154 
MUSCULAR WORK 
rate even during severe muscular work, very closely followed the amount of 
the energy output, an observation that is fully in accord with the values se- 
cured with normal resting subjects which show that the pulse-rate and the 
total metabolism are intimately related. Although innumerable observations 
of the pulse-rate were made in this study, it seems unnecessary to report these 
in detail, and we accordingly give only a few series of pulse-rate observations 
which were made before, during, and after the work with each of the inten- 
sities of muscular work performed. 
The values for 4 experiments in which the subject was producing approxi- 
mately 1.05 calories of external muscular work per minute are indicated by 
the curves in fig. 6. Before the experiments, when the subject was lying 
quietly, the pulse-rate was usually not far from 60 to 64 per minute, but after 
the work began there was a rapid ascent of the pulse-rate until it reached an 
average not far from 125 per minute with this degree of muscular activity. 
Immediately on the cessation of work, which is indicated on the chart by 
arrows, the pulse began to fall, the first observation being invariably many 
beats per minute less, although there was a distinct tendency for the pulse- 
rate after the work to become stationary at a higher level than it was before. 
With an external work production of 1.5 calories per minute, the changes 
in the pulse-rate were even more strikingly marked, as shown by fig. 7. 
Here again with an average rate during rest of approximately 64, there was 
inside of 20 minutes a rise in the pulse-rate to a level of approximately 160 
180 
170 
160 
150 
140 
130 
120 
110 
100 
90 
80 
70 
60 
50 
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 
Fig. 7. — Curves showing the pulse-rate when the external muscular work 
was equivalent to 1.5 calories per minute. 
per minute. With the cessation of work, the pulse fell rapidly, and the first 
values obtained in the rest-period after work were invariably much lower. 
The tendency for the pulse-rate to stop at a much higher level than before 
the experiment is even more clearly shown than in fig. 6, the average level after 
work for these 4 experiments being not far from 83 beats per minute, as com- 
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