198 METABOLISM DURING WALKING. 



ing, and that the excess energy expended for the grade walking was the 

 energy required to lift the body to a vertical elevation, this elevation 

 being computed from the grade of the treadmill and the linear dis- 

 tance walked at this grade; also that the energy expended for the 

 horizontal component of this linear distance was the same per meter 

 as that determined in the horizontal-walking experiments. Still 

 another assumption is made, namely, that during grade walking there 

 is a certain amount of step-lift, which constitutes a varying amount of 

 work to be added to the work of grade elevation. An effort was made 

 to measure this step-lift and to compute the work which it represented 

 and the energy which it required. It is necessary to consider, there- 

 fore, (1) the work due to the grade of the treadmill, which is referred to 

 as the work of grade-lift; (2) the work due to the heel-and-toe action, 

 i. e., the step-lift; and (3) the sum of these two, which constitutes the 

 work of ascent. As was the case in the horizontal- walking experiments, 

 the measured value of the step-lift is of somewhat doubtful dependa- 

 bility; this in turn affects the total amount of work, the so-called work 

 of ascent. The measure of the work due to grade-lift is, however, 

 believed to be accurate. It will therefore be considered more fully 

 than the other factors, and has been used as the basis of the curves pre- 

 sented in this section. 



The method by which the grade-lift was measured and the computa- 

 tion of the horizontal component of the distance walked have been 

 explained on page 29. (See also fig. 6.) With the low grades this 

 latter value, shown in column d of tables 52 to 55, differs but little 

 from the total distance walked. 



The values used for the standing requirement, which have been de- 

 ducted from the total energy to find the energy requirement for walk- 

 ing, are generally the average values for a period of days, although the 

 average found for that particular day has been used in many instances. 

 The values employed are, in all cases, indicated by footnotes in the 

 tables. In determining the energy to be deducted for the horizontal 

 component, use has been made of the increment per horizontal kilo- 

 grammeter, if found for the day of experiment, and, if not, an average 

 value was employed. When any wide deviation appeared in the values 

 for a subject during the period of study, as was the case with E. D. B., 

 the average value, if employed, is that which in our judgment more 

 nearly represents the average increment at the time of the grade- 

 walking experiments. 



