One of the many reasons you might exercise is to burn calories. Exercise burns calories while you’re doing it since it increases your body’s requirement for energy – but what happens when you stop? In some cases, the excess calorie burn ceases after the cool-down. However, this isn’t always the case. Certain types of exercise are associated with an afterburn effect. First, let’s look at what the afterburn is and then focus on the types of exercise that elicit this phenomenon.
The Afterburn Is a Calorie Burner Too
The afterburn is where your body continues to burn calories at a higher rate even after you’ve finished your workout. The scientific name for this effect is called “excess post-exercise oxygen consumption” or EPOC. As the name implies, with EPOC, you consume more oxygen and burn more calories after your workout is over. For each additional liter of oxygen your body uses during recovery, you incinerate approximately 5 additional calories. Good deal, huh?
Why is the calorie burn higher? Your body requires more oxygen and it uses the extra oxygen to recover from your training session. More specifically, the excess energy consumption goes toward reducing core body temperature, replacing short-term fuel stores (ATP-PC), the removal of lactate, the return of blood pH to normal, and oxygen replenishment. These are all important for returning your body to homeostasis.
Not all exercise elicits a significant afterburn. If you’re trying to lose weight, it’s helpful to know what types of workouts do, as the extra calorie burn gives you an added edge in slimming down. What factors determine the degree of afterburn or whether you get one at all?
Exercise Intensity
The biggest factor that determines afterburn is the intensity of a workout. A yoga workout or light jog doesn’t place enough stress on your body to trigger EPOC. Once you cease a low or even moderate intensity activity, the calorie burn stops as well, or shortly thereafter. That’s because low-intensity exercise doesn’t place enough stress on your body to build up lactate or incur an oxygen debt. So, your body doesn’t have to work as hard after the workout is over.
In contrast, when you do a high-intensity workout, your body is forced to use anaerobic pathways for energy since the intensity of the exercise makes oxidative pathways too slow. A point arises where you incur an oxygen deficit and lactate builds up. Once you stop exercising, your body has to compensate for that oxygen debt. Specifically, it has to clear out the lactate and restore your body’s normal temperature and pH. That takes oxygen and energy. Inside your sweat-soaked body, all systems are working harder during the recovery period. Exercise intensity also determines how long the afterburn lasts. As exercise intensity goes up, so does the length of the afterburn.
Exercise Duration
Exercise duration impacts the extent of the afterburn as well. In one study, researchers asked participants to exercise at 70% of their V02 max for either 20, 40, or 76 minutes. For the 20- minute session, the excess calories the participants burned afterward was only 55.5 calories. For the 40-minute walk, it was 73.5 calories, and 159.5 calories for the 76-minute walk. As you can see, the longest duration session burned more than twice the number of calories post-workout compared to the shortest session. So, next to intensity, duration is the most important determiner of EPOC.
What Types of Exercise?
As you might expect, high-intensity exercise, an intensity of at least 70% of V02 max, triggers a substantial afterburn. The longer the duration of the exercise the greater the afterburn. High-intensity interval training, as you might expect, is associated with a significant afterburn. That’s one reason it’s so popular. Yet, circuit training, too, can elicit an afterburn if you don’t rest between exercises and use enough resistance to make it challenging.
As mentioned, strength training using heavy resistance also forces your body to burn more calories during recovery. The key with strength training is to use a resistance that’s challenging enough to force your body to struggle a little. In one study, researchers compared lifting at 45% of 8-rep max and 85% of 8-rep max. The latter elicited a significantly greater EPOC with the same volume of training. Compound exercises that work multiple joints and muscle groups, especially in the lower body, are best.
What’s less effective at bringing on an afterburn is steady-state cardio, such as cycling at a moderate-intensity or jogging at a steady pace. In this case, the only way to turn up the volume of the afterburn is to increase the duration of your exercise session. Yes, you will get more of an afterburn if you do it for an hour as opposed to 30 minutes but you’ve also spent more time working out. The most time expedient way to elicit a strong afterburn is to do high-intensity interval training or do heavy resistance training.
How Long Does the Afterburn Last?
Studies looking at the length of the afterburn effect show varying results, likely due to differences in the methodology used to measure it. A study carried out in 2002 showed intense exercise can elevate your metabolic rate for as long as 38 hours after a workout. Other studies aren’t as optimistic. Some show the duration of the afterburn is as little as a few hours. Still, even a few hours of a higher metabolic rate add up over time.
Take-Home Points
· Not all exercise is equivalent in terms of the afterburn it elicits.
· Intensity and duration are the two prime determinants of EPOC. Of the two, the intensity is more important.
· Strength training elicits EPOC if you lift heavy enough.
· Steady-state exercise of at least a moderate intensity can lead to an afterburn but you have to do it for a longer duration.
· Think heavy weight, high-intensity, and short rest periods for maximal EPOC.
The Bottom Line
Intense workouts and workouts of long duration do bring about an afterburn but there’s conflicting information on how long the afterburn actually lasts. Still, any increase in calorie burn after a workout counts – so take advantage of it!
References:
Exercise After-Burn: Research Update. By Chantal A. Vella, Ph.D. & Len Kravitz, Ph.D.
Idea Health and Fitness Association. “Exercise After-Burn: A Research Update”
Med Sci Sports Exerc. 2002 Apr;34(4):715-22.
Eur J Appl Physiol 86: 411-417. (2002)
Medicine & Science in Sports & Exercise 33(6):932-8 · June 2001.
European Journal of Applied Physiology. August 2005, Volume 94, Issue 5, pp 500–504.
Related Articles By Cathe:
How Do You Know if You’re Working Out Hard Enough?
Related Cathe DVDs:
HiiT and Interval Workout DVDs