Reproducibility of the catecholamine response to serial exercise testing in normals

Plasma norepinephrine (NE) and epinephrine (E) increase with exercise but the reproducibility of their response to short-term serial exercise testing has not been established. Therefore, NE and E were measured at rest, 6 minutes, peak exercise, and 5 minutes postexercise in 10 normal subjects undergoing three identical exercise tolerance tests within 4-13 days. Norepinephrine and E were also measured in tests 2 and 3 at the time equivalent to the peak exercise duration in test 1 (peak--equivalent). Exercise duration increased slightly from test 1 (15.6 +/- 0.7 min) to test 2 (16.5 +/- 0.5 min; p = 0.07) but no further on test 3 (16.2 +/- 0.9 min). Norepinephrine and E did not differ across the three tests at rest, 6 minutes, peak test or posttest, but a significant decrease in both NE and E was seen at peak-equivalent by test 3 (p less than 0.05). Heart rate decreased across the three tests at 3, 6, 9, and 12 minutes (p less than 0.02 for each) and peak equivalent (p less than 0.005) but was unchanged at rest, peak exercise and postexercise. Thus, plasma catecholamines and heart rate decrease at high levels of exercise with repeated, short-term exercise testing, possibly due to familiarity with the protocol. These results suggest that control groups are important when measuring the effects of short-term pharmacologic intervention by serial exercise tests.