Exercise causes major changes in the functioning of the
cardiovascular system and its mechanisms of autonomic
adjustment.53,54 In this study, a reduction in heart rate variability indexes occurred following moderate aerobic exercise, characterized by the predominance of sympathetic
over parasympathetic activity in both groups, with a more
pronounced response in nonsmokers. Alonso et al53 analyzed heart rate variability in adult subjects submitted to
an exercise test on a stationary bicycle and also found a
reduction in heart rate variability. This decrease is suggested to be largely dependent on vagal withdrawal.