Intermuscular Fat: A Review of the Consequences and Causes

Abstract

Muscle's structural composition is an important factor underlying muscle strength and physical function in older adults. There is an increasing amount of research to support the clear disassociation between the loss of muscle lean tissue mass and strength with aging. This disassociation implies that factors in addition to lean muscle mass are responsible for the decreases in strength and function seen with aging. Intermuscular adipose tissue (IMAT) is a significant predictor of both muscle function and mobility function in older adults and across a wide variety of comorbid conditions such as stroke, spinal cord injury, diabetes, and COPD. IMAT is also implicated in metabolic dysfunction such as insulin resistance. The purpose of this narrative review is to provide a review of the implications of increased IMAT levels in metabolic, muscle, and mobility function. Potential treatment options to mitigate increasing levels of IMAT will also be discussed.

Heterogeneity of adipose tissue in development and metabolic function

“…IMAT is found beneath the fascia of skeletal muscle (Gallagher et al, 2005) and includes adipocytes between muscle groups (intermuscular), as well as adipocytes located between muscle fibers (intramuscular) (Addison et al, 2014;Gallagher et al, 2005;Karampinos et al, 2012) (Fig. 1).…”

“…IMAT accounts for ∼2-3% of total body fat in healthy lean women (Gallagher et al, 2005) and increases upon aging (Song et al, 2004), obesity (Gallagher et al, 2005) and physical inactivity and sedentariness (Elder et al, 2004;Gorgey and Dudley, 2007;Manini et al, 2007;Ryan et al, 2011Ryan et al, , 2002. Thus, it is not surprising that increased IMAT correlates with an increased risk for metabolic disease (Addison et al, 2014;Boettcher et Fig. 2.…”

Skeletal muscle mass and quality: evolution of modern measurement concepts in the context of sarcopenia

“…Skeletal muscle in persons with sarcopenia is characterised by an enlarged IMAT component, notably in the lower extremities (73,74) . Water-fat imaging has also been used to evaluate regional skeletal muscle fat infiltration, and as noted earlier, the CT# gives an indication of water and fat infiltration into skeletal muscles (76) .…”

Adiposity and spinal cord injury

“…In our laboratory (Figures 1 and 2), we have managed to distinguish between IMF, IeMF, subfacial and SAT accumulation in persons with SCI [9,10] . The storage of triglycerides in ectopic locations is linked with chronic inflammation, impaired glucose tolerance, increased total cholesterol, and decreased strength and mobility [1,2] . There is growing interest in studying different peripheral adipose tissue compartments to determine its link to metabolic profile after SCI [6,26] .…”

“…It is not only served as an energy reservoir, but it has been recently considered as the largest endocrine gland in the body [1,2] . The endocrine properties are related to the secretion of regulatory proteins similar to leptin, cytokines and adiponectin that are likely to influence whole body metabolism, energy intake as well as insulin sensitivity [2] .…”