Effects of exercise intensity and training on lipid metabolism in young women.

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Abstract
We examined the effects of exercise intensity and training [12 wk, 5 days/wk, 1 h, 75% peak oxygen consumption (V˙o 2 peak)] on lipolysis and plasma free fatty acid (FFA) flux in women ( n = 8; 24.3 ± 1.6 yr). Two pretraining trials (45 and 65% ofV˙o 2 peak) and two posttraining trials [same absolute workload (65% of oldV˙o 2 peak; ABT) and same relative workload (65% of newV˙o 2 peak; RLT)] were performed using infusions of [1,1,2,3,3-2H]glycerol and [1-13C]palmitate. Pretraining rates of FFA appearance (Ra), disappearance (Rd), and oxidation (Rox p) were similar between the 65% (6.8 ± 0.6, 6.2 ± 0.7, 3.1 ± 0.3 μmol ⋅ kg−1 ⋅ min−1, respectively) and the 45% ofV˙o 2 peaktrials. At ABT and RLT training increased FFA Ra to 8.4 ± 1.0 and 9.7 ± 1.1 μmol ⋅ kg−1 ⋅ min−1, Rd to 8.3 ± 1.0 and 9.5 ± 1.1 μmol ⋅ kg−1 ⋅ min−1, and Rox p to 4.8 ± 0.4 and 6.7 ± 0.7 μmol ⋅ kg−1 ⋅ min−1, respectively ( P ≤ 0.05). Total FFA oxidation from respiratory exchange ratio was also elevated after training at ABT and RLT, with all of the increase attributed to plasma FFA sources. Pretraining, glycerol Ra was higher during exercise at 65 than 45% of V˙o 2 peak(6.9 ± 0.9 vs. 4.7 ± 0.6 μmol ⋅ kg−1 ⋅ min−1) but was not changed by training. In young women 1) plasma FFA kinetics and oxidation are not linearly related to exercise intensity before training, 2) training increases FFA Ra, Rd, and Rox p whether measured at given absolute or relative exercise intensities, 3) whole body lipolysis (glycerol Ra) during exercise is not significantly impacted by training, and 4) training-induced increases in plasma FFA oxidation are the main contributor to elevated total FFA oxidation during exercise exertion after training.