Viewpoint: Is the resting bradycardia in athletes the result of remodeling of the sinoatrial node rather than high vagal tone?

IT IS WELL KNOWN THAT ATHLETES have a low resting heart rate, i.e., a resting bradycardia and heart rates below 30 beats/min have been reported (7). For example, Wikipedia states that the Tour de France cyclist, Miguel Indurain, had a resting heart rate of 28 beats/min when race fit. The resting bradycardia in athletes is most often attributed to high vagal tone, i.e., high parasympathetic nerve activity (e.g., Ref. 1). However, over the years doubt about this explanation has been expressed (e.g., Ref. 26). Here we take a critical look at the two lines of evidence said to favor the high vagal tone hypothesis: 1) little or no change in the intrinsic heart rate in athletes and 2) an increase in heart rate variability in athletes. Effect of training on intrinsic heart rate in humans. Jose and Taylor (9) investigated the effect of autonomic blockade in conscious human subjects and concluded that injection of 0.