Interrelationships between muscle fibre type, substrate oxidation and body fat.
OBJECTIVE
To investigate interrelationships between muscle fibre type, respiratory exchange ratio (RER) during exercise at a fixed workload and adiposity.


METHODS
Cross-sectional study.


METHODS
21 untrained, healthy male subjects.


METHODS
Body fat composition by dual-energy X-ray absorptiometry (DEXA). Exercise test at 55% of VO2max, muscle fibre type composition, muscle NADH and citrate synthase enzyme activity levels; serum insulin, glucose and cortisol concentrations.


RESULTS
Percent body fat was inversely correlated to the proportion of type I muscle fibres (r=-0.55, P<0.02). In addition percent trunk fat was negatively correlated with percent type I fibres (r=-0.58, P<0.01) while this relationship was not present for percent leg fat. There was no relation between RER at rest or during exercise and muscle fibre type composition or percent body fat.


CONCLUSIONS
Body fat and percent type I muscle fibres were correlated, supporting skeletal muscle fibre type as a potential etiological factor in obesity. No correlation was observed between percent body fat and substrate oxidation at rest or during moderate exercise, indicating that muscle fuel substrate mix does not appear to provide a mechanism for this relation under either condition.
Helge
J W
JW
Copenhagen Muscle Research Centre, August Krogh Institute, University of Copenhagen, Denmark. Jhelge@aki.ku.dk
Fraser
A M
AM
Kriketos
A D
AD
Jenkins
A B
AB
Calvert
G D
GD
Ayre
K J
KJ
Storlien
L H
LH
D000328:Adult; D001786:Blood Glucose; D001823:Body Composition / Q000502:physiology*; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007328:Insulin / Q000097:blood; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009765:Obesity / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D011659:Pulmonary Gas Exchange; D012016:Reference Values; D012129:Respiratory Function Tests
D001786:Blood Glucose; D007328:Insulin; D009243:NAD; D002950:Citrate (si)-Synthase; D006854:Hydrocortisone