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.

Fat infiltration within the fascial envelope of the thigh or intermuscular adispose tissue (IMAT), has been shown to be associated with both adverse metabolic and mobility impairments in older individuals. More recent findings suggest these fat deposits may be associated with increasing age and inactivity; and perhaps exercise may be able to counter or mitigate this increase in IMAT. This brief report summarizes the literature with respect to IMAT and its relationship to increasing age, physical activity levels, muscle strength, mobility and metabolism in the elderly. Further, we present preliminary data suggesting that IMAT is associated with increasing age in individuals across disease states (r=0.47, p<0.05), and that resistance exercise can decrease IMAT in older individuals with a variety of co-morbid conditions.

Objective. Intramuscular adipose tissue (IMAT) and sarcopenia may adversely impact mobility function and physical activity. This study determined the association of locomotor muscle structure and function with mobility function in older adults.Method. 109 older adults with a variety of comorbid disease conditions were examined for thigh muscle composition via MRI, knee extensor strength via isometric dynamometry, and mobility function. The contribution of strength, quadriceps lean tissue, and IMAT to explaining the variability in mobility function was examined using multivariate linear regression models.Results. The predictors as a group contributed 27–45% of the variance in all outcome measures; however, IMAT contributed between 8–15% of the variance in all four mobility variables, while lean explained only 5% variance in only one mobility measure.Conclusions. Thigh IMAT, a newly identified muscle impairment appears to be a potent muscle variable related to the ability of older adults to move about in their community.

The number of total knee arthroplasty (TKA) surgeries performed each year is predicted to steadily increase. Following TKA surgery, self-reported pain and function improve, though individuals are often plagued with quadriceps muscle impairments and functional limitations. Postoperative rehabilitation approaches either are not incorporated or incompletely address the muscular and functional deficits that persist following surgery. While the reason for quadriceps weakness is not well understood in this patient population, it has been suggested that a combination of muscle atrophy and neuromuscular activation deficits contribute to residual strength impairments. Failure to adequately address the chronic muscle impairments has the potential to limit the long-term functional gains that may be possible following TKA. Postoperative rehabilitation addressing quadriceps strength should mitigate these impairments and ultimately result in improved functional outcomes. The purpose of this paper is to describe these quadriceps muscle impairments and discuss how these impairments can contribute to the related functional limitations following TKA. We will also describe the current concepts in TKA rehabilitation and provide recommendations and clinical guidelines based on the current available evidence. Therapy, level 5.