|Exercise After-Burn: Research Update
By Chantal A. Vella, Ph.D. & Len Kravitz, Ph.D.
Just pick-up a recent trade magazine on the news shelf and you are sure to read about a new exercise program that will accelerate the rate at which you burn fat after completing the particular workout. For years, there have been numerous claims in the media of stepped up fat burning after particular workouts. Although enticing to the exerciser seeking optimal weight loss, rarely (if ever) is there any scientific evidence validating the particular workouts post-exercise capability to incinerate fat faster. The purpose of this article is to present a research update on the exercise after-burn and all consequential factors that influence it.
What is the Exercise After-burn or EPOC?
The exercise after-burn, or the calories expended (above resting values) after an exercise bout, is referred to as excess post-exercise oxygen consumption or EPOC. This represents the oxygen consumption above resting level that the body is utilizing to return itself to its pre-exercise state. The physiological mechanisms responsible for this increased metabolism (all chemical reactions in the body to liberate energy that is measured by oxygen consumption) include the replenishment of oxygen stores, phosphagen (ATP-PC) resynthesis, lactate removal, and the increased ventilation, blood circulation and body temperature above pre-exercise levels (Borsheim and Bahr, 2003). Studies have found that the magnitude (amount of elevation in oxygen consumption) and duration (length of time the oxygen consumption is elevated) of EPOC is dependent on the intensity and duration of exercise. It generally takes anywhere from 15 minutes to 48 hours for the body to fully recover to a resting state. Other factors influencing EPOC include training status and gender. It should be noted that several methodological differences (e.g. having subjects seated versus a recumbent position, or the techniques/criteria used to obtain resting metabolic values) in studies contribute to the wide variance in time length of EPOC.
EPOC and Cardiovascular Exercise Intensity
The intensity in an aerobic exercise bout has the greatest impact on EPOC. As exercise intensity increases, the magnitude and duration of EPOC increases. Therefore, the higher the intensity, the greater the EPOC and the greater the caloric expenditure after exercise.
Bahr and Sejersted (1991) had subjects complete exercise intensities of 29%, 50%, and 75% of VO2 max for a period of 80 minutes, and reported the greatest EPOC following the highest exercise intensity (75% VO2 max: 30.1 liters or 150.5 calories). Reader Note: Not all studies report actual caloric expenditure, but it is well understood in all exercise physiology and nutrition texts that for every liter of oxygen consumed, approximately 5 calories are burned. Additionally, following the highest intensity exercise, the duration of EPOC was significantly longer when compared to the lower intensities (10.5 hours versus 0.3 and 3.3 hours). Phelian et al. (1997) investigated the effects of low intensity (50% VO2 max) and high intensity (75% VO2 max) exercise on the EPOC response. Although the energy cost of both exercise bouts was 500 calories, the higher intensity bout caused a significantly higher EPOC than the lower intensity bout (9.0 liters, 45 calories versus 4.8 liters, 24 calories). Smith and McNaughton (1993) tested male and female subjects and reported significant increases in EPOC following the highest exercise intensity. Subjects in this study exercised at 40%, 50%, and 70% of VO2 max for 30 minutes. At the highest intensity (70% VO2 max), EPOC was 28.1 liters (140.5 calories) for men and 24.3 liters (121.5 calories) for women.
Several studies have investigated the effects of a high intensity, long duration bout of exercise on EPOC. Maehbum et al. (1986) reported an EPOC of 26 L (130 calories) following 80 minutes of cycling at 70% VO2 max in 8 men and women. They also reported that VO2 was still elevated by an average of 5% 24 hours post exercise. Similarly, Withers et al. (1991) investigated the effects of a high intensity, long duration exercise bout (treadmill at 70% VO2 max for 160 minutes) on EPOC in 8 trained males. The average EPOC value was 32.4 liters (162 calories), which is a notable contribution to overall energy expenditure. Gore and Withers (1990) reported slightly lower EPOC values following 80 minutes of running at 70% VO2 max in 9 male subjects (14.6 L, 73 calories). These studies reveal that EPOC can contribute significantly to overall caloric expenditure, but do appear to vary somewhat between subjects.
Sedlock (1992) reported a very low EPOC average of 3.1 liters (15.5 calories) following 30 minutes of cycling at 60-65% VO2 max. In a similar study (Sedlock et al, 1989) the average EPOC following 20 minutes of exercise at 75% VO2 max was only 6.2 liters (31 calories). These findings further indicate that there may be subject differences in the EPOC response following exercise.
In summary, that data clearly show that exercise intensity is the main factor in determining the magnitude and duration of EPOC following aerobic exercise. Thus, when developing a cardiorespiratory exercise prescription for weight maintenance and weight loss, the influence of exercise intensity on EPOC and its potential contribution to total caloric expenditure should be taken into consideration.
EPOC and Cardiovascular Exercise Duration
The duration of an aerobic exercise bout also affects EPOC. Research consistently reports a direct relationship between the duration of exercise and EPOC. Chad and Wenger (1988) investigated the effects of exercise duration (30, 45, and 60 minutes) at 70% VO2 max on EPOC. They reported EPOC values of 6.6 liters (33 calories over 128 minutes), 14.9 liters (74.5 calories over 204 minutes) and 33 liters (156 calories over 455 minutes) for durations of 30, 45, and 60 minutes, respectively. It was concluded that increasing exercise duration would significantly increase total EPOC. Quinn et al. (1994) had women walk on a treadmill at 70% VO2 max for 20, 40, and 60 minute durations. The authors reported a significantly higher and longer EPOC following the 60 minute duration when compared to both shorter durations. The values were 8.6 liters (43 calories), 9.8 liters (49 calories) and 15.2 liters (76 calories) for 20, 40, and 60 minute durations, respectively. In a similar study, Bahr et al (1987) had subjects exercise for 20, 40, and 76 minutes at 70% VO2 max and reported EPOC values of 11.1 liters (55.5 calories), 14.7 liters (73.5 calories) and 31.9 liters (159.5 calories) for each duration, respectively. These studies suggest that given sufficient aerobic exercise intensity, exercise duration is an important factor influencing EPOC.
Intermittent versus Single Bouts of Exercise
Several studies have concluded that intermittent aerobic exercise bouts elicit a greater EPOC response when compared to continuous exercise bouts. Laforgia et al. (1997) investigated the effects of a continuous run (30 minutes at 70% VO2 max) versus an interval run (20 bouts of 1 minute duration at 105% VO2 max referred to as supramaximal exercise). The authors reported a significantly greater EPOC following the intermittent bouts of supramaximal exercise (15 liters, 75 calories versus 6.9 liters, 34.5 calories). Kaminski et al. (1990) reported a significantly greater EPOC following an intermittent bout of exercise (two 25 minute sessions at 75% VO2 max) when compared to a continuous bout of exercise (50 minute continuous run at 75% VO2 max). The EPOC values for the split exercise sessions were combined, and averaged 3.1 liters (15.5 calories) versus 1.4 liters (7 calories) for the continuous exercise bout. Similarly, Almuraini et al. (1998) reported greater EPOC values following two, 15 minute exercise bouts when compared to 30 minutes of continuous exercise at 70% VO2 max. The average EPOC following intermittent exercise was 7.4 liters (37 calories) versus 5.3 liters (26.5 calories) following continuous exercise. Interestingly, the EPOC values from Kaminski et al. (1990) and Almuraini et al. (1998) are significantly lower than the values reported from similar studies, further supporting the hypothesis that the EPOC response may vary among individuals and the possible influence of scientific methodological techniques employed. Additionally, incorporating high intensity intervals into continuous exercise has also been found to significantly increase EPOC (Kaminski and Whaley, 1993).
Resistance Training and EPOC
Very few studies have investigated the effects of resistance training on EPOC. Research findings suggest that resistance training also elicits a valuable EPOC response for weight loss and/or weight management. Although it is difficult to equalize resistance training and aerobic exercise, Elliot et al. (1988) investigated the difference in EPOC between aerobic cycling (40 minutes at 80% heart rate max), circuit training (4 sets, 8 exercises, 15 reps at 50% 1RM) and heavy resistance training (3 sets, 8 exercises, 3-8 reps at 80-90% 1RM). Heavy resistance training produced the greatest EPOC (10.6 liters, 53 calories) compared with circuit training (10.2 liters, 51 calories) and cycling (6.7 liters, 33.5 calories). In a similar study by Gilette et al. (1994), resistance training (5 sets, 10 exercises, 8-12 reps at 70% 1RM) elicited a significantly greater EPOC response when compared to aerobic exercise (50% VO2 max for 60 minutes).
Additionally, a higher intensity resistance training program has been found to elicit a greater EPOC than a lower intensity resistance training program, when total work is kept constant. Thornton and Potteiger (2002) studied the effects of a high intensity (2 sets, 8 reps, 85% of 8RM) versus low intensity (2 sets, 15 reps, 45% 8RM) resistance training workout, keeping total work constant, on EPOC and found a significantly greater EPOC with the high intensity program (11 calories versus 5.5 calories). In a study by Murphy and Swartzkopf (1992), standard resistance training (3 sets, 6 exercises, reps to exhaustion at 80% 1RM, 120 second rest) was compared to circuit resistance training (3 circuit sets, 6 exercises, 10-12 reps at 50% 1RM, 30 second rest). Total work volume of both programs was similar, however, circuit resistance training elicited a greater EPOC response when compared to the standard resistance training program (5 liters, 25 calories versus 2.7 liters, 13.5 calories). The data on resistance training and EPOC suggest that EPOC is distinctly influenced by the intensity of the resistance training program.
The training status of an individual may also have an effect on EPOC. Studies are inconclusive but suggest that trained individuals recover from exercise faster than their untrained counterparts. One reason for the inconsistencies in the research is that it is difficult to match exercise intensity and total work performed for trained and untrained individuals. If matched relative to fitness level, the trained individual would be working at a higher intensity than the untrained individual. Several studies have reported a more rapid fall in EPOC (Short and Sedlock, 1997) and a shorter duration of EPOC in trained subjects (Frey et al., 1993). Even though people with higher fitness levels appear to have a faster recovering EPOC, due to their generally higher training intensities and duration the magnitude of their EPOC is still quite prominent.
Gender and EPOC
Gender is also a factor that may influence EPOC. Research shows that energy expenditure with women at rest and during exercise varies with the menstrual phase (Borshein and Bahr, 2003). Typically, resting energy expenditure is lowest one week before ovulation and highest during the 14-day luteal phase following ovulation, thus accordingly affecting EPOC.
Few controlled studies have been conducted to compare EPOC in men and women. Therefore the gender effect on EPOC is not fully elucidated.
Although there appears to be variation in individual responses, the positive news is that any additional caloric expenditure following exercise can add up over time and may contribute to long-term weight management. Some evidence-based exercise options to maximize the exercise after-burn are presented in Sidebar 1. When working with clients who want to maximize energy expenditure through EPOC, focus on developing their training status so they can perform higher intensity exercise for periods of 30 minutes or more. In addition, regularly incorporate interval training workouts, as this type of training positively enhances EPOC. Most of the current literature supports exercise intensities at or above 70% of VO2 max for optimal energy expenditure following exercise. Additionally, encourage clients to engage in resistance training at least 2 times a week. Not only will resistance training maintain or increase muscle mass in weight-loss interventions, studies report a meaningful EPOC effect following high intensity and circuit resistance training.
EPOC Sidebar 1
Exercise Program Suggestions to Maximize the Exercise After-burn (EPOC)
1. Tempo training: continuous, aerobic exercise at a high-intensity (70-85% VO2 max) for a period of 30-60 minutes (Smith & McNaughton, 1993).
2. Long slow distance training: continuous, aerobic exercise at a moderate intensity (60-70% VO2 max) for a period of 60-80 minutes (Withers et al., 1991).
3. Split training: 2 to 4 high-intensity exercise bouts (70-85% VO2 max) for a period of 15 to 20 minutes, separated by 5 minutes or up to 6 hours (Kaminsky et al., 1990).
4. Continuous interval training: alternate 3 min bouts of low (30-40% VO2 max) and high intensity exercise (80-90% VO2 max) for a period of 30-60 minutes (Kaminsky & Whaley, 1993)
5. Supramaximal interval training: 15-20 supramaximal exercise bouts (105-110% VO2 max) for a period of 1 minute, with 2-5 minute rest periods (Laforgia et al., 1997).
6. Heavy Resistance training: 2-4 sets, 8-10 exercises, 3-8 reps at 80-90% 1RM, 2-3 minutes rest (Elliot et al., 1992).
7. Circuit Resistance training: 2-3 circuit sets, 6-10 exercises, 10-12 reps at 50% 1RM, 30 seconds rest (Murphy & Schwarzkopf, 1992)
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