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Q. Clients often perform cardio on their own at FIT, and many of them do it at a steady-state, low-intensity level. Is this the best way to lose body fat?

A. It seems that higher intensity training consumes more calories, and that the more calories burned during the activity, the greater the fat loss, no matter what the source of these calories -- carbohydrate, fat, or protein. The overall number is the goal to losing fat mass.

But the calories burned during the activity is only a partial solution. The calories that continue to be burned after the cessation of activity is a significant factor in losing body fat. Exercises that push the body into anaerobic metabolism tend to have the greatest effect on how many calories continue to be burned after the activity. These exercises include weight training, Olympic-style weightlifting, and high-intensity interval training (such as sprinting on the treadmill, bike or Concept 2 rower). This "afterburn" is called excessive post-exercise oxygen compensation, or EPOC. This is a process that returns the body to homeostasis: clearance of lactic acid, re-oxygenation of tissues, glycogen refuel, etc. This process itself requires energy, and this energy comes from the oxidative system, where fat is the primary source.

In short, the more you can push the body into the anaerobic metabolism, the longer the EPOC. Interval training allows the individual to truly push harder than steady-state training. There is actually a lot of information on EPOC. Below is just a few of the studies out of dozens that we found in the past couple of weeks. Please check them out.

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Eur J Appl Physiol. 2002 Mar;86(5):411-7. Epub 2002 Jan 29.
Effect of an acute period of resistance exercise on excess post-exercise oxygen consumption: implications for body mass management.

Schuenke MD, Mikat RP, McBride JM.
Present address: Department of Biological Sciences, Ohio University, 128 Irvine Hall, Athens, OH 45701, USA. mschuenke@hotmail.com

Studies have shown metabolism to remain elevated for hours following resistance exercise, but none have gone beyond 16 h, nor have they followed a whole body, high intensity exercise protocol. To examine the duration of excess post-exercise oxygen consumption (EPOC) following a period of heavy resistance exercise, seven healthy men [mean (SD) age 22 (3) years, height 177 (8) cm, mass 83 (10) kg, percentage body fat 10.4 (4.2)%] engaged in a 31 min period of resistance exercise, consisting of four circuits of bench press, power cleans, and squats. Each set was performed using the subject's own predetermined ten-repetition maximum and continued until failure. Oxygen consumption ( ) measurements were obtained at consistent times (34 h pre-, 29 h pre-, 24 h pre-, 10 h pre-, 5 h pre-, immediately post-, 14 h post-, 19 h post-, 24 h post-, 38 h post-, 43 h post-, and 48 h post-exercise). Post-exercise measurements were compared to the baseline measurements made at the same time of day. The was significantly elevated ( P<0.05) above baseline values at immediately post, 14, 19, and 38 h post-exercise. Mean daily values for both post-exercise days were also significantly elevated above the mean value for the baseline day. These results suggest that EPOC duration following resistance exercise extends well beyond the previously reported duration of 16 h. The duration and magnitude of the EPOC observed in this study indicates the importance of future research to examine a possible role for high intensity resistance training in a weight management program for various populations.

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Metabolism. 1991 Aug;40(8):836-41.
Effect of intensity of exercise on excess postexercise O2 consumption.

Bahr R, Sejersted OM.
Department of Physiology, National Institute of Occupational Health, Oslo, Norway.

After exercise, there is an increase in O2 consumption termed the excess postexercise O2 consumption (EPOC). In this study, we have examined the effect of exercise intensity on the time course and magnitude of EPOC. Six healthy male subjects exercised on separate days for 80 minutes at 29%, 50%, and 75% of maximal O2 uptake (VO2max) on a cycle ergometer. O2 uptake, R value, and rectal temperature were measured while the subjects rested in bed for 14 hours postexercise, and the results were compared with those of an identical control experiment without exercise. An increase in O2 uptake lasting for 0.3 +/- 0.1 hour (29% exercise), 3.3 +/- 0.7 hour (50%) and 10.5 +/- 1.6 hour (75%) was observed. EPOC was 1.3 +/- 0.46 I(29%), 5.7 +/- 1.7 I (50%), and 30.1 +/- 6.4 I (75%). There was an exponential relationship between exercise intensity and total EPOC, both during the first 2 hours and the next 5 hours of recovery. Hence, prolonged exercise at intensities above 40% to 50% of VO2max is required in order to trigger the metabolic processes that are responsible for the prolonged EPOC component extending beyond 2 hours postexercise.

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J Appl Physiol. 1997 Jul;83(1):153-9.
Excess postexercise oxygen consumption and recovery rate in trained and untrained subjects.

Short KR, Sedlock DA.
Exercise Physiology Laboratory, Department of Health, Kinesiology, and Leisure Studies, Purdue University, West Lafayette, Indiana 47907, USA.

The purpose of this study was to determine whether aerobic fitness level would influence measurements of excess postexercise oxygen consumption (EPOC) and initial rate of recovery. Twelve trained [Tr; peak oxygen consumption (VO2 peak) = 53.3 +/- 6.4 ml . kg-1 . min-1] and ten untrained (UT; VO2 peak = 37.4 +/- 3.2 ml . kg-1 . min-1) subjects completed two 30-min cycle ergometer tests on separate days in the morning, after a 12-h fast and an abstinence from vigorous activity of 24 h. Baseline metabolic rate was established during the last 10 min of a 30-min seated preexercise rest period. Exercise workloads were manipulated so that they elicited the same relative, 70% VO2 peak (W70%), or the same absolute, 1.5 l/min oxygen uptake (VO2) (W1.5), intensity for all subjects, respectively. Recovery VO2, heart rate (HR), and respiratory exchange ratio (RER) were monitored in a seated position until baseline VO2 was reestablished. Under both exercise conditions, Tr had shorter EPOC duration (W70% = 40 +/- 15 min, W1.5 = 21 +/- 9 min) than UT (W70% = 50 +/- 14 min; W1.5 = 39 +/- 14 min), but EPOC magnitude (Tr: W70% = 3.2 +/- 1.0 liters O2, W1.5 = 1.5 +/- 0.6 liters O2; UT: W70% = 3.5 +/- 0.9 liters O2, W1.5 = 2.4 +/- 0.6 liters O2) was not different between groups. The similarity of Tr and UT EPOC accumulation in the W70% trial is attributed to the parallel decline in absolute VO2 during most of the initial recovery period. Tr subjects had faster relative decline during the fast-recovery phase, however, when a correction for their higher exercise VO2 was taken. Postexercise VO2 was lower for Tr group for nearly all of the W1.5 trial and particularly during the fast phase. Recovery HR kinetics were remarkably similar for both groups in W70%, but recovery was faster for Tr during W1.5. RER values were at or below baseline throughout much of the recovery period in both groups, with UT experiencing larger changes than Tr in both trials. These findings indicate that Tr individuals have faster regulation of postexercise metabolism when exercising at either the same relative or same absolute work rate.

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Med Sci Sports Exerc. 1989 Dec;21(6):662-6.
Effect of exercise intensity and duration on postexercise energy expenditure.

Sedlock DA, Fissinger JA, Melby CL.
Exercise Physiology Laboratory, Purdue University, West Lafayette, IN 47907.

The purpose of this study was to examine 1) the effect of two exercise intensities of equal caloric output on the magnitude (kcal) and duration of excess postexercise oxygen consumption (EPOC) and 2) the effect of exercise of equal intensity but varying duration on EPOC. Ten trained male triathletes performed three cycle ergometer exercises: high intensity-short duration (HS), low intensity-short duration (LS), and low intensity-long duration (LL). Baseline VO2 was measured for 1 h prior to each exercise condition. Postexercise VO2 was measured continuously until baseline VO2 was achieved. The duration of EPOC was similar for HS (33 +/- 10 min) and LL (28 +/- 14 min), and both were significantly longer (P less than 0.05) than the EPOC following LS (20 +/- 5 min). However, total net caloric expenditure was significantly more (P less than 0.05) for HS (29 +/- 8 kcal) than for either LS (14 +/- 6 kcal) or LL (12 +/- 7 kcal). The exercise conditions used in this study did not produce a prolonged EPOC. However, the exercise intensity was shown to affect both the magnitude and duration of EPOC, whereas the exercise duration affected only the duration of EPOC. Moreover, the duration of EPOC and the subsequent caloric expenditure were not necessarily related. Based on the resulting magnitude of the postexercise energy expenditure, it is possible that EPOC may be of some value for weight control over the long term.

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Eur J Appl Physiol Occup Physiol. 1993;67(5):420-5.
The effects of intensity of exercise on excess postexercise oxygen consumption and energy expenditure in moderately trained men and women.

Smith J, Mc Naughton L.
University of Tasmania at Launceston, Centre for Human Movement Studies, Australia.

This experiment investigated the effects of intensity of exercise on excess postexercise oxygen consumption (EPOC) in eight trained men and eight women. Three exercise intensities were employed 40%, 50%, and 70% of the predetermined maximal oxygen consumption (VO2max). All ventilation measured was undertaken with a standard, calibrated, open circuit spirometry system. No differences in the 40%, 50% and 70% VO2max trials were observed among resting levels of oxygen consumption (VO2) for either the men or the women. The men had significantly higher resting VO2 values being 0.31 (SEM 0.01) l.min-1 than did the women, 0.26 (SEM 0.01) l.min-1 (P < 0.05). The results indicated that there were highly significant EPOC for both the men and the women during the 3-h postexercise period when compared with resting levels and that these were dependent upon the exercise intensity employed. The duration of EPOC differed between the men and the women but increased with exercise intensity: for the men 40%--31.2 min; 50%--42.1 min; and 70%--47.6 min and for the women, 40%--26.9 min; 50%--35.6 min; and 70%--39.1 min. The highest EPOC, in terms of both time and energy utilised was at 70% VO2max. The regression equation for the men, where y = O2 in litres, and x = exercise intensity as a percentage of maximum was y = 0.380x + 1.9 (r2 = 0.968) and for the women is y = 0.374x - 0.857 (r2 = 0.825).

— FIT Staff