The series of ECG examination were performed to study the influence of different kinds of exercise on heart of two untrained middle aged healthy male volunteers.
One of them was assigned to run 10 kilometers or so, as fast as he could, once a day for 17 days. The other was assigned to run on a treadmill of three degree gradient for 20 minutes with a speed of 150 meters per minute once a day for 10 years. This volume of exercise was designed at a workload requiring 2/3 of his VO₂max value.
In the former case, frequent supraventricular premature beats with ventricular aberrant conduction occurred on the 21 st day from the beginning of the study. These changes on ECG were complicated with sinus arrhythmia and complete AV block on the 23 rd day. Sinus bradycardia and supraventricular bigeminy with ventricular aberrant conduction were noted on the 44 th day. Supraventricular bigeminies still persisted on the 213 th day, however they disappeared after that.
The latter developed interpolated ventricular premature beats at rest for the first time in the 5 th year from the beginning of the study. These premature beats disappeared during exercise and recurred at rest. In the 8 th year ventricular premature beats became to show bigeminies.
These results suggest that the severe exercise could cause various types of arrhythmia for a long period of time after the cessation of exercise even if the term of exercise would be short. On the other hand, the moderate load of exercise could not cause clinically significant arrhythmias inspite of continuous performance for a long term.