One of the best indices of general physical condition is supposed to be the rapidity with which the pulse returns to normal after exercise. In connection with the extensive series of observations carried on at the Y. M. C. A. College by Professors McCurdy and Berry, the investigation of Professor Johnson on the pulse-rate after work on a bicycle ergometer had special significance, since our subjects were for most of the time on reduced diet and a control squad was available for normal data. The men rode a bicycle ergometer,1 at the rate of 80 revolutions per minute for exactly 5 minutes and with a current of 1.35 amperes through the field. Using the data secured in the calibration tests of this ergometer, as published by Benedict and Cady, Professor Johnson has computed that the total amount of work performed by each subject is as follows:

"When the pedal revolution is 80 per minute and the current 1.35 amperes, the heat produced per revolution is 0.0198 large calorie. In 5 minutes there are 400 revolutions, producing 7.92 calories.2 The mechanical equivalent of heat is taken as 427.3 kilogrammeters for each calorie. Multiplying, the result is 3,384 kilogrammeters".

This corresponds to 11.3 kilogrammeters per second, and if converted to foot-pounds, equals 81.6 foot-pounds or about one-seventh horsepower. To give some idea of the approximate amount of work performed in common terms, this would be equivalent to the work done by an individual weighing 163 pounds climbing a 6-inch step every second and attaining an elevation of 150 feet in 5 minutes.

Of special importance, however, is the fact that every subject, in both Squads A and B, performed exactly the same amount of work.

1 Benedict and Cady, Carnegie Inst. Wash. Pub. No. 167, 1912. (See description of ergometer II, p. 6).

2 This amount of external muscular work corresponds to about 1.5 calories, and is thus comparable with the amount of work employed in some earlier experiments. See Benedict and Cathcart, Carnegie Inst. Wash. Pub. No. 187, 1913, p. 154.

Indeed, the exertion prior to and immediately following this work was also exactly the same in all cases. Previous to the riding the subject lay upon a table while the basal1 normal pulse-rate for that day was taken; he then made a few uniform movements in seating himself upon the ergometer; after 5 minutes of riding he immediately lay down upon the table again. The amount of work performed by each subject was therefore exactly the same. This is important in interpreting the differences, not only in the heart rate under the influence of work, but likewise in the return to normal; also the effect of the low diet and resumption of normal diet upon both the total heart rate and on the rate of return to normal. After the subject had returned to the table, the pulse was taken the first 15 seconds of every minute until it reached the normal pulse for the day.

Pulse-Rate Before And After Work On Bicycle Ergometer, 8quad A

It is impracticable to reproduce here all of the many observations obtained by Professor Johnson, these numbering several thousand, but a typical day (November 23) has been selected for illustration, on which all members of Squad A took the test. This day likewise represents the period of approximately minimum lying pulse for the entire squad, as well as the minimum body-weight. The data for November 23 are given in table 103. The first pulse column records the average of at least 3 readings prior to work; the remaining values show the pulse-rate in the first 15 seconds of every minute following the work, and are continued until they reach the level before work. Significant features in these records are, first, the very great increase in pulse-rate due to the work, that is, the heart rate increases very greatly from before work, with the subject in the lying position, to immediately after work, with the subject again in the lying position. The greatest increase in table 103 is shown by Moy whose heart rate prior to work was 41 and in the first minute after work 116. In many other instances the heart rate is doubled. The headings of the columns indicate the minute when the pulse-rate of each subject returned to the rate prior to work. It will be seen that 4 subjects required 18 or more minutes, but that 6 subjects returned to normal in 5 minutes or less.2

In addition to the pulse-rates given for November 23 we have recorded in table 104 the pulse-rates obtained for most of the members of Squad A on one of the last days with reduced diet (January 31,1918) and on four subsequent days with unrestricted diet. In these four days there were pronounced changes in both body-weight and initial pulse-rate.

1 "Basal" for comparison purposes but not minimum, as all values were obtained with food.

2 The fact that in the experiments of Benedict and Cathcart the pulse after work stayed at a higher level is not at variance with these findings, for it should be pointed out that Benedict and Cathcart's subject worked over one hour instead of 5 minutes, and undoubtedly the metabolism and pulse-rate were stimulated many hours after the cessation of work.

Table 103. - Pulse-Rate Before And After Work On Bicycle Ergometer - Squad A, Subjects In Lying Position, With Food. November 23, 1917

1 Average number of minutes taken to return to normal, 10.1.

Table 104. - Comparison Of Pulse-Rates Before And After Work On Bicycle Ergometer With Reduced Diet And With Unrestricted Diet - Squad A

[Subjects in lying position, with food].

1 Unrestricted diet began with breakfast, Feb. 3.

2 Kon showed a pulse-rate of 82 at the 21st minute.

From table 104 several important facts may be observed. In the first place, attention is called to the great increase in pulse-rate due to the work on the ergometer, which is shown by the records for the* first minute after riding. With one or two subjects with low pulse-rate before work like Vea, Pea, and Gul on January 31, the pulse-rate is more than doubled as a result of the work of riding. In a number of cases the pulse-rate is almost doubled, notably with Kon, Gar, Moy, and Pec.