Electrocardiographic study of 20 champion swimmers before and after 110-yard sprint swimming competition.

In order to record the strain of actual competition, 20 healthy young athletes were studied by serial electrocardiograms recorded after swimming races of 110 yards. Blood pressures and electrocardiograms were taken at 3, 6, 9, 12, 15, 20, 25 and 30 minutes after each race. Of the 20 cases studied, 18 showed at least one of the following abnormal findings: (1) The PR interval was prolonged by at least 0.04 second and up to 0.10 second (12 subjects). (2) "True" ST depression (two subjects) or "false" ST depression (six subjects) was seen. (3) A marked loss of T potential (all subjects) or T inversion (eight subjects), which in some had developed as late as the 12-minute reading, was recorded. The causes for these alterations are considered physiological under the conditions of this experiment.