In this article

The short answer: Sarcopenia is the age-related loss of muscle strength and muscle quantity or quality that eventually limits everyday function (Cruz-Jentoft et al., 2019). Muscle size starts to slip in midlife, and strength tends to fall faster than size (Janssen et al., 2000; Goodpaster et al., 2006). Resistance training improves strength even in the very old (Fiatarone et al., 1994), so the practical answer to "how early" is: before you need it. Build the reserve in your 30s and 40s, protect it with regular strength work and enough protein, and avoid long stretches of inactivity.

  1. 01Definition
  2. 02Timeline
  3. 03Why It Matters
  4. 04Prevention
  5. 05How Early
  6. 06Misconception
  7. 07What To Do
  8. 08FAQ
  9. 09Key Takeaways
  10. 10References
Jump to key takeaways

What Is Sarcopenia?

Irwin Rosenberg coined the term in 1989, from the Greek for "flesh" and "loss," to describe the decline of muscle with age (Rosenberg, 1989). The current European consensus puts low muscle strength at the center of the definition. Low strength makes sarcopenia "probable," low muscle quantity or quality confirms it, and poor physical performance such as slow walking marks it as severe (Cruz-Jentoft et al., 2019).

1. Probable

Low muscle strength, usually screened with grip strength or a chair-stand test.

2. Confirmed

Low muscle quantity or quality, measured with imaging or body composition scans.

3. Severe

Low strength and low muscle, plus poor physical performance such as slow gait speed.

Sarcopenia is a clinical diagnosis. A normal-looking body weight or BMI says very little about it, which is why muscle mass is a better longevity signal than weight.

When Does Muscle Loss Start?

Earlier than most people expect, though slowly. In a whole-body MRI study of 468 adults aged 18 to 88, muscle mass relative to body size began to fall in the third decade of life, while absolute muscle mass did not drop noticeably until the end of the fifth decade, mostly in the legs (Janssen et al., 2000). Strength is the faster mover: in older adults followed for three years, leg strength fell roughly three times faster than leg lean mass, which suggests muscle quality declines on top of muscle size (Goodpaster et al., 2006).

What the timeline looks like

Young adulthood

Muscle is at or near its peak. This is the reserve you draw on later.

Third decade onward

Muscle relative to body size starts to decline (Janssen et al., 2000).

Late 40s onward

Absolute muscle mass, especially in the legs, begins to fall in a measurable way (Janssen et al., 2000).

Later life

Strength falls faster than mass (Goodpaster et al., 2006), and inactivity or illness can speed the slide.

Individual rates vary a lot with genetics, activity, nutrition, and illness, so treat these stages as a general shape, not a personal forecast.

Why Does It Matter?

Strength is a practical marker of reserve. In the PURE study of adults aged 35 to 70 across 17 countries, lower grip strength was associated with higher all-cause and cardiovascular mortality (Leong et al., 2015). That is an association, not proof that raising grip strength lowers risk. For what grip strength can and cannot tell you, see what grip strength says about longevity.

Caveat: inactivity is a fast route

Ten days of bed rest in healthy older adults cut the rate of muscle protein synthesis and was followed by lower leg strength (Kortebein et al., 2007; Kortebein et al., 2008). Illness, injury, or a long layoff can take back ground that years of slow aging did not.

What Actually Helps Prevent It?

Two levers have the best-documented support: resistance training and adequate protein. In a randomized trial of 100 frail nursing home residents with a mean age of 87, ten weeks of progressive resistance training markedly increased strength and improved walking speed, while a nutritional supplement alone did not improve strength (Fiatarone et al., 1994). Public health guidelines recommend muscle-strengthening activity on at least two days a week for adults (Bull et al., 2020).

1

Lift something challenging, twice a week or more

Work the legs, hips, back, and upper body with loads that feel hard by the last few reps, and add load or reps over time.

2

Eat enough protein

The PROT-AGE expert group suggested at least 1.0 to 1.2 g per kg of body weight per day for healthy older adults, and more for those who exercise or are ill (Bauer et al., 2013).

3

Keep daily movement up

Long stretches of sitting or bed rest drive muscle loss quickly (Kortebein et al., 2007). Walk, take stairs, and get moving again fast after illness.

4

Check strength, not just weight

A grip test, chair-stand time, or walking speed catches decline that the scale hides.

Progressive overload is how you keep adding load, covered in how to track it. Protein amounts depend on your goal and age; how much protein you need by goal goes deeper.

How Early Should You Start?

As soon as you can, and a late start still appears to help. There is no study that pins down an ideal start age, so this is a judgment call from the biology: muscle is built fastest and kept most easily when you are younger, the slow decline starts in early adulthood, and training works at every age tested, including the very old (Fiatarone et al., 1994). Starting in your 30s and 40s gives you a bigger reserve and a habit that is easy to keep. Starting at 70 still helps.

Start before you need it

Training in early and midlife builds the reserve and the habit, and is easier on joints and tendons than a late start.

Start late, still worth it

Older adults, including frail ones, gained strength from supervised resistance training (Fiatarone et al., 1994). Ease in and build gradually, as covered in the tendon resilience guide.

What Is the Most Common Misconception?

That sarcopenia only affects the very old, or that cardio and a healthy weight are enough to prevent it.

Common misconception

"My weight is normal, so my muscle is fine." Weight and BMI do not separate muscle from fat, and muscle can shrink while weight stays flat. Track strength and, if you can, muscle relative to body size, as in the muscle mass index guide.

What Should You Do Next?

Pick one strength session you can repeat, and measure something simple.

1

Schedule two strength sessions a week

Full-body sessions of squat or leg press, a hinge, a push, and a pull are enough to start.

2

Set a baseline

Note your chair-stand time, grip strength if you have a dynamometer, and how heavy your working sets are today.

3

Review every few months

Look for flat or rising strength. A falling trend is a reason to adjust training, protein, or sleep, or to talk to a clinician.

4

See a clinician if function is slipping

Difficulty rising from a chair, slow walking, or unexplained weakness deserves a proper assessment.

Frequently Asked Questions

What is sarcopenia in simple terms?

It is the age-related loss of muscle strength and muscle quantity or quality that eventually affects daily function (Cruz-Jentoft et al., 2019).

At what age does muscle loss begin?

Muscle relative to body size starts to decline in the third decade, and absolute muscle mass falls measurably from around the end of the fifth decade, mostly in the legs (Janssen et al., 2000). The pace varies widely between people.

Can you reverse sarcopenia?

Strength can improve at any age with resistance training, including in very old, frail adults (Fiatarone et al., 1994). How much muscle you regain depends on the person, the program, and the underlying causes.

How much protein helps prevent sarcopenia?

An expert group suggested at least 1.0 to 1.2 g per kg of body weight per day for healthy older adults, with more for those who exercise regularly or have illness (Bauer et al., 2013). Individual needs differ, so confirm with a clinician if you have kidney disease or another condition.

Is cardio enough?

Cardio matters for the heart, but guidelines recommend muscle-strengthening work on at least two days a week as a separate component (Bull et al., 2020).

What to remember

The short version.

  1. 1Sarcopenia is age-related loss of muscle strength and muscle quantity or quality, with low strength as the main flag (Cruz-Jentoft et al., 2019).
  2. 2Muscle relative to body size starts declining in early adulthood, and absolute muscle falls measurably from late midlife (Janssen et al., 2000).
  3. 3Strength falls faster than muscle mass, so tracking strength catches decline that weight hides (Goodpaster et al., 2006).
  4. 4Resistance training improves strength at every age studied, including in the very old (Fiatarone et al., 1994).
  5. 5Aim for strength work on at least two days a week (Bull et al., 2020) and enough protein (Bauer et al., 2013).
  6. 6Start before you need it: the earlier you build and maintain muscle, the larger your reserve, but late starts still help.

Keep reading

Related on Protocol

Protocol

Watch strength trends, not just the scale.

Protocol puts your training, protein, sleep, and recovery in one place so you can see whether your strength is holding or slipping over months.

Get started free

ReferencesSources

Key Studies

  • Janssen et al. (2000) Journal of Applied Physiology, volume 89, issue 1, pages 81 to 88. Skeletal muscle mass and distribution in 468 men and women aged 18 to 88 years, measured by MRI.
  • Goodpaster et al. (2006) Journals of Gerontology Series A, volume 61, issue 10, pages 1059 to 1064. Health ABC Study: strength declined faster than muscle mass in older adults.
  • Fiatarone et al. (1994) New England Journal of Medicine, volume 330, issue 25, pages 1769 to 1775. Resistance training and supplementation in 100 frail nursing home residents.
  • Kortebein et al. (2007) JAMA, volume 297, issue 16, pages 1772 to 1774. Effect of 10 days of bed rest on skeletal muscle in healthy older adults.
  • Kortebein et al. (2008) Journals of Gerontology Series A. Functional impact of 10 days of bed rest in healthy older adults, including lower leg strength.
  • Leong et al. (2015) The Lancet, volume 386, pages 266 to 273. Prognostic value of grip strength in the PURE study.

Reviews and Guidelines

  • Rosenberg (1989) American Journal of Clinical Nutrition, volume 50, pages 1231 to 1233. Summary comments; the term sarcopenia is attributed to this meeting.
  • Cruz-Jentoft et al. (2019) Age and Ageing, volume 48, issue 1, pages 16 to 31. EWGSOP2 revised European consensus on sarcopenia definition and diagnosis.
  • Bauer et al. (2013) Journal of the American Medical Directors Association, volume 14, pages 542 to 559. PROT-AGE evidence-based recommendations on dietary protein for older people.
  • Bull et al. (2020) British Journal of Sports Medicine, volume 54, pages 1451 to 1462. WHO guidelines on physical activity and sedentary behaviour.