title: Contributions of working muscle to whole body lipid metabolism are altered by exercise intensity and training.
abstract: To evaluate the contribution of working muscle to whole body lipid oxidation, we examined the effects of exercise intensity and endurance training (9 wk, 5 days/wk, 1 h, 75% Vo(2 peak)) on whole body and leg free fatty acid (FFA) kinetics in eight male subjects (26 +/- 1 yr, means +/- SE). Two pretraining trials [45 and 65% Vo(2 max) (45UT, 65UT)] and two posttraining trials [65% of pretraining Vo(2 peak) (ABT), and 65% of posttraining Vo(2 peak) (RLT)] were performed using [1-(13)C]palmitate infusion and femoral arteriovenous sampling. Training increased Vo(2 peak) by 15% (45.2 +/- 1.2 to 52.0 +/- 1.8 ml.kg(-1).min(-1), P < 0.05). Muscle FFA fractional extraction was lower during exercise (EX) compared with rest regardless of workload or training status ( approximately 20 vs. 48%, P < 0.05). Two-leg net FFA balance increased from net release at rest ( approximately -36 micromol/min) to net uptake during EX for 45UT (179 +/- 75), ABT (236 +/- 63), and RLT (136 +/- 110) (P < 0.05), but not 65UT (51 +/- 127). Leg FFA tracer measured uptake was higher during EX than rest for all trials and greater during posttraining in RLT (716 +/- 173 micromol/min) compared with pretraining (45UT 450 +/- 80, 65UT 461 +/- 72, P < 0.05). Leg muscle lipid oxidation increased with training in ABT (730 +/- 163 micromol/min) vs. 65UT (187 +/- 94, P < 0.05). Leg muscle lipid oxidation represented approximately 62 and 30% of whole body lipid oxidation at lower and higher relative intensities, respectively. In summary, training can increase working muscle tracer measured FFA uptake and lipid oxidation for a given power output, but both before and after training the association between whole body and leg lipid metabolism is reduced as exercise intensity increases.
authors.affiliation: Dept. of Integrative Biology, 3060 Valley Life Science Bldg., Univ. of California Berkeley, Berkeley, CA 94720-3140, USA.
authors.forename: Anne L
authors.initials: AL
authors.lastname: Friedlander
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Jacobs
authors.forename: Jill A
authors.initials: JA
authors.lastname: Fattor
authors.forename: Michael A
authors.initials: MA
authors.lastname: Horning
authors.forename: Todd A
authors.initials: TA
authors.lastname: Hagobian
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Bauer
authors.forename: Eugene E
authors.initials: EE
authors.lastname: Wolfel
authors.forename: George A
authors.initials: GA
authors.lastname: Brooks
mesh_terms: D000293:Adolescent; D000328:Adult; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000032:analysis; D006801:Humans; D007866:Leg / Q000098:blood supply; D050356:Lipid Metabolism / Q000502:physiology*; D015227:Lipid Peroxidation; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D012039:Regional Blood Flow; D014915:Whole-Body Counting; D016526:Workload
chemical_list: D005230:Fatty Acids, Nonesterified