Intramuscular fat and physical performance at the Framingham Heart Study

Area of Science:

• Gerontology
• Musculoskeletal Health
• Radiology

Background:

• Obesity is a known risk factor for physical disability.
• Intramuscular fat (IMF) is increasingly recognized as a distinct component of obesity that may mediate the relationship between excess adiposity and functional decline.
• Understanding the specific role of IMF in physical function is crucial for targeted interventions.

Purpose of the Study:

• To investigate the association between muscle attenuation, a computed tomography-derived marker of intramuscular fat, and physical function.
• To determine if these associations differ from those of visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT).

Main Methods:

• Cross-sectional analysis of paraspinous muscle computed tomography (CT) attenuation in a subgroup of the Framingham Heart Study (n=1152).
• Muscle attenuation was assessed as a proxy for intramuscular fat.
• Regressions modeled associations between muscle attenuation and mobility disability, grip strength, and walking speed, adjusting for covariates, BMI, and VAT.

Main Results:

• A decrease in muscle attenuation (indicating higher IMF) was associated with increased odds of slow walking speed (≤1 m/s) in both men and women (OR=1.29, p=0.0009), persisting after adjustments.
• In men, lower muscle attenuation was associated with decreased grip strength (decrement=1.29 kg, p=0.0005), also persisting after adjustments.
• No similar associations were observed for VAT or SAT, underscoring the specificity of IMF's impact.

Conclusions:

• Intramuscular fat is specifically associated with poorer physical function, including reduced walking speed and grip strength.
• These findings suggest that IMF, rather than overall adiposity measures like VAT and SAT, may be a more direct contributor to physical limitations.
• Targeting intramuscular fat may be a key strategy for mitigating physical disability in aging populations.