Screening for Age-Related Skeletal Muscle Dysfunction

Overview

This pilot study will aid the development of a sonographic screening method used to obtain proxy measures of LBM and estimates of muscle composition that relate to Intramuscular adipose tissue (IMAT), lipid metabolism, and insulin resistance. Typically, age-related muscle loss is not assessed in older adults until they began to show signs of trouble managing their own lives independently. In addition to the loss of independence that is typically seen with diminished muscle mass and function (sarcopenia), age-related changes in lean body mass can have negative effects on insulin sensitivity. The investigators central hypothesis is that the muscle characteristics derived from ultrasound (US) will be significantly associated with estimates of dual energy X-ray absorptiometry (DXA) LBM, CT scan measures of IMAT, estimates of insulin homeostasis, and serum levels of inflammatory cytokines.

The primary goals of this project are to: 1) develop and validate a rapid, portable, cost-effective, screening method for sarcopenia using diagnostic ultrasound (US), and 2) determine if the US screening method provides viable estimates of intramuscular adipose tissue (IMAT) since muscle tissue age-related changes in muscle composition are associated with low muscle torque and metabolic dysfunction. The proposed US screening method may be used as a proxy measure of LBM and provide estimates of skeletal muscle composition that relate to IMAT, lipid metabolism, insulin homeostasis and inflammation - important factors that may impact impaired mobility and metabolic dysfunction in older African American Veterans. Aim 1: Determine the association between a proxy measure of LBM obtained via portable, diagnostic, musculoskeletal US and LBM as determined by dual energy X-ray absorptiometry (DXA). The working hypothesis is that a 6-muscle model of LBM derived from US and DXA LBM values will exhibit a significant positive association and attain a coefficient of determination \> .80. Aim 2: Determine the association between US echointensity features and IMAT as determined by CT scan. US echointensity values will be acquired from the rectus femoris and analyzed to determine the association with IMAT. The working hypothesis is that higher echointensity values measured with grayscale analysis will be negatively associated with the Hounsfield units obtained from the CT scan (p \< .05). Aim 3: Examine the association between US echointensity values and biologic factors that impair insulin sensitivity. Excessive IMAT and intra-myocellular triglyceride levels result in increased levels of biologic factors such as inflammatory cytokines (TNF-α and IL-6), which may affect insulin sensitivity. The investigators hypothesis is that proxy measures of IMAT via echointensity values will be positively associated with biomarkers of inflammation and insulin homeostasis.