Prolonged physical training in marathon runners was associated with resting bradycardia, high QRS voltage, enlarged heart size, and a decrease in transverse heart diameter immediately after running.
Observational
What are the electrocardiographic and structural cardiovascular adaptations to prolonged physical effort in trained marathon runners?
Marathon runners exhibit specific resting ECG changes and cardiomegaly, with an acute decrease in cardiac transverse diameter immediately following a 26-mile run.
Studies of the cardiovascular system were made among 26-mile marathon runners after at least five years of physical training. Studies made with the subjects at rest showed an electrocardiogram characterized by a vertical or semivertical electrocardiographic position of the heart in the chest, bradycardia, high voltage of the QRS complexes and high T and U waves. T waves which were low with respect to the height of the R waves were not encountered. Etiologically the heart was enlarged. Immediately after running 26 miles the transverse diameter of the heart was decreased considerably.
BECKNER et al. (1954) conducted an observational in Marathon runners. Prolonged physical effort (marathon running) was evaluated on Cardiovascular adaptations (electrocardiogram and heart size). Prolonged physical training in marathon runners was associated with resting bradycardia, high QRS voltage, enlarged heart size, and a decrease in transverse heart diameter immediately after running.