Fig. 4.

Effect of exercise training on sinoatrial node recovery time (SNRT) corrected for HR before and after complete autonomic neural blockade. Corrected SNRT significantly increased with increasing atrial stimulus frequency both before and after combined autonomic nervous system (ANS) blockade (propranolol HCl, 1.0 mg/kg + atropine sulfate 50 μg/kg). However, exercise training did not alter the SAN response to rapid atrial pacing; that is, there were no differences between the exercise-trained and sedentary groups. These data suggest that the intrinsic properties of the SAN pacemaker were not altered by exercise. SNRT was corrected for HR using the technique described by Chadda et al. (19).