112 MUSCULAR WORK 
continuously measured by a combination of weights and springs, determined 
the efficiency of a number of Arabs in Algeria. The net efficiency varied from 
27 to 38 per cent, with an average of not far from 32.5 per cent, while the 
gross efficiency varied from 3.2 to 5.1 per cent, with an average of 4.5 per 
cent, these values being calculated from the ration eaten by the subjects. 
Amar also computed the net efficiency from the consumption of oxygen as 
measured by means of the Tissot apparatus, finding an average net efficiency 
of 27 per cent instead of the 32.5 per cent found when computed from the 
food intake. When the subject performed 13,748 kilogrammeters per hour 
for 4 consecutive hours, Amar computed the net efficiency from the oxygen 
consumption to be 29.33 per cent for the first hour, 31.23 per cent for the sec- 
ond, 33.81 for the third, and 35.03 for the fourth hour. Other experiments 
gave a similar increase in the efficiency as the work progressed. Of particular 
interest in connection with our research is his study of the effect upon the 
efficiency of the rate of speed. With 70 revolutions of the pedal he found 
with one subject 25.1 per cent, with 80 revolutions 26.7 per cent, with 90 
revolutions 28.4 per cent, while with another subject with 90 revolutions he 
found 30.6 per cent, and with 100 revolutions 25.8 per cent, indicating approx- 
imately an optimum speed of about 90 revolutions of the pedal per minute. 
Considering the conditions under which Amar worked and the difficulties in- 
cidental to an inadequately equipped laboratory, these results are of special 
interest; yet, as pointed out by Lefevre, the values must be taken with consid- 
erable reserve. 
THE UNIT OF EFFICIENCY. 
Gross and Net Efficiency. 
An examination of the earlier literature on the efficiency of the body 
shows that a large number of units of efficiency have been used by various 
writers. If the total energy output for the day is made the base-line, and the 
actual amount of energy transformed into external muscular work taken as 
the numerator, the percentage of efficiency can be obtained by the formula 
— - — , in which a represents the external work performed in calories and 
b 
b the total energy output in calories. This unit, which may be called the 
"gross efficiency," the "crude efficiency," or the "industrial efficiency," 
is naturally largely affected by the amount of work performed during the 
day and the number of hours in which work is done, since at least half of the 
day is usually spent in rest, during which time there is energy output but 
unaccompanied by effective external work. For computation of the energy 
output of a gang of laborers or artisans in a mill and for the provisioning of an 
army or navy under severe stress of muscular work, the gross efficiency is of 
particular value, but in physiological experiments per se it indicates but little 
of the potentialities of the human body for severe muscular work, and gives 
no conception of the possible efficiency of the human body as a machine. 
To find this latter, it is obvious, to say the least, that the energy given off 
when the subject is at rest and not performing muscular work should be 
deducted from the total daily quota. Further than that, it can readily be 
assumed that a deduction should likewise be made of the energy required for 
Letevre, Chaleur animate et bioenergStique, Paris, 1911, p. 212. 
