Contributions of working muscle to whole body lipid metabolism are altered by exercise intensity and training

Anne L. Friedlander, Kevin A. Jacobs, Jill A. Fattor, Michael A. Horning, Todd A. Hagobian, Timothy A. Bauer, Eugene E. Wolfel, George A. Brooks

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


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% V̇O2 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% V̇O2 max (45UT, 65UT)] and two posttraining trials [65% of pretraining V̇O2 peak (ABT), and 65% of posttraining V̇O2 peak (RLT)] were performed using [1-13C]palmitate infusion and femoral arteriovenous sampling. Training increased V̇O2 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 (≈20 vs. 48%, P < 0.05). Two-leg net FFA balance increased from net release at rest (≈-36 μmol/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 μmol/min) compared with pretraining (45UT 450 ± 80, 65UT 461 ± 72, P < 0.05). Leg muscle lipid oxidation increased with training in ABT (730 ± 163 μmol/min) vs. 65UT (187 ± 94, P < 0.05). Leg muscle lipid oxidation represented ∼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.

Original languageEnglish (US)
Pages (from-to)E107-E116
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number1
StatePublished - Jan 2007
Externally publishedYes


  • Crossover concept
  • Exercise
  • Free fatty acids
  • Regional metabolism
  • Substrate partitioning

ASJC Scopus subject areas

  • Physiology
  • Endocrinology
  • Biochemistry


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