EFFICIENCY IN GRADE WALKING. 249 



EFFICIENCY IN GRADE WALKING. 

 EFFICIENCY IN WORK DUE TO GRADE-LIFT. 



The efficiency with which the work of grade walking was done has 

 been computed from the increment in the heat-output and the kilo- 

 grammeters of work performed due to grade-lift, the value of 426.6 

 kg. m. being used as the mechanical equivalent of 1 calorie. 1 In 

 calculating the percentages, 2.34 gram-calories is taken as the heat 

 equivalent of 1 kg. m. Since the heat values here used are increments 

 above the standing and horizontal- walking requirements, the results 

 represent "net" efficiencies. 2 



A study of these efficiencies in relation to the work performed in 

 grade-lift is of physiological importance. (See column q of tables 52 

 to 55, and column o of table 56.) For A. J. O. and W. K., with a 3.6 

 per cent grade, and E. D. B. with a 5 per cent grade, the efficiencies 

 are all high (approximately 40 per cent) . The amounts of work done 

 on these low grades were 172 kg. m. for A. J. 0., and under 150 kg. m. 

 for W. K. and, in most cases, for E. D. B. This amount of work is 

 equivalent to approximately one-third of a calorie as compared with the 

 total heat measured of 3 to 4 calories, from which total must be de- 

 ducted the standing and horizontal- walking values. An error of 0.1 

 calorie in estimating these values would be a very appreciable amount 

 of the one- third calorie attributable to the work. With these grades 

 the horizontal- walking factor was determined on each day for W. K. 

 and E. D. B. (except for one day in April) and the standing value was 

 the average, with E. D. B., of 23 determinations, with a maximum dif- 

 ference of 0.13 calorie and a maximum deviation from the average of 

 0.07 calorie. The difference between the average standing value of 

 1.10 calories taken for W. K. and the two standing values nearest the 

 date on which he walked with a 3.6 per cent grade differ by only 0.01 

 and 0.05 calorie. These variations are small, and while they might 

 account for the irregularities in the efficiencies for the different days, 

 they would not account for the constant high efficiencies for these low 

 grades. We are inclined to the opinion that the subject walking on a 

 low grade and performing less than 200 kg. m. of work did so at an 

 efficiency in the neighborhood of 40 per cent. With 250 kg. m. of 

 work and upward, the efficiency for all the subjects is seen to approach 

 30 per cent. 



The effect of the speed on the efficiency with which the work was 

 done may be found from table 56, in which the figures indicate a de- 

 creasing efficiency with increasing speed for a definite grade, which 



^rmsby, Principles of animal nutrition, New York, 2d ed., 1906, p. 233. A so-called "best" 

 value of 426.7 is reported in the Smithsonian Physical Tables, Washington, 1920, table 212, p. 197. 

 Our computations were made previous to the publication of this edition by means of the slightly 

 lower figure of 426.6. 



2 We have not considered "gross" efficiency in this discussion. Obviously all the data for its 

 computation are readily found in the several tables. 



