Associations between regional adipose tissue distribution and skeletal muscle bioenergetics in older men and women

Objective: Examine the association of ectopic adipose tissue (AT) with skeletal muscle (SM) mitochondrial bioenergetics in older adults. Methods: Cross-sectional data from 829 older adults ≥70 years was used. Total abdominal, subcutaneous, and visceral AT; and thigh muscle fat infiltration (MFI) was quantified by MRI. SM mitochondrial energetics were characterized using in vivo 31P-MRS (ATPmax) and ex vivo high-resolution respirometry (maximal oxidative phosphorylation (OXPHOS)). ActivPal was used to measure PA (step count). Linear regression models adjusted for covariates were applied, with sequential adjustment for BMI and PA. Results: Independent of BMI, total abdominal (standardized (Std.) β=-0.21; R2=0.09) and visceral AT (Std. β=-0.16; R2=0.09) were associated with ATPmax (p<0.01), but not after further adjustment for PA (p≥0.05). Visceral AT (Std. β=-0.16; R2=0.25) and thigh MFI (Std. β=-0.11; R2=0.24) were negatively associated with carbohydrate-supported maximal OXPHOS independent of BMI and PA (p<0.05). Total abdominal AT (Std. β=-0.19; R2=0.24) and visceral AT (Std. β=-0.17; R2=0.24) were associated with fatty acid-supported maximal OXPHOS independent of BMI and PA (p<0.05). Conclusions: Skeletal MFI and abdominal visceral, but not subcutaneous AT, are inversely associated with SM mitochondrial bioenergetics in older adults independent of BMI. Associations between ectopic AT and in vivo mitochondrial bioenergetics are attenuated by PA.