THE EFFECT OF EXERCISE ON THE ELECTROCARDIOGRAM IN HEALTHY SUBJECTS

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Abstract
The exercise ecg was recorded in 67 healthy subjects. The exercise was strenuous, but it was always commensurate with the subject s ability to carry it out to the stage of breathlessness or fatigue in none did it produce chest pain. A resting ecg was first recorded, followed by 3 tracings at intervals of 2, 4, and 10 minutes after the exercise. Attention was paid to changes in the P wave, P-R interval, P-Q segment, QRS complex, S-T segment, T wave, T-U segment, and the U wave, together with the appearance of an arrhythmia. The investigation was carried out with a prerequisite knowledge of the lesser ecg changes identified with coronary arterial disease, and these were deliberately sought for in the tracings recorded after exercise. With the exception of lead III, which is regarded as an unreliable lead in the exercise test, the undermentioned changes were not met with in any of the healthy subjects in this series. Thus, provided the R wave was not tall (exceeding 20 mm) the point J was never depressed more than 1 mm below the P-Q segment. The S-T segment never showed a plane or sagging configuration: a plane depression was taken as being present if the S-T segment measured from the end of the S wave to the beginning of the T wave remained flat for a period of 0.1 second. A previously upright T wave never became flat or inverted, the T-U segment was never depressed below the P-Q segment, the U wave never became inverted, and the R wave in lead CR4 never decreased to below 60% of its voltage at rest.