Differential Relationship between Thigh and Calf Intermuscular Adipose Tissue Depots and Muscle Compartments with Indices of Cardio‐metabolic Health
Authors: Bergia Robert Emerson , Kim Jung Eun , Campbell Wayne W 
Published: November 2023

IntroductionAccumulation of intermuscular adipose tissue (IMAT) is positively associated with insulin resistance, but there are limited data comparing the predictive ability of different IMAT stores to influence markers of cardio‐metabolic health. Investigation into the potential of IMAT to preferentially infiltrate muscle compartments with disparate muscle fiber type predominance is warranted.PurposeThe purpose of this secondary analysis study was to investigate associations among thigh and calf IMAT stores and indices of cardio‐metabolic health in adults who are overweight and obese. A subset of calf data were analyzed to assess relations between IMAT in the gastrocnemius (Type II fiber predominance) and soleus (Type I fiber predominance) with markers of cardio‐metabolic health.MethodsOne hundred and thirteen subjects (39 men, 74 women, mean ± SD, age: 50 ± 16 y (range: 21–77 y), BMI: 31 ± 3 kg/m2) completed dietary interventions with or without energy restriction‐induced weight loss and thigh and calf compositions were assessed via magnetic resonance imaging. A subset of data (n=38) were analyzed for relations between muscle compartments (gastrocnemius and soleus) and cardio‐metabolic health. IMAT was regressed separately against fasting serum glucose, insulin, homeostatic model assessment‐insulin resistance (HOMA‐IR), and lipid‐lipoprotein profile parameters. A multiple linear regression modeling procedure was performed on baseline (adjusted for age and sex) and change values (adjusted for age, sex, baseline dependent variable) and adjusted regression coefficients (β*) are reported. Significance level was set at p<0.05 and all β* values herein meet significance.ResultsIn general, thigh IMAT was predictive of metabolic health parameters, while total calf IMAT was not. Also, changes in thigh and total calf IMAT did not predict improvement in metabolic health, whereas changes in IMAT of specific calf muscle compartments were predictive of improvement in lipid‐lipoprotein profile. Specifically, baseline thigh IMAT was positively associated with fasting serum insulin, HOMA‐IR, total cholesterol (TC):HDL‐C ratio, serum triglycerides (TG), and inversely associated with HDL‐C. There were no associations between baseline total calf IMAT variables and cardio‐metabolic health indexes. No associations were detected between changes in both thigh and total calf IMAT and changes in cardio‐metabolic health indices. Changes in the soleus and gastrocnemius IMAT were predictive of changes in serum TG, TC, LDL‐C, and TC:HDL‐C ratio.ConclusionsThese data support the consensus that IMAT is associated with insulin resistance, and suggests IMAT may affect lipid‐lipoprotein profile. While improvement in cardio‐metabolic health indexes is poorly predicted by changes in IMAT of the major muscle groups, compartment‐specific IMAT reductions predict improvement in lipid‐lipoprotein profile in adults who are overweight and participating in weight loss dietary interventions. Future research should consider compartment‐specific analysis of muscle groups to assess the effect of IMAT on cardio‐metabolic health.Support or Funding InformationSupported by: Purdue Center for Aging and Life Course – Lynn Fellowship, American Egg Board – Egg Nutrition Center, Purdue Ingestive Behavior Research Center, Beef Checkoff, Pork Checkoff, National Dairy Council, NIH UL1TR001108