title: Muscle Characteristics and Substrate Energetics in Lifelong Endurance Athletes.
abstract: OBJECTIVE
  The goal of this study was to explore the effect of lifelong aerobic exercise (i.e., chronic training) on skeletal muscle substrate stores (intramyocellular triglyceride [IMTG] and glycogen), skeletal muscle phenotypes, and oxidative capacity (ox), in older endurance-trained master athletes (OA) compared with noncompetitive recreational younger (YA) athletes matched by frequency and mode of training.
  
  
  METHODS
  Thirteen OA (64.8 ± 4.9 yr) exercising 5 times per week or more were compared with 14 YA (27.8 ± 4.9 yr) males and females. IMTG, glycogen, fiber types, succinate dehydrogenase, and capillarization were measured by immunohistochemistry in vastus lateralis biopsies. Fat-ox and carbohydrate (CHO)-ox were measured by indirect calorimetry before and after an insulin clamp and during a cycle ergometer graded maximal test.
  
  
  RESULTS
  V˙O2peak was lower in OA than YA. The OA had greater IMTG in all fiber types and lower glycogen stores than YA. This was reflected in greater proportion of type I and less type II fibers in OA. Type I fibers were similar in size, whereas type II fibers were smaller in OA compared with YA. Both groups had similar succinate dehydrogenase content. Numbers of capillaries per fiber were reduced in OA but with a higher number of capillaries per area. Metabolic flexibility and insulin sensitivity were similar in both groups. Exercise metabolic efficiency was higher in OA. At moderate exercise intensities, carbohydrate-ox was lower in OA but with similar Fat-ox.
  
  
  CONCLUSIONS
  Lifelong exercise is associated with higher IMTG content in all muscle fibers and higher metabolic efficiency during exercise that are not explained by differences in muscle fibers types and other muscle characteristics when comparing older with younger athletes matched by exercise mode and frequency.
authors.affiliation: 1Division of Endocrinology and Metabolism, Department of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh, PA; and 2Department of Physiology & Institute of Sport Sciences, School of Biology and Medicine, University of Lausanne, Lausanne, SWITZERLAND.
authors.forename: John J
authors.initials: JJ
authors.lastname: Dubé
authors.forename: Nicholas T
authors.initials: NT
authors.lastname: Broskey
authors.forename: Alex A
authors.initials: AA
authors.lastname: Despines
authors.forename: Maja
authors.initials: M
authors.lastname: Stefanovic-Racic
authors.forename: Frederico G S
authors.initials: FG
authors.lastname: Toledo
authors.forename: Bret H
authors.initials: BH
authors.lastname: Goodpaster
authors.forename: Francesca
authors.initials: F
authors.lastname: Amati
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D056352:Athletes; D050260:Carbohydrate Metabolism; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D007333:Insulin Resistance; D050356:Lipid Metabolism; D008297:Male; D008875:Middle Aged; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000098:blood supply / Q000378:metabolism*; D010101:Oxygen Consumption; D010807:Physical Endurance; D014280:Triglycerides / Q000378:metabolism*; D055815:Young Adult
chemical_list: D014280:Triglycerides; D006003:Glycogen