What is Sarcopenia
Sarcopenia is a syndrome characterized by progressive and generalized loss of skeletal muscle mass, strength, and function (performance) with consequent risk of adverse outcomes including disability, falls, fractures, and mortality. 1
Definition and Core Components
Sarcopenia represents a distinct clinical entity that requires assessment of three key parameters 1:
- Muscle mass: Quantitative loss of skeletal muscle tissue below defined thresholds
- Muscle strength: Reduced force-generating capacity of muscles
- Physical performance: Impaired functional capacity and mobility
The condition is now recognized as a form of "muscle failure"—the largest body organ failing in its function—and represents a serious clinical problem that compromises healthy aging and quality of life. 2
Classification
Primary Sarcopenia
- Age-related muscle loss that begins after the fourth decade of life 3
- Approximately 8% muscle loss per decade until age 70, then accelerating to 15% per decade thereafter 4, 3
- A phenomenon of the aging process that precedes frailty 1
Secondary Sarcopenia
- Results from pathogenic mechanisms including 1, 3:
- Disease-related: Associated with chronic conditions, inflammation, or malignancy
- Activity-related: Due to disuse, immobilization, or sedentary lifestyle
- Nutrition-related: From inadequate protein/energy intake or malabsorption
Diagnostic Criteria
While diagnostic criteria are not firmly established, the ESPEN-endorsed European Working Group on Sarcopenia in Older Persons provides an algorithmic approach 1:
Muscle Mass Assessment
Measured by validated techniques 1:
- DXA (Dual X-ray Absorptiometry): Appendicular skeletal muscle mass index <7.26 kg/m² (men), <5.5 kg/m² (women)
- BIA (Bioelectrical Impedance Analysis): Measures fat-free mass
- CT (Computed Tomography): Cross-sectional area at L3 vertebra with cut-offs <50 cm²/m² (men), <39 cm²/m² (women) 5
Muscle Strength Assessment
- Handgrip strength: <30 kg (men), <20 kg (women) 1
Physical Performance Assessment
- Gait speed: <0.8 m/s or <1.0 m/s 1
- Chair standing test: Failure indicates reduced lower extremity function 1
Prevalence and Impact
The prevalence ranges from 5-10% in the general population using conservative estimates, though estimates vary from 10-40% in community-dwelling older adults depending on definitions used. 6, 7
Critical adverse outcomes include 1, 4, 8:
- Loss of functional independence and mobility
- Increased fall risk and fractures
- Physical disability and dependence
- Reduced quality of life
- Increased mortality
Pathophysiology
The condition involves multiple mechanisms 3, 9, 2:
- Progressive motoneuron loss leading to reduced muscle fiber number and size
- Inadequate reinnervation compensation by remaining motoneurons
- Chronic pro-inflammatory state and oxidative stress
- Altered muscle protein turnover with increased breakdown
- Hormonal changes affecting muscle metabolism
- Qualitative changes in posttranslational modifications of muscle proteins
Important Clinical Distinctions
Sarcopenia vs. Cachexia
Cachexia is a multifactorial wasting syndrome with involuntary weight loss and ongoing skeletal muscle loss that cannot be reversed by conventional nutrition care, typically driven by inflammatory cytokines in disease states. 1 Sarcopenia can exist independently of cachexia.
Sarcopenic Obesity
Low muscle mass combined with elevated body adiposity results in worse health outcomes than either condition alone, and muscle loss is frequently overlooked due to excess fat and extracellular water. 1, 6
Common Pitfalls
Avoid these diagnostic errors 1:
- Overlooking sarcopenia in obese patients due to preserved or elevated body weight
- Focusing solely on muscle mass without assessing strength and function
- Failing to screen surgical patients, particularly those over 75 years, who have significantly increased sarcopenia prevalence 1
- Confusing age-related muscle decline with pathological sarcopenia requiring intervention