Sarcopenia: Why We Lose Muscle Power as We Age (and What to Do About It)

Age-Related Muscle Loss

Your skeletal muscle helps you accomplish each of these tasks:

• Getting up off the floor.

• Hauling that case of water into the trunk of your car.

• Picking up little ones – pets or kids!

• Preventing a fall when you slip on black ice

We often take these abilities for granted until they begin to change. One of the reasons they become more difficult with age is a process called sarcopenia.

Sidebar: Some definitions

• Sarcopenia: Age-related loss of muscle mass. (Commonly used to describe a loss of mass and/or function - like strength and power.)

• Strength: The amount of weight you can move

• Power: How quickly you can move a given weight

  
  

As we age, we begin to lose muscle mass. In fact, inactive adults lose 3-8% of their muscle mass per decade after age 30 and the rate of decline increases later in life. During severe illness, people can lose as much as 20% of their muscle mass in just 7-10 days.

Take another look at that list of tasks above: They require more than muscle mass and they require more than strength.

They require power.

And when it comes to power, not all muscle is the same.

Our skeletal muscles are made up of a combination of Type 1 and Type 2 muscle fibers. Each one plays a different role.

Meet Your Muscle Fibers

Type 1: Slow-Twitch - The Endurance Fibers

What they’re good at:

• Standing

• Walking

• Maintaining posture

• Low-intensity activities

Why they are good at it:

• Fatigue resistant

Type 2: Fast-Twitch - The Power Fibers

What they’re good at:

• Climbing stairs

• Rising from a chair

• Carrying groceries

• Preventing a fall

• Lifting heavy objects

Why they are good at it:

• Produce force quickly

• Generate power

If you're wondering which fibers help you catch yourself when you trip, get up from the floor, or climb stairs with ease, the answer is Type 2 fibers.

👉 We don't lose these muscle fibers equally - Fast-twitch muscle fibers atrophy first.

Sarcopenia: Fast-Twitch Muscle Fibers Are The First To Go

As we age, fast-twitch muscle fibers are naturally more vulnerable to decline. Some of this is a natural consequence of aging. Some of it is due to disuse, since we tend to gravitate toward less dynamic movement as we age. And the messaging we often receive from clinicians to “just walk” and “stick with low-impact” are deeply unhelpful pieces of advice for older adults.

(Don't get me wrong - I love walking. It has a host of mental and physical benefits. But it just doesn't provide enough stimulus to maintain muscle mass, strength, power, or bone density as we age.)

Sidebar: What is a motor unit?

A motor unit consists of one nerve cell (motor neuron) and all of the muscle fibers it controls. 

A neuron is like electrical wiring carrying instructions from the brain and spinal cord to your muscles. (See graphic below). The muscle fibers are like the light bulbs. If the wiring fails, the bulbs stop working.

How fast-twitch muscle fibers begin acting like slow-twitch muscle fibers:

Step 1: The fast-twitch neuron decays - nerve supply is lost

With age and inactivity, the motor neuron breaks down leaving a group of fast-twitch muscle fibers disconnected. (See “What is a motor unit?” above.)

Step 2: A slow-twitch neuron goes on a “rescue mission”

In response, a healthy slow-twitch neuron nearby grows new branches and attaches to the abandoned muscle fibers.

Step 3: Irreversible change - A Ferrari becomes a minivan

This rescue mission saves the muscle fibers from dying, but it comes with a tradeoff: over time, those fast-twitch "power" fibers begin behaving more like slow-twitch "endurance" fibers.

🏎️ In other words, A Ferrari becomes a minivan.

You can still drive. You can still get where you need to go, but you lose speed, power, and responsiveness. (I know what I'd rather drive!)

The Role of Disuse in Sarcopenia: Why "Use It or Lose It" Is True

The effect that aging has on our very human body is unavoidable. We will inevitably experience some declines in strength and power as we get older.

The natural aging process contributes to Type 2 fast-twitch fiber loss.

Inactivity accelerates it.

With the right inputs, we can dramatically reduce age-related decline. We can choose to lean into the types of activities that signal to our body that we want those fast-twitch fibers to stick around for as long as possible.

Anabolic Resistance: Aging Muscle Needs More Stimulus (and More Protein)

As we age, our muscles become less responsive to both exercise and the protein we eat. This phenomenon, known as anabolic resistance, means that the same activities and eating habits that maintained muscle in our younger years are often no longer enough.

In practical terms, aging muscle needs a stronger signal to maintain its size, strength, and power. Older adults benefit from a training program that includes appropriately challenging strength and power exercises.

Protein becomes more important as well. Because aging muscles are less sensitive to dietary protein, older adults generally need more protein than younger adults to achieve the same muscle-building response. Current research suggests that 1.2-1.6 grams of protein per kilogram of body weight (approximately 0.54-0.73 grams per pound) is an appropriate target for most healthy older adults.

To keep the math simple:

• Lower end: Body weight × 0.5 = minimum daily protein goal

• Upper end: Body weight × 0.75 = upper daily protein target

For example, a 150-pound woman would aim for roughly 75-112 grams of protein per day.

Spreading protein throughout the day can help as well. For most women, 20-30 grams of protein per meal is a reasonable target.

👉 One final note: protein alone cannot fix muscle loss and it can't replace strength training. Exercise does the heavy lifting (pun intended!): strength and power training provide the stimulus. Protein provides the building blocks. You need both.

How to Protect Your Type 2 Fast-Twitch Muscle Fibers

Strength Train with Intention

Progressive Resistance Exercise is essential. Muscle tissue is expensive – it requires adequate stimulus (challenge) and fuel (calories and protein) in order to stay.

Resistance training:

• Preserves muscle mass

• Preserves motor units

• Improves strength

• Improves power

Include Power Work

If we want to be able to move our body quickly, we have to practice dynamic movement regularly.

Examples:

• Fast sit-to-stands or sit-to-jumps

• Plyometrics - jumping, hopping, etc. 

• Agility drills

• Power-focused strength exercises

Stay As Active As Possible During Illness or Recovery

Avoid prolonged inactivity whenever possible.

Key Takeaways

• Sarcopenia is the age-related loss of muscle mass and function.

• Not all muscle fibers are affected equally—Type 2 fast-twitch fibers are lost first.

• Type 2 fibers are responsible for power, quick reactions, climbing stairs, getting up from a chair, and helping prevent falls.

• Aging contributes to the loss of the motor neurons that control these fibers, and inactivity accelerates the process.

• Strength and power training help preserve muscle mass, motor units, and functional independence.

• Older adults generally need more protein than younger adults due to anabolic resistance.

• Much of age-related muscle loss is not inevitable. The right combination of strength training, power training, adequate protein, and regular activity can dramatically slow age-related decline.

References

• Cruz-Jentoft AJ, Bahat G, Bauer J, et al. Sarcopenia: Revised European Consensus on Definition and Diagnosis (EWGSOP2). Age and Ageing. 2019;48(1):16-31.

• von Haehling S, Morley JE, Anker SD. An Overview of Sarcopenia: Facts and Numbers on Prevalence and Clinical Impact. Journal of Cachexia, Sarcopenia and Muscle. 2010;1:129-133.

• Dent E, Morley JE, Cruz-Jentoft AJ, et al. International Clinical Practice Guidelines for Sarcopenia (ICFSR).Journal of Nutrition, Health & Aging. 2018;22(10):1148-1161.

• Cade WT, Yarasheski KE. The Role of Exercise in Maintaining Muscle Mass and Function in Older Adults.Current Opinion in Clinical Nutrition and Metabolic Care. 2006;9(1):25-30.

• Phu S, Boersma D, Duque G. Exercise and Sarcopenia. Journal of Aging Research. 2015.

• Murphy CH, Oikawa SY, Phillips SM. Dietary Protein to Maintain Muscle Mass in Aging. Current Opinion in Clinical Nutrition and Metabolic Care. 2016.

• Deutz NEP, Bauer JM, Barazzoni R, et al. Protein Intake and Exercise for Optimal Muscle Function with Aging. Clinical Nutrition. 2014;33(6):929-936.