Evaluation of exercise and training on muscle lipid metabolism

To evaluate the hypothesis that endurance training increases intramuscular triglyceride (IMTG) oxidation, we studied leg net free fatty acid (FFA) and glycerol exchange during 1 h of cycle ergometry at two intensities before training [45 and 65% of peak rate of oxygen consumption ((V) over dot O-2pe ak)] and after training [65% pretraining (V) over dot O-2peak, same absolut e workload (ABT), and 65% posttraining (V) over dot O-2peak, Same relative intensity (RLT)]. Nine male subjects (178.1 +/- 2.5 cm, 81.8 +/- 3.3 kg, 27 .4 +/- 2.0 yr) were tested before and after 9 wk of cycle ergometer trainin g, five times per week at 75% (V) over dot O-2peak. The power output that e licited 66.1 +/- 1.1% of (V) over dot O-2peak before training elicited 54.0 +/- 1.7% after training due to a 14.6 +/- 3.1% increase in (V) over dot O- 2peak. Training significantly (P < 0.05) decreased pulmonary respiratory ex change ratio (RER) values at ABT (0.96 +/- 0.01 at 65% pre- vs. 0.93 +/- 0. 01 posttraining) but not RLT (0.95 +/- 0.01). After training, leg respirato ry quotient (RQ) was not significantly different at either ABT (0.98 +/- 0. 02 pre- vs. 0.98 +/- 0.03 posttraining) or RLT (1.01 +/- 0.02). Net FFA upt ake was increased at RLT but not ABT after training. FFA fractional extract ion was not significantly different after training or at any exercise inten sity. Net glycerol release, and therefore IMTG lipolysis calculated from th ree times net glycerol release, did not change from rest to exercise or at ABT but decreased at the same RLT after training. Muscle biopsies revealed minor muscle triglyceride changes during exercise. Simultaneous measurement s of leg RQ, net FFA uptake, and glycerol release by working legs indicated no change in leg FFA oxidation, FFA uptake, or IMTG lipolysis during leg c ycling exercise that elicits 65% pre- and 54% posttraining (V) over dot O-2 peak. Training increases working muscle FFA uptake at 65% (V) over dot O-2p eak, but high RER and RQ values at all work intensities indicate that FFA a nd IMTG are of secondary importance as fuels in moderate and greater-intens ity exercise.