Skeletal muscle size is a major predictor of intramuscular fat content regardless of age
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Skeletal muscles of older individuals have a larger amount of intramuscular adipose tissue (IntraMAT) than those of younger individuals. It is not understood how aging affects the IntraMAT content of individual muscles of the thigh. We assessed the relationship between IntraMAT content and skeletal muscle cross-sectional area (CSA), subcutaneous adipose tissue CSA, biochemical blood profiles, and physical activity.
Fifteen older (70.7 ± 3.8 years) and 15 younger (20.9 ± 0.3 years) men and women participated in this study. Magnetic resonance imaging of the right thigh was taken to measure IntraMAT content and skeletal muscle CSA for the quadriceps femoris (QF), hamstrings (HM), adductor (AD) muscle groups and subcutaneous adipose tissue CSA of the thigh. Fasting blood samples were collected to measure plasma lipids, adiponectin, and HbA1c levels.
IntraMAT content in QF, HM, and AD for the Older group was significantly higher than in the Younger group. However, skeletal muscle CSA normalized by body weight (skeletal muscle CSA/bw) in the QF (P < 0.001) and total thigh (P < 0.01) were significantly lower in the Older group compared with the Younger group.There were no significant differences in HM and AD. Stepwise regression analysis with IntraMAT content as a dependent variable revealed that skeletal muscle CSA/bw of the thigh was the only predictive variable for IntraMAT content in Older and Younger groups.
These results suggest that skeletal muscle size could be a major determinant of IntraMAT content regardless of age.
KeywordsSkeletal muscle Sarcopenia Magnetic resonance imaging Blood lipids
Analysis of variance
Biceps femoris-long head
Free fatty acids
Intramuscular adipose tissue
Magnetic resonance imaging
The authors gratefully thank the volunteers for participation as well as Drs Haruo Isoda and Atsushi Fukuyama and Radiologic technologist Mr. Akira Ishizuka, Graduate School of Medicine, Nagoya University. This study was supported in part by a Grant-in-Aid for challenging Exploratory Research from the Ministry of Education, Culture, Sports and Science and Technology Grant (#23650432) to HA.
Conflict of interest
The authors declare no conflict of interest.
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