Norepinephrine response to exercise at the same relative intensity before and after endurance exercise training

It is well documented that endurance exercise training results in a blunted norepinephrine (NE) response to exercise of a given absolute exercise intensity. However, it is not clear what effect training has on the catecholamine response to exercise of the same relative intensity because previous studies have provided conflicting results. The purpose of the present study was, therefore, to determine the catecholamine response to exercise of the same relative exercise intensity before and after endurance exercise training. Six women and three men [age 28 ± 8 (SD) yr] performed 10 wk of training. Maximal O₂ uptake (V̇O(2max)) was determined during treadmill exercise. Fifteen-minute treadmill exercise bouts were performed at 6.0, 65, 70, 75, 80, and 85% of V̇O(2max) before and after training. V̇O(2max) was increased by 20% (from 39.2 ± 7.7 to 46.9 ± 8.1 ml · kg^{- 1} · min^-1; P < 0.05) in response to training. Plasma NE concentrations were higher (P < 0.05) during exercise at the same relative intensity after, compared with before, training at 65-85% of V̇O(2max). Differences between heart rates and plasma epinephrine concentrations after, compared with before, training were not statistically significant. These results provide evidence that the NE response to exercise is dependent on the absolute as well as the relative intensity of the exercise.