The Undervalued Medical Power of Muscle

The exponential rise of our aging population. The pandemic. The explosion of GLP-1s. It’s a trifecta that’s making muscle — and the serious implications of not having enough of it — part of a larger health conversation.

Yet when I recently asked my 65-year-old mom whether her doctor had ever talked to her about resistance training or protein intake, I was surprised to hear that the topic wasn’t coming up. (And for the record: My parents’ doctor has always been an attentive, caring, and in-the-know practitioner.) 

“Muscle span” and “strength span” aren’t just trendy new buzzwords being used to shill protein powder on Instagram. A growing body of research has strengthened the case for the unique and protective benefits of building and maintaining muscle mass over your lifespan.

“Because of the importance of muscle, both as a functional organ and as a metabolic organ, muscle depletion (or low muscle mass) is an independent predictor of poor health outcomes,” said Carla Prado, PhD, RD, director of the Human Nutrition Research Unit at the University of Alberta in Edmonton, Alberta, Canada.

Sure, you say, it’s true and makes sense, but try motivating unmotivated patients to strength train. Exercise adherence is historically one of the biggest challenges. (Roll out the standard stat that fewer than a quarter of Americans get the recommended two strength-training sessions per week, according to the CDC.)

So let’s talk about muscle — as a reminder and motivator — and while looking good at the beach takes up a lot of oxygen in that conversation, the plain truth is what muscle does on the inside is more important than what people see on the outside.

The Massive Lift of Muscle 

Skeletal muscle is the largest organ in the body by mass, taking up 30%-50% of our total body mass depending on age, sex, and fitness level. It’s not slacking off, either. While its performance benefits are obvious, skeletal muscle is an endocrine organ with wide-reaching effects on the body — from metabolic function, hormonal regulation, and disease prevention.

One of the most important roles it plays is in glucose metabolism. Skeletal muscle regulates more than 75% of insulin-mediated glucose disposal, helping control glucose and lipids while reducing the risk for metabolic diseases like type 2 diabetes. (Conversely, the loss of muscle mass — particularly as we age — leads to reduced glucose clearance from the bloodstream, increasing the risk for metabolic disorders.)

Muscle mass is a heavy hitter when it comes to our daily calorie burn, too. Our resting energy expenditure is the biggest piece of the metabolic puzzle, with the thermic effect of food and the energy expenditure from exercise playing far smaller supporting roles. And while the energy used by our brain, skin, and internal organs doesn’t vary a ton, the calories tied to muscle metabolism can shift the equation considerably.

Case in point: The average muscle mass of a young, healthy man ranges from 35 to 50 kg (77 to 110 lbs). An elderly woman? Maybe 13 kg (29 lbs). That means the energy released per day as a result of muscle protein synthesis can range from 485 calories per day (in the muscular young man) to 120 calories per day (in an active elderly woman). A 365 calorie difference.

Researchers stress that even small differences in lean mass — say, 10 kg (22 lbs) —translates to a 100-calorie difference in energy expenditure per day, which if held consistent comes out to a little over 10 pounds of fat mass per year.

“Muscle is truly valuable and we need to be figuring out how to maintain it as much as we can throughout our lives,” said Board-Certified Family Medicine Doctor (and viral social media influencer) Mikhail Varshavski. 

The problem? Adults reach peak muscle mass levels somewhere between our 20s and 40s — before it begins to progressively decline. On average, humans lose 0.5% of their skeletal muscle mass per year in their 40s, 1-2% after age 50 years, and approximately 3% per year after age 60 years.

Without proper nutrition and exercise interventions, this progressive loss of muscle mass and strength with age — better known as sarcopenia and dynapenia — can have massive consequences.

We’re not talking about struggling to screw a lid off a jar, walk up a flight of stairs, or show off our wash-board abs, either. Sarcopenia is a major contributor to frailty, falls, and loss of independence in older adults. 

Age and frailty have become a wild card in this discussion, as well, as frailty rates in the US have crept upward, for sure, but more problematic is that frailty and prefrailty are now more common in younger people. We’re becoming physically compromised at younger and younger ages.

“Survival is shorter for people with low muscle mass across the continuum of care — whether they are older adults, hospitalized patients, or patients with cancer or liver diseases,” said Prado. “If they are hospitalized, for example, they are more likely to develop complications and stay at the hospital for longer periods of time.”

This is largely due to skeletal muscle’s role as the center of protein and amino acid metabolism in the body, said Robert Wolfe, PhD, director of the Center for Translational Research in Aging and Longevity at the Reynolds Institute on Aging in Little Rock, Arkansas.

During periods of stress, trauma, or illness, muscle can be broken down to supply the body with necessary proteins for immune function and tissue repair. Individuals with limited reserves of muscle mass respond poorly, explained Wolfe.

“For example, survival from severe burn injury is lowest in individuals with reduced lean body mass,” he said. “Loss of muscle mass is also known to be detrimental to survival from cancer: In patients with lung cancer receiving radiation therapy, the amount of body protein predicted recurrence.”

Herein lies the rub: We can’t predict when an accident or critical illness may hit, yet the state of our skeletal muscle at that time can play a dramatic role in our recovery. “If there is a preexisting deficiency of muscle mass before trauma, the acute loss of muscle mass and function may push an individual over a threshold that makes recovery of normal function unlikely to ever occur,” said Wolfe. This is why 50% of women 65 years old or older who break a hip in a fall never walk again.

The takeaway? “We’re all going to lose muscle as we age, but not all of us will reach the threshold below which is associated with clinical implications,” said Prado. “That’s what we’re trying to avoid here.”

How to Hold On

Maintaining muscle demands early and proactive interventions, as age-related anabolic resistance is inevitable without it.

“While it can be somewhat reversed in those who are anabolically resistant, it can be mostly avoided by adopting a lifelong approach to muscular health,” said Brad Schoenfeld, PhD, researcher and professor of exercise science at Lehman College in New York City. “This involves regular resistance training and consuming adequate dietary protein.” 

Not cardio? While cardiovascular exercise has been much more well researched over the years and indisputably has powerful effects on your health, strength training goes well beyond what you can achieve through aerobic training.

“In my opinion, resistance training is one of the most important interventions you can do for overall health and wellness,” said Schoenfeld. “It positively affects virtually every organ system and is key to preventing a loss of physical independence as we age.”

For starters, resistance training directly stimulates mitochondrial biogenesis and improves mitochondrial function, he said. Mitochondria are critical for energy production, and their decline is linked to aging and chronic disease. Resistance training helps maintain mitochondrial health by increasing both the number and function of mitochondria in muscle cells. This has been shown to improve energy metabolism and reduce oxidative stress. For older adults, this can translate to not only better endurance but also a lower risk for metabolic diseases and improved longevity.

Resistance training is strongly linked to the prevention and management of osteoporosis, as well. The mechanical load placed on bones during resistance exercises stimulates bone remodeling and increases bone mineral density (BMD). Numerous studies have shown that resistance training is effective in preventing osteoporosis and reducing the risk for fractures in older adults. While weight-bearing exercises like walking and running are beneficial, resistance training targets areas at high risk for fractures, such as the hips and spine, making it a key intervention for maintaining bone health.

​​Skeletal muscle is also a major regulator of inflammation. During exercise, muscles release myokines, such as interleukin-6, which have anti-inflammatory effects. These myokines help regulate the immune system, improve fat metabolism, and contribute to better metabolic health. This means that beyond strength and mobility, muscle health plays a key role in modulating chronic, low-grade inflammation — a driver of many age-related diseases including cardiovascular disease, arthritis, and Alzheimer’s disease.

And despite cardio getting all the glory when it comes to heart health, a 2023 study in Sports Medicine revealed that low to moderate load resistance training has been associated with lower rates of adverse cardiovascular complications than aerobic exercise in older adults with cardiovascular disease. In fact, with strength and skeletal muscle independently associated with risk for cardiovascular disease and mortality, researchers posit that resistance training is an important interventional strategy for mitigating cardiovascular risk.

Challenges in Care

Impressive results in a research setting is one thing. Achieving them in the real world? Way tougher, of course.

Varshavski has some doubts when it comes to the realities of monitoring muscle mass or using it as a vital sign in the same way we use measures like heart rate and blood pressure. “I don’t think we have enough evidence to say we have a method to do this well,” he said. “It definitely needs to be incorporated and we perhaps have neglected it at times, but to say that it will be at the forefront of all the things that ail us — I think that’s jumping the gun.”

It doesn’t need to be the holy grail, but the evaluation of muscle health needs to be an important piece of the puzzle, said Prado. “I think that every healthcare professional has the duty to look into it.” 

More techniques are becoming available from dual-energy x-ray absorptiometry and bioelectrical impedance, to surrogate assessments such as calf circumference. Even simple questions (“Do you do any form of resistance training?”) or screening tools (like observing patients’ mobility) can go a long way to establishing a baseline.

One simple measure is grip strength, using an inexpensive dynamometer to monitor progress over time. Grip strength can be a decent proxy for overall strength, though not muscle mass.

These are imperfect measures and estimates, for sure. “But as my dear colleague Dr Christina Gonzalez likes to say: Instead of taking a picture, we can make a movie,” said Prado. “So even techniques that have some limitations, if we’re looking at change over time, some of those limitations will be offset.”

In other words, let’s not let perfect be the enemy of good.

Getting the Gains

Shifting into a more pro-muscle mentality will take time and adherence — both for practitioners and patients. “When you make one change here, it has drastic implications everywhere else,” said Varshavski. “That’s why it’s important when we’re talking with patients about the need for muscle, we talk about how it helps all parts of the body — how it can help them stay independent, help them stay mobile.”

“When it comes to muscle, what’s interesting is that we’ve seen it be a protective factor in aging and in disease prevention (or at least, lower risk evaluation for disease) irrespective if someone perhaps doesn’t have a healthy BMI,” he continued. “That sort of paradoxical relationship gets people excited and allows them to listen in.”

It’s no secret many physicians don’t get into specifics with patients on what they should be doing. One survey showed exercise prescribing rates as low as 17% with 84% of doctors saying they felt inadequately trained in the subject of resistance training. Referrals to other pros with strength training backgrounds, particularly physical therapists, can help. (See also: Medscape’s “How to Prescribe Exercise in 5 Steps”).

Schoenfeld’s research (he’s published more than 300 studies) reveals two key areas that may make strength training more palatable to patients: First, data now shows that using lighter weights can build just as much strength as heavier weights, so long as the lifter pushes to near failure in the last few repetitions (aka “the hard reps.”) So there is no barrier to entry for folks who can’t lift, or may be intimidated by heavy weights.

And second: It’s never too late to start. In a meta-analysis of adults aged 70 years or older (including nonagenarians), Schoenfeld’s team saw profound improvements in muscle strength and muscle hypertrophy within 8- to 12-week training programs. “These were novice trainees who’ve never done anything before,” he said.

Important caveat: It’s always better to start today. Because while you can always improve on where you are at a given point in time, once you start losing, it’s harder to get it back.

“The analogy I like to use is having a retirement account,” he said. “Yeah, it’s never too late to start, technically. But if you start when you’re in your 50s, your retirement isn’t going to be what it is if you start in your 20s.”