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Running Hot

Posted by Matt Fitzgerald Jul 21, 2008


There is a lot of talk in the media and in the commercial sphere about the desirability of "raising your metabolism".  Raising your metabolism means increasing the rate at which your body consumes energy, or "burns calories", at rest.  The more calories your body burns at rest, the more calories you can consume in food without gaining weight, or the less you have to reduce your calorie intake to lose weight. 



The concept of raising metabolism is especially appealing to overweight men and women who do not wish to exercise.  Their thought process goes like this: "If I can just raise my metabolism enough, I can have the body of my dreams without exercising at all!"  Ironically, though, exercise itself is the single best way to elevate the body's resting metabolism.  Triathletes are likely to see great justice in this cold, hard reality.  We earn our burn.  Why should couch potatoes get it for free?



As endurance athletes, we are motivated to swim, bike and run primarily by our enjoyment of these activities and our desire to achieve personal goals, and only secondarily by vanity.  A secondary motivation is still a motivation, however, and what's more, a lean body composition is good for both appearance and performance.  So it's natural for endurance athletes to want to know how they can optimize their training and diet to raise their metabolism and get leaner.  Keep reading: your curiosity will soon be satisfied.



A Whole New EPOC



Back in the 1920s the legendary British exercise physiologist A. V. Hill first observed that the body's rate of oxygen consumption remains elevated for some time after exercise, and that this phenomenon is indicative of a metabolic rate that, while lower than the metabolic rate during exercise itself, remains above the normal resting metabolic rate.  This phenomenon has come to be known as excess post-exercise oxygen consumption (EPOC).  More recent research has determined that EPOC has two phases-a strong acute phase lasting up to two hours and a weaker long-term phase last 24 hours or more-the sum of which accounts for 6 to 15 percent of the total caloric cost of a workout, depending on its duration and intensity.  Thus, if you burn 1,000 calories during a workout you can expect to burn roughly an extra 100 calories in excess of your normal resting metabolism in the hours after the workout.



Different types of workouts produce different levels of EPOC.  High-intensity cardiovascular exercise (think interval sessions) result in the largest amounts of post-exercise energy consumption.  Indeed, EPOC increases exponentially at exercise intensities exceeding roughly 60 percent of VO2max.  Exercise scientists who performed the earliest studies on the effects of high-intensity intermittent exercise on body weight and composition were shocked by the results.  A recent study from the University of New South Wales, Australia, found that women lost an average of 10.5 percent of their fat mass after 15 weeks on a three-times-a-week program of 20-minute workouts consisting of 8-second stationary bike sprints followed by 12-second passive recoveries.  (Sounds easy but that's 60 all-out sprints-a hellishly hard workout.)  Subjects in a control group that performed traditional endurance workouts lost considerably less fat over the same period despite spending roughly 400 percent more time pedaling. 



Gym exercisers have pounced on results such as these (and other results showing that high-intensity intervals boost aerobic and anaerobic capacity in a far more time-efficient manner than conventional endurance training) to argue that high-intensity intervals are simply "better" than conventional endurance training and to imply that endurance athletes are fools for doing so much steady-state work.  However, workout duration has a big effect on EPOC, as well, and most triathletes routinely ride and run longer than the 40 minutes that the controls in the study cited above rode at the peak of their training-not to mention, we seldom ride and run as slowly as the 60 percent of VO2max at which they rode.  A study conducted by researchers at the University of New Hampshire found that a one-hour workout at 70 percent of VO2max resulted in 55 percent more EPOC than a 40-minute workout at the same intensity (which itself produced only 14 percent more EPOC than a 20-minute workout at the same intensity).



And let's not forget that 85 to 94 percent of the total energy cost of each workout comes during the workout itself, not through EPOC, and it's possible to burn a lot more calories in an exhaustive moderate-intensity workout-due to its far greater duration-than in an exhaustive maximum-intensity interval workout.  In a recent review of the scientific literature on EPOC and body weight management, researchers from University of South Australia concluded that "the earlier research optimism regarding an important role for ... EPOC in weight loss is generally unfounded... The role of exercise in the maintenance of body mass is therefore predominantly mediated via the cumulative effect of the energy expenditure during the actual exercise."  In other words, for the purpose of getting lean, going long trumps going fast-although doing some of both is better still.



The reason you would not want to perform maximum-intensity interval workouts exclusively for the sake of getting as lean as possible is the same as the reason you would not want to do the same for the sake of maximizing your fitness, despite the fact that maximum-intensity interval workouts boost aerobic and anaerobic capacity in a far more time-efficient manner than conventional endurance training.



Suppose we took the subjects in one of these eight-week studies comparing the effects of high-intensity interval training and steady-state aerobic training and asked them to continue doing what they were doing, and not only continue doing it, but to do more and more of it as long as they kept improving.  What would happen?



Well, those in the high-intensity interval group would be able to increase their volume of anaerobic training for a short while, but before long-indeed, probably right around the time they tried training every day-they would hit a wall, beyond which any additional increases would prove counterproductive.



Meanwhile, those in the slow-and-steady group would be able to continue increasing their slow-and-steady workload, and continue getting fitter, for a long, long time. Their total training volume would be vastly greater than that of the interval doers by the time they reached their own plateau, and their performance level would be significantly better in longer performance tests, although probably still worse in shorter ones.



Now let's suppose that each group began to replace their respective core training type with the other group's training to stimulate further improvement, again stopping when they plateaued. When all was said and done, the slow-and-steady folks would have reduced their slow-and-steady training by roughly 20 percent and added a volume of intervals equal to no more than 20 percent of the new, reduced slow-and-steady training volume. But the interval doers would have had to reduce their interval training by no less than 80 percent and added a volume of slow-and-steady training equal to perhaps 400 percent of their original interval volume. Both groups, of course, will now be training in precisely the same way: the way real-world competitive endurance athletes train, with a broad foundation of moderate-intensity "base" work and a thin layer of high-intensity training on top.



The lesson of this thought experiment is that you should not increase your reliance on interval training for the sake of boosting your resting metabolism or your fitness level unless you really aren't doing very much interval training.  Many triathletes do indeed underutilize high-intensity intervals, though.  One set of intervals per week in cycling and running and two to three in swimming are the right amounts.  If you're currently doing less interval training you will undoubtedly experience improvements in your body composition and performance by correcting this training imbalance, even if your training volume is slightly reduced in the process.



Gas-Guzzling Muscle



During exercise, the amount of oxygen you consume depends not only on the intensity of your exercise but also on the amount of muscle mass you carry.  Increased muscle metabolism is the cause of increased oxygen consumption during exercise, so the more muscle mass you have, the more oxygen you consume-hence, also, the more calories you burn at any given work rate.



Elevated muscle metabolism is also the cause of EPOC.  Consequently, the more muscle mass you carry, the more EPOC you will enjoy after workouts.  It's another example of the tendency for the fit to get fitter and the fat to get fatter.  Training increases the percentage of the body's mass that consists of muscle.  This change itself increases the amount of EPOC one experiences after a workout.  In other words, lean individuals get a greater post-exercise fat-burning effect than fatter individuals get from the same workout.



This was shown in a recent study involving 250 Japanese male athletes between 16 and 21 years old. Researchers measured the EPOC of each athlete for 40 minutes after short-duration exhaustive exercise. These values were compared against measurements of body size and composition.  The researchers found that differences in fat-free body mass (which is mainly muscle) accounted for 55 percent of the individual differences in EPOC. 



The lesson of this study is that, with respect to maximizing EPOC, it is best to be large and lean.  Indeed, resting metabolism in general is highest in the most muscle-bound men and women.  Of course, with respect to triathlon performance, it is best to be light and lean.  Therefore I do not recommend that you replace half of your swimming, cycling and running with heavy weightlifting for the sake of maximizing EPOC! 



That said, many age-group endurance athletes could use a little more muscle than they have.  Incorporating some maximum-intensity sprints into your training will increase your power by conditioning your seldom-used fast-twitch muscle fibers.  In addition, incorporating a small amount of strength training into your weekly regimen will further enhance your sport-specific power and reduce your injury risk by improving the stability of your joints.  A slight increase in muscle mass will also result from these changes.  This will increase your EPOC levels after workouts and also elevate your resting metabolism outside of EPOC, as it takes 30 to 50 food calories per day to maintain a pound of muscle.



The Protein Factor



They say you have to spend money to make money.  Similarly, your body has to burn calories to digest and absorb food calories.  Scientists refer to calories burned during digestion and absorption as dietary induced thermogenesis (DIT), because they produce body heat.  The "thermic effect" of different foods and nutrients can be estimated by recording subtle changes in body temperature after eating.  It so happens that protein has about twice the thermic effect of carbohydrates and about triple the thermic effect of fat, meaning protein calories are more likely than fat or carbohydrate calories to be transformed into body heat instead of body fat.



This was shown in a recent study conducted by researchers at the University of Arizona.  A group of young, healthy women were fed two sets of diets. The first diet was high in protein and the second was high in carbohydrate, while both were low in fat.  The thermic effect of the high-protein diet was found to be 100 percent greater than that of the high-carbohydrate diet.



Dietary induced thermogenesis accounts for only a tiny percentage of the body's daily energy expenditure, however.  You won't raise your resting metabolism significantly by switching to a high-protein diet.  But increasing your protein intake will help you preserve calorie-guzzling muscle mass during any period when you reduce your overall calorie intake for the sake of shedding excess body fat.  In one recent study, 158 obese men and women were placed on a diet that contained 500 fewer calories per day than their normal diet.  Half of the subjects consumed a whey protein supplement daily before breakfast and again before dinner.  The remaining subjects consumed a non-protein supplement of equal calories. The study period lasted 12 weeks. Body weight and anthropometric measurements were recorded every four weeks.



Members of both groups lost a significant amount of body weight. Those consuming the whey protein supplement lost slightly more weight, on average, but the difference was not statistically significant. However, members of the whey protein group lost significantly more body fat than controls (6.18 vs. 3.56 lbs) and lost significantly less muscle mass (2.35 vs. 5.3 lbs).



The problem with high-protein diets is that they may not be very well suited to support endurance performance.  Very little research on the effects of high-protein intake on endurance performance has been done, but in one short-term study, New Zealand researchers found that cycling time trial performance was significantly impaired after seven days on a high-protein diet.



The average American is already on a moderately high-protein diet.  A 10-percent protein diet is adequate to meet the needs of endurance athletes and non-athletes alike.  The average American gets 18 percent of his or her calories from protein.  So instead of increasing your protein intake, concentrate on making sure you consume some of your daily protein within an hour after completing each workout.  Research has shown that dietary protein is most efficiently used to synthesize new muscle tissue when consumed after exercise, and that over time athletes build more muscle and lose more fat when they routinely consume protein after exercise than when they do not, even if total daily protein consumption is held equal.



A Big Breakfast



Another dietary tactic that increases resting metabolism slightly is eating more of one's daily calorie allotment before noon and fewer calories after noon.  That's because dietary induced thermogenesis is higher in the morning than in the evening.  This was shown in a study published in the American Journal of Clinical Nutrition, in which volunteers were given an identical 544-calorie meal at one of three times. In subjects fed at 9 am, DIT increased by 16 percent; in those fed at 5 pm, DIT increased by 13.5 percent; and in those fed at 1 am, TEF increased by only 11 percent.  So it's clear that we burn more calories in the morning.



To take advantage of this phenomenon, do a little calorie counting and modify your typical meal menus to ensure that your breakfast has more calories than your lunch, and your lunch has more calories than your dinner.  This is precisely the opposite of how most of us eat, so be prepared for a major overhaul.  Use food labels and resources such as to get accurate calorie counts.



Supplemental Means



There are many diet supplements that purport to raise resting metabolism and burn off excess body fat.  Most of them do not work at all or have such a small effect on the metabolic rate that they're really not worth the distraction from better ways to get the job done.  Caffeine and green tea extract are on this list.  So is conjugated linoleic acid (CLA), a type of fat that is found in trace amounts in some meats and dairy foods.  It showed promise as a thermogenic fat reducer in early animal studies, but more recent human studies have failed to duplicate such results.



Don't Blame Your Genes



Men and women who struggle to control their weight often blame their genes for giving them a slow metabolism.  It is true that the metabolic rate is largely genetically determined.  However, lifestyle trumps genetic inheritance-in fact, lifestyle largely controls how your metabolism-regulating genes express themselves.  For example, Finish researchers recently compared "discordant" identical twins (one obese, one non-obese) and "concordant" identical twins (both non-obese) and found that, while both twins in the pairs with one obese member were more likely to have certain genes that slowed metabolism, these genes were significantly less active in the non-obese member of the discordant pairs, who tended to have a much higher fitness level.  Exercise switches of some of the genes that want to make you fat, making it almost as though we had not inherited these genes in the first place.



One of the best things you can do to increase your resting metabolism and achieve a lean body composition is to be an endurance athlete.  As an endurance athlete, you can further increase your resting metabolism by regularly engaging in high-intensity interval training and strength training, by consuming protein after workouts, and by eating a large breakfast, a medium-size lunch and a smallish dinner.  But leave the fat-burning supplements alone.



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