PHYSIOLOGICAL EFFECTS 163 
THE AFTER-EFFECTS OF MUSCULAR WORK. 
The long-continued rapidity of respiration and heart-beat after exercise, 
as, for instance, after running, is familiar evidence that the intense metab- 
olism incidental to active muscular work does not instantly disappear with 
the cessation of the work. One of the earliest observers on this point is 
Vierordt a who has said: "Es ist folglich die korperliche Bewegung von 
sehr grossem und nachhaltendem Einflusse auf die Ausscheidung der Kohlen- 
saure." Later, Edward Smith, 6 in his discussion of the after-effects of work 
on respiration, wrote: "It is evident that whilst there is, during the whole 
interval of rest, an increase in the respiratory changes over that of rest apart 
from this exertion, the great excess due to the exertion disappears after 5 
minutes' rest." 
The first accurate measurements of the increased metabolism following 
muscular work were reported by Speck, c who, recognizing a definite relation- 
ship between pulse and metabolism, states in the report of one of his experi- 
ments that the pulse-rate, after muscular activity sufficient to bring it to 160 
beats per minute, had only dropped to 96 beats per minute in a period of 24 
minutes after the exercise had ceased. In discussing the fact that he always 
found increased carbon-dioxide production and oxygen consumption long 
after the cessation of work, Speck expressed the belief that the increase in 
the carbon dioxide expired cannot be due simply to the increased production 
during the few minutes of work, but that this increase in the formation of 
carbon dioxide must continue throughout the 20 or 25 minutes after work 
in which the greater output is observed. 
In reporting the muscular-work experiments with the respiration chamber 
at Wesleyan University, Middletown, Connecticut, Atwater, Woods, and 
Benedict,** commenting upon the results following a work experiment, state 
that a rest-period of 6 hours was sufficient to bring the elimination of carbon 
dioxide again to the normal, even after a period of hard muscular work in 
which the production of carbon dioxide amounted at times to 500 grams in 
6 hours. An examination of the results shows that the data are not so re- 
corded as to permit this comparison, for the period preceding sleep included 
the whole time between 3 p.m. and 9 p.m., although the work unquestion- 
ably ended about 6 p.m. The first rest-period for comparison would thus be 
the period from 9 p.m. to 3 a.m. whereas the work had actually ceased some 
3 or 4 hours previous. The after-effect of the work would obviously have been 
greater between 6 p.m. and 9 p.m., but this would not be shown by the results 
since the data would be included in the values given for the work-period. 
In subsequent publications from Wesleyan University, the after-effects 
of muscular activity were markedly shown; a summary of these results has 
been prepared and discussed by Benedict and Carpenter.' Computing the 
heat production during sleep from 1 a.m. to 7 a.m. following different con- 
ditions of activity, they find the averages given in table 135. The work per- 
formed consisted of riding one of the various types of the bicycle ergometer 
used in that laboratory, the moderate work ranging from 130 to 280 calories 
° Vierordt, Physiologie des Athmens, Karlsruhe, 1845, p. 100. 
» Smith, Phil. Trans., 1859, 149, p. 711. 
« Speck, Phvsiologie des menschlichen Athmens, Leipsic, 1892, p. 85. A summary is given of earlier papers. 
A Atwater, Woods, and Benedict, U. S. Dept. Agr., Office Exp. Stas., Bui. 44, 1897, p. 52. 
« Benedict and Carpenter, Carnegie Institution of Washington Publication No. 126, 1910, p. 193. 
