Repeated Prolonged Exercise Decreases Maximal Fat Oxidation in Older Men.
Fat metabolism and muscle adaptation was investigated in six older trained men (age, 61 ± 4 yr; V˙O2max, 48 ± 2 mL·kg·min) after repeated prolonged exercise).



A distance of 2706 km (1681 miles) cycling was performed over 14 d, and a blood sample and a muscle biopsy were obtained at rest after an overnight fast before and 30 h after the completion of the cycling. V˙O2max and maximal fat oxidation were measured using incremental exercise tests. HR was continuously sampled during cycling to estimate exercise intensity.



The daily duration of exercise was 10 h and 31 ± 37 min, and the mean intensity was 53% ± 1% of V˙O2max. Body weight remained unchanged. V˙O2max and maximal fat oxidation rate decreased by 6% ± 2% (P = 0.04) and 32% ± 8% (P < 0.01), respectively. The exercise intensity that elicits maximal fat oxidation was not significantly decreased. Plasma free fatty acid (FA) concentration decreased (P < 0.002) from 500 ± 77 μmol·L to 160 ± 38 μmol·L. Plasma glucose concentration as well as muscle glycogen, myoglobin, and triacylglycerol content remained unchanged. Muscle citrate synthase and ß-hydroxy-acyl-CoA-dehydrogenase activities were unchanged, but the protein expression of HKII, GLUT4, and adipose triacylglycerol lipase were significantly increased.



Overall, the decreased maximal fat oxidation was probably due to lower exogenous plasma fatty acid availability and the muscle adaptation pattern indicates an increased glucose transport capacity and an increased muscle lipolysis capacity supporting an increased contribution of exogenous glucose and endogenous fat during exercise.
1Xlab, Center for Healthy Aging, Department of Biomedical Sciences, University of Copenhagen, Copenhagen, DENMARK; 2Department of Bioscience, Zoophysiology, Aarhus University, Aarhus, DENMARK; 3Department of Cardiology, University Hospital of Bispebjerg, Copenhagen, DENMARK; 4Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, SWEDEN; 5Department of Anaesthesia and Intensive Care, Karolinska University Hospital, Huddinge, Stockholm, SWEDEN; and 6Institute of Sports Medicine Copenhagen, Bispebjerg Hospital, Copenhagen, DENMARK.
Thomas
T
Morville
Mads
M
Rosenkilde
Thor
T
Munch-Andersen
Peter Riis
PR
Andersen
Katja
K
Kjær Groenbæk
Signe
S
Helbo
Marianne
M
Kristensen
Andreas
A
Vigelsø Hansen
Nick
N
Mattsson
Hanne Kruuse
HK
Rasmusen
Amelia
A
Guadalupe-Grau
Angela
A
Fago
Christina
C
Neigaard Hansen
Brigitte
B
Twelkmeyer
Jesper
J
Løvind Andersen
Flemming
F
Dela
Jørn
J
Wulff Helge
D015094:3-Hydroxyacyl CoA Dehydrogenases / Q000378:metabolism; D001786:Blood Glucose / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006593:Hexokinase / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D008049:Lipase / Q000378:metabolism; D050356:Lipid Metabolism; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism*; D009211:Myoglobin / Q000378:metabolism; D010084:Oxidation-Reduction; D010807:Physical Endurance / Q000502:physiology*; D014280:Triglycerides / Q000378:metabolism
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D051275:Glucose Transporter Type 4; D007328:Insulin; D009211:Myoglobin; D014280:Triglycerides; D019344:Lactic Acid; D006003:Glycogen; D015094:3-Hydroxyacyl CoA Dehydrogenases; D002950:Citrate (si)-Synthase; D006593:Hexokinase; D008049:Lipase