Relative roles of the sympathetic and parasympathetic systems in the 4-s exercise test

To evaluate the relative influence of the two branches of the autonomic nervous system on the 4-s exercise test which measures heart rate acceleration at the onset of exercise, 6 healthy male subjects performed the 4-s test under sympathetic blockade with propranolol, parasympathetic blockade with atropine and dual blockade. The magnitude of the 4-s test results (means +/- SD) was significantly different only between the conditions with and without atropine (1.04 +/- 0.03 vs 1.53 +/- 0.33, respectively), with no differences between the control (1.60 +/- 0.25) and the test under sympathetic blockade (1.51 +/- 0.33). These results support the conclusion that the 4-s exercise test is a specific method for the evaluation of parasympathetic activity.