EFFECT OF INCREASED CENTRAL BLOOD-VOLUME WITH WATER IMMERSION ON PLASMA-CATECHOLAMINES DURING EXERCISE

To examine the influence of an increase in central blood volume with head-out water immersion (WI) on the sympathoadrenal response to graded dynamic exercise, nine healthy men underwent upright leg cycle exercise on land and with WI. Plasma norepinephrine and epinephrine concentrations were used as indexes of overall sympathoadrenal activity. Oxygen consumption (V̇O2), heart rate, systolic blood pressure, and plasma concentrations of norepinephrine, epinephrine, and lactate were determined at work loads corresponding to ~40, 60, 80, and 100% peak V̇O2. Peak V̇O2 did not differ on land and with WI. Plasma norepinephrine concentration was reduced (P < 0.05) at 80 and 100% peak V̇O2 with WI and on land, respectively. Plasma epinephrine and lactate concentrations were similar on land and with WI at the three submaximal work stages, but both were reduced (P < 0.05) at peak exertion with WI. Heart rate was lower (P < 0.05) at the three highest work intensities with WI. These results suggest that the central shift in blood volume with WI reduces the sympathoadrenal response to high-intensity dynamic exercise.