The Resting Metabolic Rate Debate
Jason R. Karp and Wayne L. Westcott
Strength training is one component of fitness that has seen tremendous growth in numbers of participants over the past several years. Its role in helping individuals lose and keep off weight has been a major sales tool among fitness professionals seeking to coax potential fitness facility members into joining their membership ranks, as well as a major motivator for members who so diligently work to train their muscles. So, it would be quite a disappointment for fitness professionals and consumers alike to find out that the effort to build and maintain muscle mass in hopes of increasing resting metabolic rate (RMR), which increases the amount of calories expended at rest, has been a waste. But, indeed, this is exactly what some fitness professionals today profess — that the research that shows the benefits of strength training for weight loss/maintenance is incorrect.
This debate about the effects of strength training could have serious repercussions for the fitness industry, and it is one that needs to be carefully examined before the issue causes confusion about the benefits of fitness for the current and future exercising public. Research has armed our industry with some powerful proof for why individuals need to exercise to prevent disease caused by sedentary lifestyles. If the public is led to believe that strength training won't translate into the results they seek, we will have taken one large step backward in the fight against overweight and obesity.
Clearly, what is important is the truth. Following are two well-researched arguments for and against the issue of whether strength training increases RMR, and whether that increase is sufficient enough to justify the recommendation of a regular program of strength training as a means for weight loss. It will be up to you to decide for yourself which argument is right.
POINT: Strength Training for Muscle PreservationBy Jason R. Karp, M.S.
Among fitness professionals, the often (over)-used argument is that strength training will add muscle, which will increase people's resting metabolic rates and, over time, help them to lose weight because muscles are "fat-burning machines." However, each pound of fat-free weight has been calculated to use about 8 to 15 calories per day,16 a negligible amount when you consider the 3,500-calorie deficit it takes to lose just 1 pound, and much lower than what is often publicized in the fitness community. Therefore, if your 200-pound client gains 2 pounds of muscle, he will expend an extra 16 to 30 calories per day. It will take 117 to 219 days for that client to expend 1 pound's worth of calories. But, since it takes a 3,500-calorie deficit compared to the number of calories consumed to lose 1 pound, not just a 3,500-calorie expenditure, it will actually take much longer to lose 1 pound from adding 2 pounds of muscle mass.
Weight training for weight lossAlthough weight training can increase muscle mass, research does not support the use of weight training alone, or in combination with aerobic training, for enhanced weight loss,15 but, rather, for the preservation of muscle mass while trying to lose weight.5 What really matters is not how much muscle a person has, but how metabolically active that muscle is. With an increase in muscle mass and an improved metabolic capacity obtained through aerobic exercise, more fat can be expended over the long term.
While it is clear that metabolic rate is acutely elevated after a workout (referred to as excess post-exercise oxygen consumption), it is not as certain that the pre-exercise (resting) metabolic rate is raised significantly with more muscle mass, as is often claimed by fitness professionals. Since the more intense the exercise, the more and longer the post-workout metabolic rate is elevated and the more calories subsequently expended,9,14 supervising your clients' cardio workouts will likely yield better results compared to having them struggle through the workouts on their own.
Resting metabolic rate does not differ much between people, including between those who are fat and lean,3 averaging about 200 to 250 milliliters of oxygen per minute, or about 3.5 milliliters of oxygen per kilogram of body mass per minute, commonly referred to in clinical practice as 1 MET (metabolic equivalent). This equates to about 9 to 11 calories per 1 pound of body mass per day. Thus, heavier people actually have higher resting metabolic rates because they have more mass to support all day. As people lose weight (when caloric expenditure is greater than caloric intake, also referred to as negative energy balance), resting metabolic rate decreases despite the maintenance of muscle mass from weight training.7 Since no research has shown that resting metabolic rate is maintained, much less increased, when people are in negative energy balance, how can fitness professionals suggest that weight training increases resting metabolic rate resulting in weight loss?
Does training increase RMR?
While a few studies have shown that resting metabolic rate (or total daily caloric expenditure) increases in response to either an aerobic or weight-training program,4,11 many have shown that it does not2,6,7,8,12,13,17 or is only increased in men.10 It has also been shown that resting metabolic rate is not significantly different between people of different aerobic fitness levels, and is independent of training status.1 Studies reporting an increase in resting metabolic rate have often been conducted on older adults who are more likely to show increases in resting metabolic rate due to the attenuating effect of weight training on age-associated losses in muscle mass. Additionally, resting metabolic rate can be increased partially as a result of increasing caloric intake, which often accompanies the increase in caloric expenditure with exercise.
While the addition of muscle mass and the post-workout elevation in metabolism certainly help your clients use more calories over the long term, the elevated metabolism during their workouts (which is much higher than afterward) has a greater effect on their overall calorie use and subsequent weight loss. And, in workouts of equal duration, cardio uses many more calories than does weight training.
COUNTER-POINT: Strength Training for Weight LossBy Wayne L. Westcott, Ph.D.
In his book LifeFit, America's leading epidemiologist, Ralph Paffenbarger, M.D., makes the following statement regarding the effects of muscle gain and metabolic change: "Indeed, when you replace 10 pounds of fat with 10 pounds of muscle, your weight remains the same, but you can expect to expend 500 or more additional kilocalories each day at rest."3 In other words, Paffenbarger ascribes the resting metabolic requirement for 1 pound of muscle at 50 calories per day.
In her book Ultimate Fitness, author Gina Kolata quotes world-renown exercise physiologist Claude Bouchard as saying, "Skeletal muscle burns about 13 calories per kilogram of body weight over 24 hours when a person is at rest."2 In other words, Bouchard ascribes the resting metabolic requirement for 1 pound of muscle at less than 6 calories per day. He supports his opinion by saying that a man who weighs about 155 pounds has about 62 pounds of skeletal muscle, which accounts for approximately 22 percent of his resting metabolism (1,600 calories resting metabolism x 22 percent used by muscles = 352 calories used by muscles ? 62 pounds of muscle = 5.7 calories per pound by muscle per day at rest). Bouchard therefore states that, "Weight lifting has virtually no effect on resting metabolism."
Revisiting the classic researchAlthough Bouchard's mathematical calculations seem to make sense, they definitely do not line up with the classic research studies on this topic. In 1994, two well-conceived and well-conducted research studies examined the effects of strength training on muscle development and resting metabolic rate. One study was conducted by Campbell and his research associates at Tufts University,1 and the other study was conducted by Pratley and his research associates at the University of Maryland.5
At Tufts University, the subjects performed progressive resistance exercise three days a week for 12 weeks. Each training session consisted of four standard strength exercises, each of which was performed for three sets of eight to 12 repetitions. After three months of training, the subjects, on average, added 3.1 pounds of lean (muscle) weight and lost 4.0 pounds of fat weight. As a result, their resting metabolic rate increased by 6.8 percent, or approximately 105 calories per day. At face value, this finding would indicate that 1 pound of muscle uses about 35 calories per day at rest (105 calories per day ? 3 pounds of muscle = 35 calories per day per pound of muscle).
At the University of Maryland, the subjects performed progressive resistance exercise three days a week for 16 weeks. Each training session consisted of 14 standard strength exercises, most of which were performed for one set of 10 to 15 repetitions. After four months of training, the subjects, on average, added 3.5 pounds of lean (muscle) weight and lost 4.2 pounds of fat weight. As a result, their resting metabolic rate increased by 7.7 percent, or approximately 120 calories per day. At face value, this finding would indicate that 1 pound of muscle uses about 34 calories per day at rest (120 calories per day ? 3.5 pounds of muscle = 34 calories per day per pound of muscle).
It is interesting to note that, in both of these studies, the same strength-training program that increased lean (muscle) weight by about 3 pounds, likewise increased resting metabolic rate by about 7 percent. It is also interesting to note that, in both of these studies, the strength-training programs responsible for these impressive results were relatively basic and brief. The Tufts University subjects performed just 12 sets of exercise per session (three sets of four exercises), and the University of Maryland subjects completed 17 sets of exercise per session (one set of 11 exercises and two sets of three exercises). These represent essentially 30-minute workouts that are manageable both time-wise and energy-wise for most adults. It is nothing short of remarkable that such modest investments in strength exercise can produce such profound physical outcomes.
Although a few studies on this topic have not noted increases in muscle mass and resting metabolic rate as a result of strength training, these have involved relatively large reductions in caloric intake. When calories are significantly restricted, the body assumes a starvation/survival mode, and does not respond in the same manner as when the appropriate amount of calories are consumed. Essentially, all studies that do not involve low-calorie diets show significant increases in muscle mass and resting metabolic rate after 10 weeks or more of sensible strength training.
Added muscle vs. trained muscleAt face value, the results of these studies indicate that 1 pound of new muscle uses about 35 calories a day at rest. However, this is undoubtedly a high estimate, since it assumes that the only training-induced change is the addition of new muscle tissue, which is entirely responsible for the metabolic increase. I submit that all of the skeletal muscle affected by the strength-training program experiences an increase in protein turnover. In other words, I suggest that all of the trained muscle tissue has a higher resting metabolic rate than it had prior to the exercise program. Of course, I can't state how many additional calories each pound of trained skeletal muscle uses, but it may be on the order of 1.5 calories per pound of muscle tissue. Let's go back to Bouchard's example and do some calculations to see if this makes sense.
If a 155-pound man with a resting metabolic rate of 1,600 calories per day has approximately 62 pounds of skeletal muscle, and each pound uses 5.7 calories per day at rest, then the contribution to his resting metabolism is about 353 calories (62 pounds of muscle x 5.7 calories per pound = 353 calories). However, if the strength-training program adds 3 pounds of muscle tissue for a total of 65 pounds of skeletal muscle, and if each pound of trained muscle now uses 7.2 calories per day at rest (a 1.5 calorie increase), then the new contribution to his resting metabolism is about 468 calories (65 pounds of muscle x 7.2 calories per pound = 468 calories). This represents about 115 additional calories expended each day at rest (353 calories to 468 calories = 115 calories), which increases his resting metabolic rate by approximately 7 percent (1,600 calories per day x 7 percent = 112 more calories). This metabolic increase is consistent with the research findings by both Campbell, et al., and Pratley, et al.
I am, therefore, suggesting that a standard three-month strength-training program may produce the following effects in previously sedentary adults:
Summary of Classic Studies on
|Campbell, et al.
|12 weeks||+3.1 lbs.||+6.8%|
|Pratley, et al.
1 set/2 sets;
|16 weeks||+3.5 lbs.||+7.7%|
1. Increase lean (muscle) weight by about 3 pounds.
2. Increase daily resting metabolic rate in all of the trained muscle by about 1.5 calories per pound (from 5.7 calories per pound to 7.2 calories per pound).
3. Increase overall resting metabolism by about 7 percent.
It makes sense that muscle tissue subjected to regular strength training has a higher metabolic rate than untrained muscle tissue. Our research indicates that regular strength training elicits an increased rate of muscle protein synthesis,4 which should elevate tissue energy usage throughout the day. In other words, strength exercise appears to have an elevating effect on muscle tissue metabolism (e.g., 1.5 calories per pound of muscle per day), and this relatively small increase multiplied by all of the trained skeletal muscle leads to a significantly higher resting metabolic rate. This explanation appears to be more reasonable than assuming that new muscle tissue uses 35 calories per pound per day, or that trained skeletal muscle still uses only 5.7 calories per pound per day.
Strength training increases RMRBased on the classic research studies conducted at Tufts University and the University of Maryland, standard programs of progressive resistance exercise can increase lean (muscle) weight by 3.0 to 3.5 pounds and resting metabolic rate by 6.8 to 7.7 percent after three to four months of regular training, respectively. It is postulated that the increased resting metabolism results from a small increase in energy usage by all of the strength-trained skeletal muscle. If this is an accurate assumption, strength-trained muscle may use approximately 1.5 more calories per pound per day than untrained muscle (7.2 vs 5.7 calories per pound per day). Such an adaptation could account for the approximately 7 to 8 percent elevation in resting metabolism observed in the reported research studies.
Strength training does have a significant elevating effect on resting metabolic rate and is, therefore, a highly beneficial exercise for increasing daily calorie usage and enhancing fat loss. It would appear that the metabolic increase occurs in all of the strength-trained muscle tissue, and that the additional energy usage may be about 1.5 calories per pound of muscle per day.
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