Gender-specific usage of intramyocellular lipids and glycogen during exercise.
OBJECTIVE
Gender-specific differences in substrate utilization during exercise have been reported, typically such that women rely more on fat than men. This study investigated whether gender differences exist in the utilization of intramyocellular lipids (IMCL) and glycogen.


METHODS
IMCL and glycogen, as well as total fat and carbohydrate (CHO) oxidation were measured in nine males and nine females before, during, and after an endurance exercise. The trained subjects exercised on a bicycle ergometer at 50% maximal workload for 3 h. IMCL and glycogen were determined in the thigh by magnetic resonance spectroscopy. Oxygen uptake (VO(2)) and carbon dioxide production were determined by open circuit spirometry to calculate total fat and CHO oxidation. Relative power output, percent of maximum heart rate, VO(2peak), and respiratory exchange ratio were the same.


RESULTS
Average fat oxidation was the same, whereas CHO oxidation was significantly higher in males compared with females. The relative contribution of these fuels to total energy used were similar in males and females. Males and females depleted IMCL and glycogen significantly (P < 0.001) during the 3-h exercise. IMCL levels at rest (P < 0.05) and its depletion during exercise (P < 0.001) were significantly higher in males compared with females, whereas glycogen was stored and used in the same range by both genders.


CONCLUSIONS
During this 3-h exercise, energy supplies from fat and CHO were similar in both genders, and males as well as females reduced their IMCL stores significantly. The larger contribution of IMCL during exercise in males compared with females could either be a result of gender-specific substrate selection, or different long-term training habit.
Zehnder
Monica
M
Exercise Physiology, Institute for Human Movement Sciences, Swiss Federal Institute of Technology Zurich and Institute of Physiology, University of Zurich.
Ith
Michael
M
Kreis
Roland
R
Saris
Wim
W
Boutellier
Urs
U
Boesch
Chris
C
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000378:metabolism; D004041:Dietary Fats / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006003:Glycogen / Q000378:metabolism*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D050356:Lipid Metabolism / Q000502:physiology*; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D015596:Nutrition Assessment; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D012737:Sex Factors; D013177:Sports / Q000502:physiology
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D019344:Lactic Acid; D006003:Glycogen