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Am J Physiol Endocrinol Metab (August 8, 2006). doi:10.1152/ajpendo.00148.2006
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Submitted on March 29, 2006
Accepted on July 21, 2006

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

Anne L. Friedlander1*, Kevin A Jacobs2, Jill A. Fattor3, Michael A Horning3, Todd A Hagobian1, Timothy A Bauer4, Eugene E. Wolfel5, and George A. Brooks6

1 Clinical Studies Unit, VA Palo Alto Health Care System, Palo Alto, California, United States
2 Exercise and Sports Science, University of Miami, Miami, Florida, United States
3 Integrative Biology, University of California, Berkeley, California, United States
4 Medicine, University of Colorado Health Sciences Center, Denver, Colorado, United States
5 Division of Cardiology, University of Colorado Health Science Center, Denver, Colorado, United States
6 Department of Integrative Biology, University of California at Berkeley, Berkeley, California, United States

* To whom correspondence should be addressed. E-mail: friedlan{at}stanford.edu.

To evaluate the contribution of working muscle to whole-body lipid oxidation, we examined the effects of exercise intensity and endurance training (10 wks, 5 d/w, 1 hr, 75% VO2peak) on whole body and leg free fatty acid (FFA) kinetics in 8 healthy male subjects (26±1 yr, 77.4±3.7 kg, Mean±SEM). Two pre-training trials (45% and 65% VO2peak [45UT, 65UT]) and two post-training trials (65% of pre-training VO2peak [ABT], and 65% of post-training VO2peak [RLT]) were performed using [1-13C]palmitate infusion and femoral arterio-venous sampling. Training increased VO2peak by 15%, (P<0.05). Muscle FFA fractional extraction was lower during exercise (EX) compared to rest regardless of workload or training status ({approx}20% vs. 48%, P<0.05). Two leg net FFA balance increased from net release at rest ({approx}-36 µmol min-1) 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 (TMU) was higher during EX than rest for all trials and greater post-training in RLT (716±173 µmol min-1), compared to pre-training (45UT: 450±80, 65UT: 461±72, P<0.05). Leg muscle lipid oxidation increased with training at the same absolute workload (ABT: 730±163 vs. 65UT: 187±94 µmol min-1, P<0.05). Leg muscle lipid oxidation represented approximately 62% and 30% of whole body lipid oxidation at lower and higher relative intensities, respectively. 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.




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