Muscle quality and age: cross-sectional and longitudinal comparisons

Area of Science:

• Gerontology
• Muscle Physiology
• Biomedical Science

Background:

• Muscle quality, defined as force per unit muscle mass, is crucial for maintaining physical function.
• Age-related changes in muscle quality are not fully understood, with conflicting results from different study designs.
• Accurate estimation of muscle mass is essential for assessing muscle quality.

Purpose of the Study:

• To investigate age-related changes in muscle quality using both cross-sectional and longitudinal analyses.
• To compare muscle quality estimates based on different muscle mass measurement methods.
• To determine the influence of study design (cross-sectional vs. longitudinal) on age-associated muscle quality findings.

Main Methods:

• Cross-sectional and longitudinal analyses from the Baltimore Longitudinal Study of Aging.
• Muscle quality assessed via isometric strength relative to muscle mass estimated by cross-sectional area (CSA) and 24-hour urinary creatinine excretion (CREAT).
• Leg muscle mass also estimated using fat-free mass (FFM) from dual-energy x-ray absorptiometry.

Main Results:

• Cross-sectional analyses showed declines in arm and leg muscle quality with age when using CSA and FFM, but not CREAT.
• Longitudinal analyses revealed no age-associated declines in arm muscle quality using CREAT or CSA.
• The observed relationship between muscle quality and aging varied significantly based on the method of muscle mass estimation and study design.

Conclusions:

• Age-related muscle quality changes are influenced by the chosen method for estimating muscle mass.
• Cross-sectional and longitudinal study designs yield different conclusions regarding muscle quality decline with age.
• Creatinine excretion (CREAT) may reflect a distinct muscle property not captured by CSA or FFM.