an elevation in calorie consumption and persists for up to 48 hours (or longer) before returning to pre-exercise states. Post exercise metabolic elevation contributes to the energy cost of exercise.3 For every liter of oxygen consumed, approximately 5 calories are required, which can add up when you are talking about trying to drop a few pounds or a few inches.2,4 The cumulative effects of EPOC over a 12 month period with regular training could produce a caloric expenditure equal to the energy stored in as much as 1.5 kilograms of adipose tissue.3 Since the cumulative effects of EPOC can add up, what type of factors can be manipulated to maximize EPOC?
The first question to answer is what types of workouts are better for increasing caloric burn? Although the impact of exercise modality has received only a little attention in the literature, it appears the answer is that all types of exercise (cardiovascular, strength, circuit and interval) will produce an EPOC effect, although at different levels. Though few studies have been done looking at resistance training and EPOC, the research available suggests that resistance training elicits a valuable EPOC response which is influenced by the intensity of the lifting. When compared to circuit training and cycling, heavy resistance training produced the greatest EPOC.2 Resistance training has been shown to increase EPOC by as much as double, especially when compounded by an increase in intensity, and can stay elevated for at least 38 hours in experienced weight lifters.3 Indeed, a higher intensity workout program has been shown to elicit a higher EPOC response than lower intensity lifting, even when the total work was kept constant. This means that you can burn the same number of calories during your workout as the next person, but if you were the one working out with intensity, your body will continue to burn more calories after your workout is done. You can actually get more results without having to do any more work than the person next to you if you work out with a higher intensity. Unlike cardiovascular training which uses oxygen consumption to measure intensity of exercise, indirect calorimetry (oxygen consumption) cannot measure the energy expenditure during non-steady-state intermittent physical activity like weight training. Because of this, intensity in resistance training is measured in volume (kilograms lifted per workout) and in percentage of one-repetition maximum.3
Both duration and intensity of exercise affect the amount of EPOC. It has been shown that duration has a direct/linear relationship with EPOC. This means that increasing exercise duration will significantly increase EPOC, although it is suggested that a 50% intensity threshold must be achieved in order for this EPOC effect to take place.2,5 When low to moderate exercise intensities were implemented (35-60% VO2 max) for 20-80 minutes, some investigators noted the EPOC duration to be less than 1 hour. Even with 2 hours of cycling at a low intensity of 30% VO2 max, 24 hour energy expenditure did not increase significantly from control day conditions.3 What this means is that yes, doing more cardio will burn more calories, but only if you put a little effort into it. Two hours of cardio with the resistance on 1 is probably not intense enough to yield much of a post workout metabolic burn.
Intensity of exercise has been shown to have the greatest impact on EPOC. Evidence suggests an exponential relationship between the magnitude of EPOC and exercise intensity for a fixed work duration.3 Even when duration was prolonged to account for an equitable total caloric burn, studies have shown that the groups with higher intensity intervals burned significantly more calories for hours after completing their workout.
Forms of higher intensity exercise that can be performed for shorter periods of time/fewer times per week have become very popular because they pose a more efficient and time effective means of inducing skeletal muscle and whole body metabolic adaptations. One approach at doing this is by incorporating high-intensity interval training (HIIT) into your workouts. HIIT employs repeated exercise intervals at high sub-maximal intensities (80-90%) 2-3 days/week. HIIT has been shown to reduce glucose utilization and increase fat oxidation. Research showed that carbohydrate oxidation dropped 16% and rate of fat oxidation and total fat oxidation was 12% higher following HIIT.6 What this means is that not only will adding high intensity intervals increase the amount of calories your body burns after your workout in the form of EPOC, it also helps ensure a greater percentage of those calories come from the energy source you want, fat. HIIT has also been shown to increase oxidative capacity and prolonged time to exhaustion in exercise at 90% of pre-trained VO2. Time to exhaustion was improved by 111% in some cases. Not only do you burn more fat calories, but you can develop greater endurance and stamina with HIIT. Individuals can “exploit the benefits of high-intensity exercise while expending the same total amount of energy as in a continuous moderate-intensity exercise bout by incorporating high intensity intervals with low-intensity recovery periods.”5 What a deal!
You are probably saying to yourself, ok, I need to increase the intensity that I work out, and I can do that by adding intervals to my routine. What other tricks do you have up your sleeve? Split training is another training technique shown to improve EPOC. An example of split-training would be performing two to four high intensity activity bouts at 75-85% intensity for 15-25 minutes separated by five minutes of active rest at a low intensity level. When compared to a continuous 50 minute run at a moderate intensity of 50%, the higher intensity work burns more calories. Another trick for elevating your EPOC is incorporating what they call supramaximal interval training. In this type of training one would perform 15-20 minutes of supramaximal activity at 105-110 % VO2 max with two to five minutes of active rest in between. Most studies have concluded that supramaximal work produces greater EPOC than submaximal training because of the additional energy expended during such high intensity training.4 One can also incorporate long, slow distance training where continuous aerobic exercise at a moderate intensity of 60-70% VO2 max is performed for 60-80 minutes to elevate their EPOC. Remember if you choose the long, slow distance method there is a linear relationship to EPOC, where as higher intensity interval work demonstrated an exponential relationship.
To summarize, if you want to elevate your calorie burn both during and after you exercise sessions, develop your training status to tolerate higher intensities of 70% of your VO2 max or 1 rep max for 30 minutes or more. Incorporate interval training into your workout, allowing you to increase total workout intensity. Also, make sure to incorporate resistance training into your routine. Not only will resistance training increase EPOC, it increases lean mass which elevates your metabolism all the time. These few strategies can allow you to burn more calories in less time, increasing your level of fitness and maximizing your results.
1. Pollock ML, Gaesser GA, Butcher JD, et al. American College of Sports Medicine Position Stand:The Recommended Quantity and Quality of Exercise for Developing and Maintianing Cardiorespiratory and Muscular Fitness, and Flexibility in Healthy Adults. Medicine & Science in Sports & Exercise. 1998;30(6):500-511.
2. Vella CA, Kravitz L. Exercise After-Burn: A Research Update. IDEA Fitness Journal. 2004;1(4). http://www.ideafit.com/fitness-library/exercise-after-burn-0.
3. Laforgia J, Withers RT, Gore CJ. Effects of exercise intensity and duration on the excess post-exercise oxygen consumption. J Sports Sci. 2006;24(12):1247-1264. http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=23093651&site=ehost-live&scope=site.
4. Dawson-Cook S. The Burn Behind the WORKOUT. American Fitness. 2009;27(3):52-54. http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=39253156&site=ehost-live&scope=site.
5. Warren A, Howden EJ, Williams AD, Fell JW, Johnson NA. Postexercise Fat Oxidation: Effect of Exercise Duration, Intensity, and Modality. International Journal of Sport Nutrition & Exercise Metabolism. 2009;19(6):607-623. http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=45453515&site=ehost-live&scope=site.
6. Perry CGR, Heigenhauser GJF, Bonen A, Spriet LL. High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle. Applied Physiology, Nutrition & Metabolism. 2008;33(6):1112-1123. http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=35731943&site=ehost-live&scope=site.
Tags: Calorie Burn, EPOC, High Intensity Interval Training, HIIT, Metabolism
