The branched-chain oxo acid dehydrogenase complex (BCOAD) is rate-determining for the oxidation of branched-chain amino acids (BCAAs) in skeletal muscle. Exercise training blunts the acute exercise-induced activation of BCOAD (BCOADa) in human skeletal muscle (McKenzie et al., Am J Physiol 278: E580-E587), however the mechanism is unknown. We hypothesized that training would increase the muscle protein content of BCOAD kinase, the enzyme responsible for inactivation of BCOAD by phosphorylation. Twenty subjects [23±1 y; peak oxygen uptake (VO₂peak) = 41±2 ml/kg/min] performed 6 wk of either high-intensity interval or continuous moderate-intensity training on a cycle ergometer (n=10/group). Before and after training, subjects performed 60 min of cycling at 65% of pre-training VO₂peak, and needle biopsy samples (v. lateralis) were obtained before and immediately after exercise. The effect of training was demonstrated by an increased VO₂peak, increased citrate synthase maximal activity and reduced muscle glycogenolysis during exercise, with no difference between groups (main effects, p<0.05). BCOADa was lower after training (main effect, p<0.05) and this was associated with a ~30% increase in BCOAD kinase protein content (main effect, p<0.05). We conclude that the increased protein content of BCOAD kinase may be involved in the mechanism for reduced BCOADa after exercise training in human skeletal muscle. These data also highlight differences in models used to study the regulation of skeletal muscle BCAA metabolism, since exercise training was previously reported to increase BCOADa during exercise and decrease BCOAD kinase content in rats (Fujii et al., Biochem Mol Biol Int 44:1211-1216, 1998).