The slowing pulse: a history of research on training-induced resting bradycardia.

Training-induced resting bradycardia is characteristic of endurance athletes, but it also often occurs in less trained, physically active people. It is commonly believed that slowing of the heart rate is a positive sign of systemic adaptation to physical training, but severe bradycardia phenomenon (below 40 beats per minute) could be a matter of concern for athletes' health. In this review, we present the fascinating history of research into this one of the most fundamental adaptive responses of the cardiovascular system to exercise training, which teaches us an important scientific truth - that nothing that has not been questioned has truly been proven. In the context of training-induced resting bradycardia, this refers to many aspects of the phenomenon, from its name and meaning to its physiological mechanisms.