Intramuscular Fat Infiltration Contributes to Impaired Muscle Function in COPD

Area of Science:

• Biomedical science
• Muscle physiology
• Pulmonary medicine

Background:

• Muscle weakness is a common complication in chronic obstructive pulmonary disease (COPD).
• Muscle atrophy alone does not fully account for the observed muscle weakness.
• Fat infiltration in muscles is increasingly recognized as a contributor to functional decline in aging and diseased states, including COPD.

Purpose of the Study:

• To quantify fat infiltration (muscle quality) in the lower-limb muscles of individuals with COPD and healthy older adults.
• To investigate the relationship between fat infiltration, muscle strength, and walking capacity in COPD patients.

Main Methods:

• Magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy were used to assess muscle quality.
• Participants included individuals with COPD (n=10) and matched healthy controls (n=10).
• Muscle size, strength (isokinetic and isometric peak torques), and 6-minute walk distance were also measured.

Main Results:

• Individuals with COPD exhibited significantly greater fatty infiltration in thigh and calf muscles compared to healthy controls (74-89% difference).
• Muscle atrophy was also present in the COPD group (20-25% difference).
• Intramuscular fat infiltration strongly correlated inversely with muscle strength and walking distance (r = -0.6 to -0.8), whereas muscle size showed weaker correlations (r = 0.4-0.6).

Conclusions:

• Reduced muscle quality, characterized by significant intramuscular fat infiltration, accompanies muscle atrophy in COPD.
• Fat infiltration is a key factor correlating with impaired muscle function and reduced walking capacity in COPD, and is more pronounced than atrophy.
• Comprehensive assessment of COPD exercise programs should consider both muscle size and quality (fat infiltration).