Muscle Mass, Quality, and Composition Changes During Atrophy and Sarcopenia

Area of Science:

• Gerontology
• Human Physiology
• Biomedical Engineering

Background:

• Skeletal muscle mass (SMM) and strength peak in adulthood and decline with age.
• Muscle strength decreases at a rate 2-4 times faster than SMM, leading to reduced normalized muscle force.
• Aging involves changes in muscle composition, including decreased muscle cell mass (MCM) ratio and increased extracellular water (ECW).

Purpose of the Study:

• To explore the relationship between aging, skeletal muscle mass, and muscle strength.
• To investigate the changes in muscle composition during aging.
• To highlight the utility of advanced bioelectrical impedance techniques for assessing muscle health.

Main Methods:

• Indirect methods like CT, MRI, DXA, ultrasonography, anthropometry, and bioelectrical impedance analysis (BIA) are used to estimate SMM.
• Segmental bioelectrical impedance spectroscopy (BIS) and multifrequency BIA are employed to estimate intracellular water (ICW) and extracellular water (ECW).
• These methods assess muscle mass, quality, and composition in living organisms.

Main Results:

• Aging is associated with a decrease in the ratio of muscle cell mass (MCM) to skeletal muscle mass (SMM).
• An expansion of extracellular water (ECW) and extracellular space is observed with advancing age and declining physical function.
• Intracellular water (ICW) and ECW measurements serve as effective biomarkers for the MCM to SMM ratio in limbs.

Conclusions:

• Bioelectrical impedance spectroscopy (BIS) and similar technologies are crucial for understanding age-related muscle atrophy.
• Assessing muscle composition, including ICW and ECW, provides deeper insights than solely measuring SMM.
• These advanced assessment tools are vital for monitoring muscle health and function in aging populations.