PLASMA NOREPINEPHRINE RESPONSES TO CYCLE EXERCISE IN BOYS AND MEN

Previous reports have suggested that plasma norepinephrine levels duri ng exercise, an indicator of sympathetic neurologic activity, may be l ess in children than in adults. This study investigated plasma norepin ephrine values at rest, during two submaximal cycle exercise intensiti es, and at maximal exercise in 11 boys aged 10 to 12 years and 11 men aged 24 to 35 years. Blood specimens were drawn at average submaximal exercise intensities of 58.7% and 73.0% for the boys and 55.3% and 73. 3% VO(2)max for the men. Weight-relative maximal aerobic power was sim ilar in the two groups. No statistically-significant differences were observed in plasma norepinephrine values at rest or during submaximal and maximal exercise between the boys and men. Maximal levels were 119 6 (326 SD) and 1385 (612 SD) pg . ml(-1) for the boys and men, respect ively (p > 0.05). These findings suggest that sympathetic influences d uring maximal and submaximal exercise are independent of biological ma turation.