Abstract
Changes in the heart rate produced by different degrees of activity have been used as a basis in many of the tests of physical efficiency. If the changes in heart rate are not directly proportional to the amount of exercise performed, then tests of physical efficiency based on this principle are not reliable.
Data obtained from 6 typical cases of a group of 75 which have been examined are presented to show the frequency response of the heart to exercise of graded intensities.
The frequency responses of the heart are based on the pulse-ratio. This is determined by dividing the pulse for 2 minutes after a known amount of exercise by the normal sitting pulse for one minute.
The exercise consists of mounting a stool 13 inches high a definite number of times in one minute. Suppose, for example, that after mounting the stool 18 times in one minute the resulting pulserate for 2 minutes is 135. Assuming the normal pulse to be 60, then 18 steps of the exercise produce a pulse-ratio of 2.25.
If the response of the heart as indicated by the pulse-ratio is directly proportional to the amount of exercise performed, then the curve which results from plotting a number of pulse-ratios of an individual against the amount of work done to produce them, is a straight line. The results of such an experiment involving 6 subjects are shown in Fig. 1. In each case, 18 steps is the initial exercise and 40 steps the most strenuous.
If, as is the case with one of the subjects, 18 steps per minute produce a pulse-ratio of 2.17 and 40 steps give 2.63, then by the graphic method, 25 steps should produce a pulse-ratio of 2.33, 30 steps 2.43 and 35 steps 2.53.
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