To test the hypothesis that beta-adrenergic stimulation is required for the normal increase in oxidative capacity of respiratory and locomotor skeletal muscle in response to exercise training, we examined the effects of beta-blockade on muscle oxidative capacity in trained and sedentary rats. Thirty-four female adult Sprague-Dawley rats were randomly divided into four experimental groups: 1) trained+propranolol (TP); 2) trained + sham injection (TS); 3) sedentary + propranolol (SP); and 4) sedentary + sham injection (SS). Training increased (p < 0.05) citrate synthase (CS) activity in the plantaris (+29%) and costal diaphragm (+12%) of TS animals compared to SS animals. In contrast, training did not (p > 0.05) increase costal diaphragm CS activity in TP animals compared to the SS group. Further, although training increased (p < 0.05) plantaris CS activity in the TP group (+18%) compared to the SP group, the training-induced increase in muscle CS activity was 11% lower (p < 0.05) than observed in TS animals. Collectively, these results suggest that beta-adrenergic mechanisms may play a role in the normal training-induced increase in oxidative capacity in both respiratory and locomotor skeletal muscles.