title: Skeletal muscle size is a major predictor of intramuscular fat content regardless of age.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  These results suggest that skeletal muscle size could be a major determinant of IntraMAT content regardless of age.
authors.affiliation: Research Center of Health, Physical Fitness and Sports, Nagoya University, Furo, Chikusa, Nagoya, 4648601, Aichi, Japan, akima@nagoya-u.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Akima
authors.forename: Akito
authors.initials: A
authors.lastname: Yoshiko
authors.forename: Maya
authors.initials: M
authors.lastname: Hioki
authors.forename: Nana
authors.initials: N
authors.lastname: Kanehira
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Shimaoka
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Koike
authors.forename: Hisataka
authors.initials: H
authors.lastname: Sakakibara
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Oshida
mesh_terms: D052242:Adiponectin / Q000097:blood; D000273:Adipose Tissue / Q000033:anatomy & histology*; D050154:Adiposity / Q000502:physiology; D000368:Aged; D000375:Aging / Q000502:physiology*; D019412:Anatomy, Cross-Sectional; D001835:Body Weight / Q000502:physiology; D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis; D006801:Humans; D008055:Lipids / Q000097:blood; D008279:Magnetic Resonance Imaging; D008297:Male; D009043:Motor Activity / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology*; D009929:Organ Size / Q000502:physiology; D052097:Quadriceps Muscle / Q000033:anatomy & histology; D050151:Subcutaneous Fat / Q000033:anatomy & histology; D055815:Young Adult
chemical_list: D052242:Adiponectin; D006442:Glycated Hemoglobin; D008055:Lipids