Muscle, Metabolism & More

by David Greenwalt

Dave & MaryIt used to be thought that for each new pound of skeletal muscle gained, you would burn an extra 50 calories each day.

At that rate, the thinking goes, you could put on muscle by lifting weights (or other strength training), and then let your muscles burn away calories. You could lose weight the rest of the day by just sitting still.

Too good to be true?

This article will examine the scientific evidence about how muscle and strength training really affect not only our metabolism, but also our risk of disease.

How many calories does skeletal muscle really use?

Numerous studies have shown that skeletal muscle at rest actually uses only about 5 to 7 kcal per pound per day (1, 2, 3) – a far cry from the 50 kcal/day often cited.

By this estimate, if you were to add three pounds of muscle, you would only burn about 18 extra calories per day. That would earn you about one-fifth of one banana, or not quite two Doritos (4).

Said another way, adding three pounds of muscle would only increase your Resting Metabolic Rate (RMR) – how many calories your body uses at rest – by about 18 calories.

Not very much, is it?

The truth is that only a very small proportion of the calories that our bodies need to operate every day is used by skeletal muscle.

In terms of Total Daily Energy Expenditure (TDEE) – which is essentially where our calories are ‘spent’ on maintaining body systems, digesting food, and physical activity – muscle tissue uses only about 20% of our total calories. By contrast, the heart, lungs, kidneys, brain, and liver use about 80% of TDEE. The metabolic rate of these organs is 15 to 40 times greater than that of skeletal muscle (3).

While adding muscle doesn’t increase RMR much, that definitely doesn’t mean that strength training is not important.

Strength training benefits our metabolism and overall health in many important ways, including by preventing muscle loss and decreasing risk of disease (5, 6, 7). We’ll discuss the numerous benefits of strength training later in this article.

The bottom line: Each pound of skeletal muscle at rest uses only about 5 to 7 calories per day. Our major organs – heart, kidneys, lungs, brain, and liver – use a much larger percentage of our daily calories than skeletal muscle does.

Is RMR really important anyway?

So, adding extra skeletal muscle may not be the most effective way to increase your metabolic rate. But is raising your metabolic rate really important anyway?

If increasing your RMR is your goal, the quickest way to do that is probably by gaining weight from fat, rather than muscle.

This is because our internal organs get bigger as body mass increases, and organs burn a lot more calories at rest than muscle does (3, 8).

Since it’s usually a lot easier to gain fat than it is to add muscle, adding fat is likely the quickest way to increase body mass.

Furthermore, since overweight people have more body weight to carry around, every bit of movement or exercise they do uses more calories, again increasing their calorie needs.

But what good is having a higher RMR if you are unhealthy? Being overweight or obese increases your risk of many diseases, including diabetes, heart disease, and some types of cancer (9). Is having a higher RMR really worth increasing your risk?

Having a higher RMR certainly doesn’t mean that you will lose weight more easily, especially if you’re obese. In fact, being overweight or obese throws your metabolic processes out of whack in many ways that usually make it harder to lose weight.

Remember, RMR is simply an accounting of how many calories your body requires at rest. To manage your weight, the calories required need to be matched to the calories taken in. The actual number itself is not as important as is the balance of calories in/calories out.

If the goal is to lead a healthy, quality life, just focusing on increasing your RMR is far from the best way to achieve that.

The bottom line: While people often think that increasing metabolic rate is a good idea, it is really the balance between calories taken in and calories used that matters. Being healthy overall is much more important than just attaining a high RMR.

Strength training can help with weight loss

While it doesn’t increase RMR much, building muscle does have many other benefits, including metabolic benefits for people trying to lose weight.

At first glance, it might seem like strictly focusing on calorie-burning cardio and/or cutting calories would be the best way to lose weight.

While it’s true that you usually burn more calories doing moderate- or high- intensity cardiovascular exercise than you do while strength training, the muscle built through strength training is important to your metabolism as well (10).

When you lose weight, either by doing cardiovascular exercise or dieting, you are losing fat tissue and possibly (but hopefully not) skeletal muscle tissue. Since both muscle and fat tissue use calories, having less of these tissues means that you will not require as many calories overall. Your RMR will eventually decrease to match your new size.

In addition to a lower RMR, your new smaller size means that you will also burn fewer calories doing any sort of activity, including exercising and everyday chores (11, 12).

If you don’t adjust your calorie level down in response, this will put an end to your weight loss efforts.

Strength training, by building muscle, will help to keep your RMR up. Strength training ensures that you don’t lose muscle while you diet and exercise (13).

The bottom line: If you lose weight through cardiovascular exercise and/or diet, you risk losing muscle mass in addition to fat mass. Strength training is a proven way to retain your lean muscle mass while losing fat.

Strength training burns calories even after your workout is over

The more muscle that you have, the more calories you will burn not only during exercise, but also afterward when muscle tissue is using calories to rebuild itself.

After you get done exercising, your metabolic rate stays elevated for a while. This is called post-exercise oxygen consumption (EPOC).  Several studies have shown that strength training causes elevated EPOC and increased metabolic rate.

One interesting study compared calories burned following weight training and cardiovascular exercise at the same intensity level. In the first 30 minutes following exercise, weight training resulted in a higher EPOC than cardiovascular exercise (14).

Research also shows that people burn more calories and break down more fat tissue after engaging in strength exercises targeting larger muscles (leg press) as compared to strength exercises targeting smaller muscles (chest fly). While not the finding of this study, it does suggest that having more muscle mass overall might increase EPOC (15).

In addition to increasing post-workout metabolism, strength training may affect metabolic rate even a day later. In one study, RMR was 4.2% higher 16 hours after doing 100 minutes of strength training. Fat tissue breakdown was also still significantly higher (16).

While the number of calories burned post-workout likely depends on body composition and workout intensity and length, it’s nice to know that your muscles are still working for you even after your workout is over.

The bottom line: Strength training results in increased calorie burn post-workout, in addition to during the workout. Some studies show that it may increase post-workout metabolic rate as much as cardiovascular exercise.

Strength training also fights muscle loss as we age

As we get older, we lose muscle mass. This loss of muscle, strength and function as we age is called sarcopenia.

Severe sarcopenia affects balance and gait, making falls and other accidents more likely. It also affects our ability to carry out everyday tasks and may eventually contribute to loss of ability to live independently.

Muscle mass typically declines 3 to 8% each decade after age 30, and increases to 5 to 10% lost each year after age 50 (17, 18).

This muscle loss contributes to decreasing RMR as we age. It is part of an overall loss of fat-free mass (mass from skeletal muscle, organs, skeleton, cartilage, connective tissue, lymph and plasma) that occurs as we age.

If your RMR decreases as you age, but you fail to lower your calorie intake, weight gain will result.

Although sarcopenia is seen most commonly in inactive people, even people who are physically active their whole lives are affected by it (19).

This is because there are other changes happening in our bodies as we age that contribute to muscle loss as well:

  • Hormone levels change
  • Dietary protein requirements change
  • Motor neurons die
  • We tend to become more sedentary

Research shows that strength training is an extremely effective way to minimize muscle loss. It increases muscle protein synthesis, increases communication between the brain and muscles, and improves hormone levels (20, 21).

Studies have shown that a single session of strength training can increase muscle protein synthesis two- to threefold (22, 23).

A study in elderly sedentary individuals reported that after 6 weeks of strength training (two to three sessions per week), they were able to gain up to more than 50% muscle strength (24). Strength training can increase muscle mass in adults of all ages – even through the tenth decade of life (25).

The bottom line: Unless we strength train our whole lives, muscle loss (sarcopenia) is virtually inevitable as we age. Strength training is an extremely effective way to prevent muscle loss. Research shows that it can increase muscle strength even in the very elderly.

Strength training fights weight gain as we age

In addition to losing muscle, most of us gain weight as we age.

Starting in their 30s, people gaining an average of 1 to 2 pounds per year (26). If you gained 1 pound over the course of a year, it’s likely that you wouldn’t even notice. And if you did notice, you probably wouldn’t be overly concerned.

Before you know it, however, 10 years have passed, you’ve gained 10 pounds, and your favorite jeans don’t fit anymore. Because of the way it sneaks up on us, this type of slow weight gain as we age is sometimes called “weight creep.”

Weight creep results from muscle loss as we age, along with changing hormone levels and less physical activity.

Gaining 1 to 2 pounds each year may not sound like much, but research has shown that over time it can lead to obesity (27).

Even though skeletal muscle only uses about 5 to 7 calories per pound per day, weight creep is another reason that even that small amount can make a difference. If you gain 2 pounds over a year, that means that you’ve taken in an excess of about 7000 calories in that year. That’s an average of an extra 19 calories per day. If you have are able to build (or keep) a few pounds of muscle that you would have otherwise lost due to aging, those muscles would burn about 18 calories per day at rest, not to mention the calories that you burn exercising to get/keep those muscles.

The point is, even though skeletal muscle at rest doesn’t increase metabolic rate by a huge amount, it can go a long way in combatting the calorie excess the most of us don’t even realize we are taking in.

In that way, it’s a little extra insurance against those time when perhaps we don’t exactly stick to our diet plan.

The bottom line: After the age of 30, people gain an average of 1 to 2 pounds each year. This slow gain can result in obesity over time, putting us at risk of many chronic diseases. Strength training, by increasing metabolic rate even by a small amount, can fight this slow weight gain.

Strength training lowers risk of disease

Many studies have shown that people with greater muscular strength are at lower risk of chronic diseases, including:

  • cardiovascular disease
  • stroke
  • high blood pressure
  • metabolic syndrome
  • type 2 diabetes
  • dementia and Alzheimer’s

Below are just a few examples of the effects of strength training on chronic disease.

Strength training and cardiovascular disease

A study of over 38,000 men found that those who had greater muscle strength in adolescence were at a 12% lower risk for cardiovascular disease during middle age, even when other risk factors were taken into account (28).

Strength training and blood cholesterol levels

Strength training also benefits cholesterol levels. It may decrease LDL cholesterol by 13 to 23%, decrease triglycerides by 11 to 18% and increase HDL (good) cholesterol by 8 to 21% (29).

Strength training and blood pressure

It’s well-known that aerobic exercise can help lower blood pressure, but recent evidence indicates that strength training might be equally as effective.

Both types of strength training – dynamic and isometric – can lower blood pressure. Isometric strength training may be the most beneficial. It has been shown to lower systolic blood pressure an average of 6.2 mm Hg (30).

A recent analysis of 64 controlled studies reported that, among middle-aged people with pre-hypertension, dynamic strength training 3 days/week lowered blood pressure an average of 5.1 mm Hg (31).

Strength training and metabolic syndrome

A randomized controlled study reported that a 12-week strength training program decreased risk factors for metabolic syndrome in older women. Women in the training group had significantly lower blood sugar levels, waist circumference, blood pressure, and inflammation as compared to women who did not do strength training (32).

Strength training and type 2 Diabetes

Strength training is also associated with better insulin response, lower AICs (a measure of blood sugar over time), and lower levels of abdominal fat (25).

Researchers have concluded that strength training may be an effective way to prevent type 2 diabetes (33).

Strength training, dementia, and Alzheimer’s

Studies among older adults have found that those who have low muscle strength are at increased risk for dementia, Alzheimer’s disease and Parkinson’s disease (34, 35).

One study of over 800 older adults reported that for each pound of grip-strength lost per year, risk of Alzheimer’s increased by about 9%. Other risk factors for the disease were similar between those who developed Alzheimer’s and those who didn’t (36).

The bottom line: There is an abundance of evidence that strength training lowers risk of diseases including cardiovascular disease, metabolic syndrome, type 2 diabetes, and Alzheimer’s. In addition, it can lower blood pressure and improve cholesterol levels.

Strength training can even help you live longer

Many studies have found that adults with greater muscular strength are likely to live longer than those with less muscular strength (37, 38).

In research studies, handgrip-strength is often used as a stand-in for overall muscular strength, because it’s easy to measure and is a good indicator of overall strength (39).

One study of over 2,000 men found that those who lived to be at least 100 years old were 2.5 times as likely to have had strong handgrip-strength in middle age, compared to those who died younger (39).

In a study of women, those with the lowest level of grip-strength were more than twice as likely to die from cardiovascular disease as those with the highest grip-strength. They were also about 75% more likely to die from any cause during the 5-year follow-up period than women with the highest grip-strength (40).

These findings hold true even after taking cardiorespiratory fitness, age and body fat into account.

The bottom line: Many studies have shown that older adults with less muscular strength are at increased risk of dying. Strength training can help older adults to gain muscle and could lower their risk of death.

Conclusion

While skeletal muscle doesn’t increase your resting metabolic rate that much, there are many other reasons to include strength training in your routine.

If you are trying to lose weight through cardiovascular exercise and diet alone, you risk losing muscle as you lose weight. Strength training ensures that you lose fat, rather than muscle. Retaining muscle keeps your metabolism from falling quite so much as you lose weight.

Strength training may also lower risk of cardiovascular disease, metabolic syndrome, type 2 diabetes, and Alzheimer’s disease. In addition, it’s been shown to decrease blood pressure and improve cholesterol levels.

It may even help you live longer. Older adults with greater muscle strength are at lower risk of dying than those with less muscle strength.

So, while strength training may not increase your RMR much, it can improve your health and quality of life overall. And, I would argue, that’s much more important.

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