Associations Of Skeletal Muscle Lipid Infiltration With Hypertrophy And Physical Performance Outcomes In Older Adults

Abstract

Preserving muscle mass and quality is critical for long term health and longevity. Unfortunately, the hypertrophic potential of aged individuals is diminished, with some experiencing less than favorable outcomes from supervised resistance training programs. This has led investigators to explore the “poor” responder muscle phenotype. PURPOSE: The purpose of this study was to determine whether muscle lipid infiltration plays a role in anabolic adaptation responses, such as muscle growth and physical performance. METHODS: The effects of a 14-week progressive resistance training (PRT) program on muscle size and quality, strength, and physical function in 48 individuals aged 65 and older (mean age ± SD, 70.8 ± 4.5 yrs) was determined. Computed tomography (CT) imaging of cross-sectional mid-thigh regions was used to measure intermuscular adipose tissue (IMAT) and thigh muscle density (TMD) as measures of thigh muscle lipid content. Associations between these lipid depots and baseline function, as well as muscle adaptations to PRT, were made for muscle size (DXA muscle mass and CT muscle area) and physical function and performance (strength, power, SF-36, PROMIS) using multiple linear regression models adjusted for potential confounders such as sex, BMI, CT muscle area, and baseline muscle strength. The association of muscle lipid and physical activity were conducted as a secondary analysis. RESULTS: At baseline, TMD (mean Hounsfield unit ± SD, 42.1 ± 4.0 HU), but not IMAT (mean area ± SD, 12.5 ± 4.3 cm2), was significantly associated with all physical function and performance variables (R2 range 0.45-0.75, p < 0.05) except leg extension strength and power. Neither IMAT nor TMD was related to physical activity. Following PRT, IMAT was not associated with any exercise adaptation, whereas TMD was negatively associated with percent change in isometric strength (R2 0.17) and muscle power (R2 0.28, p < 0.05). CONCLUSIONS: Muscle fatty infiltration can impact strength and power gains following PRT in older persons. More work is needed to understand the dynamics of ectopic muscle fat accumulation and its influence on physical function and muscle metabolism/anabolism.