Doctor of Philosophy

dissertationIntramuscular adipose tissue (IMAT) is an important negative predictor of muscle and mobility function in older adults. While IMAT has been theorized to increase with aging, more recent evidence suggests that IMAT may be a byproduct of inactivity rather than aging per se. The mechanism of IMAT's influence on muscle and mobility function is unknown but similar to the negative consequences attributed to other ectopic fat depots, may involve an inflammatory pathway. In order to clarify if IMAT is an obligatory consequence of age or if it is related to inactivity, the primary aim of this study was to compare IMAT, muscle and mobility function, and muscular inflammation in age and BMI matched older frail and nonfrail adults. A secondary aim was to examine the relationship of IMAT and visceral adipose tissue (VAT), muscular inflammation, muscle function and mobility function in a subgroup of older adults. Two groups of older nonobese adults were recruited. A sedentary frail group was classified as at least moderately frail with modified physical performance test scores of 32. Magnetic resonance imaging (MRI) was used to determine mean cross sectional area of thigh IMAT and VAT. Maximal voluntary isometric contractions were used to determine muscle function, and 6 minute walk and stair ascent time were used to determine mobility function. A sub group of participants from both groups who were free from disease and medications known to influence inflammation underwent percutaneous muscle biopsies iv of the vastus lateralis. Western blot and real time polymerase chain reaction were used to determined local muscular expression of mRNA and protein for the proinflammatory cytokines interleukin 6 (IL-6) and tumor necrosis alpha (TNF-a). We found significant differences in IMAT, and IL-6 mRNA and protein expression between frail and nonfrail adults. We also found significant correlations between IMAT, VAT, IL-6, and muscle and mobility function. These findings suggest that IMAT is a product of inactivity and disease rather then aging alone and provide a potential mechanistic link between increased IMAT and decreased muscle and mobility function in older adults

Intermuscular fat: a review of the consequences and causes

pre-printMuscle'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

Editorial: Muscle Quality in Skeletal Muscle Function Deficit: Recent Advances and Potential Clinical and Therapeutic Implications

No abstract availabl

Intramuscular Adipose Tissue, Sarcopenia, and Mobility Function in Older Individuals

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

Intermuscular Fat: A Review of the Consequences and Causes

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.</jats:p

FRAILTY

Abstract The ability to safely maintain mobility function with aging is critical as immobility and falls are among the top reasons for long-term care admissions. One potential cause for these functional deficits are muscle composition changes resulting in reductions in muscle mass, strength and power, ultimately contributing to the development of frailty. While the majority of work examining muscle composition and mobility changes with aging have focused on the quadriceps and ankle plantarflexor/dorsiflexor muscles, accumulating evidence suggests that deficits involving the proximal hip muscles may be particularly harmful to balance and mobility functions leading to falls, hip fractures, and frailty. We will discuss muscle changes that occur with aging and frailty, the implications on mobility, and the effects of potential exercise interventions on muscle structure and function as well as their ability to improve functional mobility.</jats:p

Self-Reported Physical Limitations Among U.S. Veterans Compared to Non-Veterans: Findings from NHANES

Abstract Approximately 43% of males over the age of 65 years are Veterans. Veterans may be at elevated risk for functional declines due to barriers to health care access leading to accelerated loss of independence. This compared the prevalence of functional limitations in Veterans and non-Veterans. Data from two National Health and Examination Survey collection periods, administered 2013-2014 and 2015-2016, were used to compare physical functioning data between male Veterans (N=369) and non-Veterans (N=738) matched 1:2 for sex, race, and BMI. Individuals were considered a Veteran if they self-reported having “served in active duty in the U.S. Armed forces.” Pearson’s chi-square tests were used to assess differences in the prevalence of various self-reported functional limitations between groups. Veterans (mean±SEM: age: 64.5±0.54 years; BMI: 30.0±0.3 kg/m2) were disproportionately affected by self-reported functional limitations caused by long-term physical, mental, or emotional illnesses (8% vs. 3%, p&amp;lt;0.004). Twenty-five % of Veterans reported that these limitations kept them from working compared to 18% of non-Veterans (p&amp;lt;0.003). Veterans (38%) were also more likely to report being limited in the amount of work they could perform compared to non-Veterans (27%) (p&amp;lt;0.01). Additionally, Veterans (20%) were more likely to report the use of special healthcare equipment (i.e. cane, wheelchair) than non-Veterans (12%) (p&amp;lt;0.001). These data suggest that Veterans are at greater risk for functional limitations caused by self-reported long-term physical, mental or emotional illness. Therefore, further research is needed to determine if home- and community-based services could prevent further functional decline, ultimately allowing Veterans to maintain independence.</jats:p

Self-Reported Utilization of Nutrition-Related Resources in Veterans Compared to Non-Veterans

Abstract As they age, Veterans are at elevated risk for developing nutrition-associated chronic diseases compared to their Non-Veteran counterparts. This is despite Veterans often being eligible for a variety of nutrition-related resources. This project compared self-reported utilization of community and government nutrition-related resources in male Veterans compared to Non-Veterans participating in the 2013-2014 and 2015-2016 National Health and Nutrition Examination Surveys. Veterans (mean: age: 59 years; BMI: 29 kg/m2; N=135) self-reported “yes” and Non-Veterans (age: 61 years; BMI: 30 kg/m2; N=230) self-reported “no to “ever having served on active duty in the U.S. Armed Forces.” A similar percentage of Veterans (3%) and Non-Veterans (4%) reported utilizing meal delivery programs (i.e., “Meals on Wheels) and eating at community or senior centers (both 7%) in the past year. Veterans were less likely than Non-Veterans to report receiving emergency food (i.e. from church or food bank) in the past year (7% vs. 12%; P&amp;lt;0.01) and tended to be less likely to report ever having received benefits from a nutrition assistance program (NAP; i.e., Food Stamps) (27% vs. 32%; P=0.08). Veteran also reported their household receiving more financial assistance the last time they received support from a NAP ($281 vs.$188; P=0.02). These data suggest that Veterans have less reliance on NAP than Non-Veterans; however, when they do receive assistance, Veterans appear to receive greater financial support. Future studies are needed to identifying ways to improve access to nutrition-related resources in those at risk for food insecurity.</jats:p

Sarcopenic Obesity in Older Adults: Findings From the National Health and Aging Trends Study

Abstract Sarcopenic obesity increases risk for dysmobility and loss of independence, (Gandham et al., 2021). However, the national burden of sarcopenic obesity and the resultant impacts for older adults has yet to be described. Within a nationally representative sample from the National Health and Aging Trends Study (NHATS), 2066 community-dwelling older adults were obese, representing 12,136,374 individuals in the United States, or 31.8% of all community dwelling older adults. Based on the European Working Group definition, 18% of the obese older adults were sarcopenic. Sarcopenic obese older adults were more likely to have fallen in the last month and been hospitalized over the prior year. After adjusting for age and sex, sarcopenic obese older adults were 3.7 times more likely (95% CI 2.2-5.0) to have 2 or more comorbid conditions and frailty was 6.4 times more likely (95% CI 4.4-9.5) compared to nonsarcopenic obese older adults. Sarcopenic obese older adults were also more likely to have 1+ ADL disabilities (OR 3.7; 95% CI 2.5-5.4). Further, they were more likely to be socially isolated (OR 2.1; 95% CI 1.3-3.2) and report food insecurity (OR 1.5; 95% CI 0.8-2.9). These findings suggest older adults with obesity and sarcopenia have higher rates of geriatric vulnerabilities, which might indicate a need for caution when recommending weight loss alone as an intervention. A more comprehensive intervention may be necessary to address social and physiological risks. Future studies should examine whether early intervention in sarcopenic obese older adults can reduce chronic health risk and preserve independence.</jats:p