Muscle fatty, or more accurately, muscle fat infiltration, refers to the accumulation of adipose tissue (fat) within skeletal muscle. This isn't simply having some fat around muscles; it's the infiltration of fat into the muscle tissue itself, replacing muscle fibers. This process is linked to various health issues and is different from sarcopenia (muscle loss due to aging).
Understanding Muscle Fat Infiltration
Several factors contribute to muscle fat infiltration:
- Aging: As we age, the decline in muscle and bone strength is often accompanied by an accumulation of adipose tissue within muscles. [PMC4913107]
- Metabolic Disorders: Conditions like insulin resistance, obesity, and non-alcoholic fatty liver disease (NAFLD) are associated with increased muscle fat infiltration. [10600804, 29679374, joe.bioscientifica.com/view/journals/joe/220/2/T61.xml] These conditions often disrupt the balance of fatty acid uptake and oxidation within the muscle. [10.2522/ptj.20080018]
- Muscle Degeneration: Muscle degeneration, such as that seen in low back pain, is characterized by a decrease in muscle cross-sectional area and an increase in fat infiltration. [S2589004224004425]
- Other Factors: The severity of rotator cuff tears can also influence the degree of fatty degeneration in the surrounding muscles. [14671517] Even the type of fatty acids present in muscle phospholipids can affect insulin sensitivity and may be linked to muscle fat infiltration. [8418404]
Myosteatosis: A Distinct Condition
Myosteatosis is defined as the pathologic fat accumulation in skeletal muscle with poor metabolic and musculoskeletal health. [14-Feb-2024] It's crucial to differentiate this from sarcopenia, which primarily focuses on muscle loss. Myosteatosis involves a change in muscle composition, with fat replacing muscle fibers, impacting both metabolic function and muscle strength.
Impact of Muscle Fat Infiltration
The consequences of significant muscle fat infiltration can include:
- Reduced Muscle Strength and Function: Fat infiltration replaces muscle tissue, leading to a decrease in strength and the ability to perform physical activities.
- Metabolic Dysfunction: It's linked to insulin resistance and other metabolic issues.
- Increased Risk of Chronic Diseases: It's associated with an increased risk of various health problems.
The amount of fat oxidation within muscles also plays a role, with maximal rates typically occurring at moderate exercise intensity (~60–65% VO2 max). [s42255-020-0251-4] Intermuscular adipose tissue (IMAT) also plays a role in overall health, particularly in areas like the thigh. [PMC3758242]
