Comparison of diving bradycardia and maximal aerobic power.

It has previously been suggested that diving bradycardia might be more pronounced in physically trained subjects than in unconditioned ones. Therefore, the cardiac responses to apneic face immersion in water of 25 +/- 1 degree C during rest and exercise in 24 males and females, ranging in age from 21-37 years, were compared to the subjects' levels of physical fitness, as estimated by maximal aerobic power. These values ranged from 46-74 ml.kg-1.min-1. The diving bradycardia was greatly intensified when the face immersion was superimposed on a state of apneic exercise. However, a correlation of the individuals' maximal aerobic power and the mean degree of bradycardia displayed during various maneuvers of apneic face immersion did not approach statistical significance. It is concluded that there exists no relationship between bradycardia and physical fitness, as judged from maximal aerobic power.