Exercise prescriptions for weight loss have long been dominated byaerobic exercise like jogging, biking, or swimming. This is despite the fact that recent and past research shows that aerobic exercise provides very little benefit over diet alone when it comes to body change. Anaerobic exercise, long ignored in discussions of weight loss, may provide unexpected benefit through previously overlooked mechanisms. Both resistance exercise using weights, and interval cardiovascular exercise that alternates periods of intense exertion with rest may provide superior benefits for weight loss with minimal investments intime.
Does Aerobic Exercise Work?
A recent study by Dr. Edward Melanson published in Exercise and Sport Science reviews April 2009 was widely reported in the media as proof against the metabolism-stimulating potential of exercise. (1) However, this study looked almost exclusively at moderate-intensity aerobic exercise like jogging, biking, or swimming. What it showed was that aerobic exercise of moderate intensity did not provide a metabolicadvantage aside from the calories burned during activity. A previousmeta-analysis done over a 25-year period came to a similar conclusion. (2) This study analyzed the data from over 400 studies comparing the effects of diet alone, aerobic exercise alone, or diet plus aerobic exercise on weight loss. The results showed that aerobic exercise did not provide a significant advantage to weight loss over diet by itself. This information is shocking, considering the pervasive belief among doctors and the exercising public that long-duration moderate-intensity aerobic exercise is a proven modality for effective weight loss.
Aerobic vs. Anaerobic exercise
While the ability of aerobic exercise to affect weight loss has been questioned, anaerobic exercise modalities like weight training andcardiovascular interval training have enjoyed increased interest. Before we go further, it is useful to briefly review anaerobic and aerobic exercise. In very simple terms, aerobic metabolism takes place inthe mitochondria and requires the use of oxygen. Anaerobic metabolism proceeds through a different pathway and requires the involvement of neither mitochondria nor oxygen. It is well known that as exercise intensity increases, anaerobic metabolism dominates; unfortunately, the exact anaerobic contribution to energy production is exceedingly difficult to measure. The standard way to approximate calorie expenditure and substrate utilization during exercise is through the measure of respiratory gases. The ratio of carbon dioxide expelled to oxygen consumed can give a predictable evaluation of not only energy use butalso fuel utilization--glucose vs. fat. However, this method is onlyvalid at lower exercise intensities. At higher intensities, the relationship is less clear.
To help address this error, researchers also measure EPOC (excess post-exercise oxygen consumption). This is a measure of the recovery energy expenditure after exercise, and it has been thought to consistof anaerobic contributions to exercise as well. There is some argument as to how meaningful this EPOC effect can be. Many researchers claim that the impact does not last long, only several hours, and amounts to at best 15% of total calories burned. However, these approximations come largely from studies with lower exercise intensities involving standard aerobic exercise protocols. Studies utilizing highly anaerobic protocols, including cardiovascular interval protocols and weight training, show a much different picture. In 2001, Schuenke et al. showed a circuit resistance training program utilizing heavy weights,short rest periods, and lasting only 31 minutes was able to generatean EPOC that persisted for 48 hours. (3) The results showed that metabolism 24 hours and 48 hours after the exercise session was increased by 21% and 19% respectively. The researchers point out that for a typical 180-pound individual, "this equates to 773 calories expended post exercise." This is far from insignificant and greatly exceeds the15% number many researchers quote for EPOC. Similar findings have been shown in women using a similar resistance-training protocol. In women, the elevation in metabolic rate lasted 16 hours. (4) The same findings have been seen with interval training as well with significantEPOC values lasting up to 24 hours. (5), (6)
Exercise Burn and 'After-Burn'
Dr. Christopher Scott of the University of Southern Maine is a pioneer in attempting to understand the full contribution of energy fromboth anaerobic metabolism and EPOC. He has published extensively in this area and is the author of one of the authoritative textbooks in this field, A Primer for Exercise and Nutritional Sciences: Thermodynamics, Bioenergetics, and Metabolism. (13) In his works, Dr. Scott points out that EPOC does not fully explain anaerobic energy use and that the anaerobic contributions to exercise may be even greater than originally thought, especially where lactic acid production is concerned. Dr. Scott emphasizes that to fully account for the calories burned during exercise, three components must be measured: calories burnedaerobically during exercise, calories burned aerobically after exercise (EPOC), and anaerobic calories burned from exercise. (7-11) EPOC and the anaerobic lactic acid measurements for exercise are considered separate by Dr Scott.
In 2005 Dr. Scott published a paper titled "Misconceptions about Aerobic and Anaerobic Energy Expenditure," where he explains his argument and highlights one of his studies comparing a 3.5-minute aerobic exercise challenge with three work-equivalent 15-second sprints. (7) When he compared the aerobic calorie use during the exercise bouts, he found the aerobic challenge burned 120KJ or 29 Kcal, while sprinting used only 16KJ or ~4 Kcal. However, when he added on the measure for EPOC, the calorie comparison for the two exercise bouts became close to equal rising to 149KJ or 36 Kcal for the aerobic bout and 165KJ or 39 Kcal for the sprint exercise. Finally, he added on the anaerobic contribution (blood lactate measure). At this point the numbers forthe anaerobic sprint exercise rose significantly. The final tally was 164KJ or 39 Kcal for the aerobic exercise compared with 273KJ or 65Kcal for the sprint exercise. By adding both EPOC and the anaerobic contribution to the original calorie total, the sprint exercise was shown to far surpass the aerobic exercise in calories burned. This is striking when one considers that the aerobic exercise session took over 4 times longer to complete (210 seconds vs. 45 seconds). What is most compelling is that without including both EPOC and anaerobic expenditure from lactate to the energy totals, a full 94% of the caloriesused during sprinting would go uncounted.
Dr. Scott has demonstrated a similar underestimation of energy usein weight training. In studies published in 2006 and 2009 in the journal of Strength and Conditioning Research, Dr. Scott quantified anaerobic energy use during weight lifting. (7), (11) Using his method ofmeasuring and quantifying all three components of calorie burn (aerobic metabolism during exercise, EPOC, and anaerobic contributions by lactate), he was able to show that weight training exercise burns 70%more calories than originally thought.
Final Thoughts
In light of this new understanding regarding exercise and weight loss, the caloric contribution for anaerobic exercise can be substantial. Given the much shorter durations of exercise required and the long exercise after-burn elicited, anaerobic exercise can make significant contributions towards creating caloric deficits for weight loss. It seems wise for health-care providers to adjust their weight loss recommendations regarding aerobic exercise to include anaerobic modalities as well. A strong anaerobic exercise program involving both weight training and cardiovascular interval training would be a wise addition to aerobically centered weight loss programs. This new understanding provides much-needed tools in the battle against obesity-related illnesses and their complications.
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