MECHANICAL EFFICIENCY OF THE HUMAN BODY. 
The relationship between the energy consumption and the output of 
work, which has been extensively studied with different machines, is a rela- 
tionship which is likewise of great interest in the study of the mechanical 
efficiency of the human body. The experiments reported in this publication 
were primarily designed to furnish evidence with regard to the relationship 
between the total energy transformation and the external muscular work 
performed, and it is the purpose of this section of the report to discuss the 
experiments from this particular standpoint. 
It may be desirable first to define what is meant by efficiency. Two 
terms are used by writers in this connection, but unfortunately often without 
sharp distinction. In this review of the literature on the subject, the term 
"gross efficiency" is used to designate the value obtained as a result of divid- 
ing the actual heat equivalent of the external effective muscular work by the 
total energy output of the man. This has frequently been designated by 
writers as "gross efficiency," "industrial efficiency," and "crude efficiency." 
When from the total output of the day is deducted the output for a period of 
corresponding length without external muscular work, the result gives the 
increase in the energy output which is caused by the work. Dividing the heat 
equivalent of the external muscular work done by the increase in the energy 
due to the work gives a value which may be designated as the "net efficiency." 
These two base-lines are those most commonly used by writers. In this pub- 
lication other base-lines are considered and designations for these will appear 
in their regular places. 
PREVIOUS STUDIES ON MECHANICAL EFFICIENCY OF THE HUMAN BODY. 
Even the early literature gives evidence which can be used for the com- 
putation of the efficiency of the body as a machine, for in the experiments 
of Lavoisier and Seguin, which we have already cited, we find that for the 
performance of work equivalent to the lifting of 7.343 kilograms to 799 meters, 
i. e., 5,867 kilogrammeters, Lavoisier's subject required an increase in the 
oxygen consumption over and above resting of 36.8 liters. Assuming a 
respiratory quotient of approximately 0.87 (the average of the respiratory 
quotients obtained in over 100 experiments with our subject), the calorific 
equivalent of oxygen would be 4.887 calories, 6 so that 36.8 liters of oxygen 
would correspond to 179.8 calories. The heat equivalent e of 5,867 kilo- 
grammeters would equal 13.8 calories; hence it appears that at the most 
about 7.7 per cent of the oxygen consumed over and above the amount 
consumed during rest was used for mechanical work, and about 4.4 per cent 
of the total amount of oxygen consumed. Lavoisier and Seguin also made 
observations on a man during digestion, and although the experiments are 
not well adapted for computing the efficiency, they are of interest in this con- 
nection. The total amount of oxygen consumed in an hour during work was 
91.2 liters, an increase over resting of 53.6 liters. The subject performed 
6,202 kilogrammeters of work, the calorific equivalent of which would be 14.6 
a The oxygen consumption Per hour, resting, equalled 26.66 liters. & See p. 33 of this report. 
' In this report 1 calorie is considered as equal to 425 kilogrammeters, the value most used by the various 
investigators. 
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