Endurance exercise training attenuates leucine oxidation and BCOAD activation during exercise in humans

We studied the effects of a 38-day endurance exercise training program on l eucine turnover and substrate metabolism during a 90-min exercise bout at 6 0% peak O-2 consumption ((V) over dotO(2peak)) in 6 males and 6 females. Su bjects were studied at both the same absolute (ABS) and relative (REL) exer cise intensities posttraining. Training resulted in a significant increase in whole body (V) over dot O-2peak and skeletal muscle citrate synthase (CS ; Pt 0.001), complex I-III (P < 0.05), and total branched-chain 2-oxoacid d ehydrogenase (BCOAD; P < 0.001) activities. Leucine oxidation increased dur ing exercise for the pretraining trial (PRE, P < 0.001); however, there was no increase for either the ABS or REL posttraining trial. Leucine oxidatio n was significantly lower for females at all time points during rest and ex ercise (P < 0.01). The percentage of BCOAD in the activated state was signi ficantly increased after exercise for both the PRE and REL exercise trials, with the increase in PRE being greater (P < 0.001) compared with REL (P < 0.05). Females oxidized proportionately more lipid and less carbohydrate du ring exercise compared with males. In conclusion, we found that 38 days of endurance exercise training significantly attenuated both leucine oxidation and BCOAD activation during 90 min of endurance exercise at 60% (V) over d otO(2peak) for both ABS and REL exercise intensities. Furthermore, females oxidize proportionately more lipid and less carbohydrate compared with male s during endurance exercise.