MECHANICAL EFFICIENCY OF THE HUMAN BODY 
107 
performed 100,000 kilogrammeters of work during the day, this being equiv- 
alent to 234 calories. Deducting the energy requirement during rest, Rubner 
found that for the 231 calories of external muscular work, the increase in 
energy was 845.3 calories with a sugar diet and 855.6 calories with a protein 
diet. The average net efficiency may readily be computed as follows: 
^34X100 
= 27.5 per cent. In this experiment Rubner's computations of 
850 
the energy requirement were based upon the carbon-dioxide determinations 
alone, no oxygen determinations being made. 
The Gartner ergostat and other forms of ergometer permit a study of the 
work done by the arms only. The work of the legs in walking and climbing 
has been shown by the experiments of the Zuntz school to be more economi- 
cally done than is the work of the arms, and hence it is particularly fortunate 
that the bicycle ergometer has been rapidly developed as an instrument of 
precision. 
The experiments of Leo Zuntz, a in which the metabolism incidental to 
bicycle riding was first studied and an efficiency of 33.33 per cent computed, 
have been more illuminated by the subsequent study of the resistance to be 
overcome by riding a bicycle. 6 In the light of this last study Berg, du 
Bois-Reymond, and Zuntz computed that Zuntz in his first experiments 
showed a net efficiency of 28 per cent. 
Table 104. — Relation of external muscular work to energy katabolized per day, as reported 
by Atwater and Benedict. 
Subject and kind of experiment. 
Dura- 
tion. 
Energy katabolized. 
Efficiency. 
Total. 
Excess in 
work over 
rest ex- 
periments. 
alent of 
muscular 
work. 
Net. 
Gross. 
Subject, E. O.: 
Subject, J. F. S.: 
Average of 4 rest experiments 
Subject, J. C. W.: 
days. 
42 
12 
12 
18 
4 
46 
46 
46 
cola. 
2,279 
3,892 
2,119 
3,559 
2,357 
5,056 
5,332 
5,143 
cols. 
1,613 
1,440 
2,699 
2,975 
2,786 
cols. 
2ii 
233 
529 
601 
546 
p.ct. 
13.3 
16.2 
19.6 
20.2 
19.6 
p.ct. 
5.*5 
'6.6 
10.5 
11.3 
10.6 
Minimum of 14 work experiments .... 
Maximum of 14 work experiments. . . . 
Average of 14 work experiments 
The stationary form of bicycle, i. e., a bicycle with resistance, or a bicycle 
ergometer, was first employed by Atwater and his associates in connection 
with the studies on muscular work conducted at Wesleyan University. 
In the earlier experiments, while the oxygen was not measured, a measure- 
ment was made of the total heat production by placing both ergometer and 
subject inside a large respiration calorimeter. The data secured in these 
experiments thus permit the computation of the efficiency. Unfortunately 
the estimates of the actual amount of external muscular work performed on 
this earlier machine will always be somewhat questionable; on the other hand 
the values for the total heat production as measured by the calorimeter can 
be considered as accurately established. 
a Leo Zuntz, Untersuchungen Qber den Gaswechsel und Energieumsatz des Radfahrers, Berlin, 1899. 
b Berg, du Bois-Reymond, and Leo Zuntz, Archiv f. Anat. u. Physiol., Physiol. Abth., Suppl., 1904, p. 20k 
