J. Physiol. (I957) I38, I65-I7I. McCance (1955) added figures for marching. With few exceptions these observations

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1 165 J. Physiol. (I957) I38, I65-I7I THE EXPENDITURE OF ENERGY BY MEN AND WOMEN WALKING BY J. BOOYENS AND W. R. KEATINGE From the Medical Research Council Department of Experimental Medicine, University of Cambridge (Received 21 March 1957) Benedict & Murschhauser (1915) and Passmore & Durnin (1955) collected together and summarized the main observations made on the expenditure of energy when walking at different speeds. Edholm, Fletcher, Widdowson & McCance (1955) added figures for marching. With few exceptions these observations were all made on men. Mahadeva, Passmore & Woolf (1953) found no sex difference in the expenditure of energy of persons walking at 3 m.p.h. on an indoor track. In observations on two women and four men walking at m.p.h., Booyens & McCance (1957) noticed that the women expended less energy than the men. Although there are more women than men in the population, little is known about the energy normally expended by women when they are walking. The expenditure of energy of ten men and ten women have therefore been measured while they were walking in order to find out (1) the range of individual variation, (2) whether there is a sex difference. METHODS The age, height and weight of the subjects and also the ratio between their height and the length of their legs are given in Table 1. Leg lengths were taken as the vertical distance from the greater trochanter to the floor, measured without shoes. The experiments were conducted over a straight outdoor level track 300 yards long. The subjects, wearing flat-heeled shoes, walked along it for 50 yards before their expired air was collected. This was then collected as they walked over the remaining 250 yards and back again. It is believed that these measurements of expenditures of energy will be within 5% of steady-state figures; the two sex groups will be comparable in this respect. Single measurements of gross expenditure of energy and of length and frequency of stride were made on each subject while walking at two rates: (1) a leisurely one, and (2) 'to catch a bus'. Each speed was nearly the same within the group except for subject 2. Her leisurely walking speed resembled the fast walking of the other subjects, and she was consequently asked to walk more slowly, instead of faster, during the second measurement, so that her result could be compared with those of the others. Expired air was collected in Douglas bags (Douglas & Priestley, 1948). A conventional mouthpiece and valve holder with inspiratory and expiratory valves and two lengths of standard corrugated tubing were used in each measurement. The subjects wore the mouthpiece for 2-3 min 11 PHYSIO. CXXXVIII

2 166 J. BOO YENS AND W. R. KEATINGE before they began walking. The valve holder and mouthpiece were held in the most comfortable position by the subjects while they were walking, so they were able to swing only one arm. The Douglas bags were carried by the observers and in no case were over-filled by the end of the collection. For each measurement each subject walked over the course at as constant a speed as possible. The time taken by each of the subjects to cover the course was measured with a stopwatch, and the number of strides taken was counted, so that speed and the length and frequency of the stride could be calculated for each subject at each of the two rates. Samples of expired air were analysed by means of the Hartmann-Braun analyser which was calibrated against a Haldane apparatus (Haldane & Graham, 1935) and the volume of expired air was measured on a calibrated, dry gas-meter. Calorie expenditures were calculated from the tables of Cathcart & Cuthbertson (1931). TABLE 1. The age, height and weight of the subjects and their height/length of leg ratios Women Men Height Height Age Height Weight length Age Height Weight length Subject (yr) (cm) (kg) of leg Subject (yr) (cm) (kg) of leg J. B W.R.K Mean The subjects did not all walk at exactly the same speed. The average speeds were 5-44 and 6-48 km/hr for women, and 5-52 and 6-52 km/hr for men. It has been shown that expenditure of energy increases in proportion to walking speed between 3-22 and 6-44 km/hr (Passmore & Durnin 1955), and is also closely related to body weight (Mahadeva et al. 1953). It was shown that both the length and frequency of stride increase proportionally with speed of walking (Scholtz ) (Figs. 1, 2), and in order to facilitate a general comparison, figures of expenditure of energy and of frequency and length of stride have been corrected by extrapolation (if necessary) to speeds of 5-47 and 6-44 km/hr (3-4 and 4 m.p.h.). In making these calculations the relationships have been assumed to be linear, in conformity with the results given in Figs. 1, 2. The error involved in doing this can only have been small. RESULTS Tables 2 and 3 give the expenditure of energy and length and frequency of stride corrected to 5-47 and 6-44 km/hr, together with their mean and S.D., for women and men. Walking at 5-47 km/hr women expended significantly less energy than men per unit of body weight, they took significantly more strides per minute, and also significantly shorter strides than men. (P < 0-05 expenditure of energy, P<0-001 for both frequency and length of stride.) When the subjects walked at 6-44 km/hr the difference in expenditure of energy between the sexes was even more significant (P <0-01). The over-all difference between women and men in expenditure of energy, therefore, increased with speed. Walking at 5-47 km/hr women expended on the average 0-44 kcal/kg/hr less than men, whereas this difference was 0-74 kcal/kg/hr

3 ENERGY EXPENDITURE DURING WALKING 167 when walking at 6*44 km/hr. These results confirmed the observations of Booyens & McCance (1957) and showed the difference was highly significant. Moreover, this difference is associated with a significantly shorter length of stride in women. In increasing their speed of walking women increased their average frequency of stride from to 141*1 strides/min, and their average length of stride from 72*2 to 76-2 cm. The corresponding figures for men were and strides/min and 85-7 and 93*3 cm, so that in putting up their speed women increased the frequency of their stride more and its length less than did the men. This is also shown in Figs. 1 and 2 which illustrate the way in which subject 8 (a woman) and J. B. varied their frequency and length of stride when called upon to walk at speeds between 3*22 and 8-85 km/hr. At a walking TABLE 2. Subject Mean S.D. TABLE 3. of energy and frequency and length of stride of women walking on the level Figures corrected to 5-47 and 6.44 km/hr. of energy (kcal/kg/hr) * *48 4* * *4 Walking 5*47 km/hr, s \~~~ Frequency of stride/min *3 129*4 124* *9 127* * of stride (cm) * '5 73*1 72* Walking 6*44 km/hr of energy Frequency of stride (kcal/kg/hr) of stride/min (cm) *1 5* * *8 5* *8 4*76 145' X76 143X '40 132* * * * *3 6*7 3*8 of energy and frequency and length of stride of men walking on the level Figures corrected to 5-47 and 6-44 km/hr. Walking 5*47 km/hr Walking 6-44 km/hr of energy Frequency of stride Subject (kcal/kg/hr) of stride/min (cm) 11 4o20 104* *4 15 4* J.B. 4' W. R. K *9 19 4* * Mean S.D. 0* *0 of energy Frequency of stride (kcal/kg/hr) of stride/min (cm) 5* '2 5* * * *0 6*88 114*6 93*6 5* '

4 168 J. BOOYENS AND W. R. KEATINGE 105i- x0x E -o 0 -c. 4) I-J oo X 'X 01: D-<: 0 O 90g X,- Fig. 1. LA JV I 3 I Speed of walking (km/hr) The effect of varying the speed of walking upon the length of stride taken by a woman (subject 8) O---O, and a man (J.B.), x--- x. I I a C -E 130 -o 90 4-, 4) 4) 90 /O / -xx,x~~~~~~~~~4 ox X e Fig. 2. I I I Speed of walking (km/hr) The effect of varying the speed of walking upon the number of strides taken per minute by a woman and a man: conventions as in Fig. 1.

5 ENERGY EXPENDITURE DURING WALKING 169 speed of 4-83 km/hr subject 8 took about 8 strides/min more than J. B., and at 8*05 km/hr took about 20 strides/min more than J. B. The latter's length of stride at 4-83 km/hr was about 6 cm greater than that of subject 8, and at 8-05 km/hr the difference was increased to nearly 13 cm. The ratios of height to length of leg of the subjects are given in Table 1. These ratios varied very little between individuals and the mean value for men, 1F88, was almost identical with that for women, 1F91. TABLE 4. The ratio between the lengths of subjects' strides and the lengths of their legs Women Men of stride of leg of stride of leg Subject 5-47 km/hr 6*44 km/hr Subject 5*47 km/hr 6-44 km/hr * * * X * * * *96 J.B. 1O *86 W. R.K. 0* *02 9 0* *81 0* *82 0* Mean Table 4 gives the ratio between the lengths of the subjects' strides and of their legs at speeds of 5*47 and 6-44 km/hr. This ratio was 0-91 for men and 0-86 for women walking at 5-47 km/hr and 1.00 for men and 0-91 for women walking at 6-44 km/hr. The women, therefore, took shorter strides in proportion to the lengths of their legs at both speeds and the difference between the sexes was more marked at the higher speed. DISCUSSION It is a familiar observation that women walk with shorter strides than men. It was found by Derry (1909) that the acetabular fossae of women 'look more forward' than do those of men. Buchanan (1925) considered that this, and possibly shorter iliofemoral ligaments, restricted extension in the hip joints of women and accounted for their characteristic gait. In conformity with this the women in this investigation took shorter steps in relation to the length of their legs than did the men, although none wore skirts tight enough to restrict their stride. Moreover, this difference in length of stride was associated with a lower expenditure of energy by the women. The difference between the sexes in both length of stride and expenditure of energy was greater at 6-44 km/hr than at 5-47 km/hr. Benedict & Murschhauser (1915) and Steindler (1935) showed that the longer the stride, the nearer the pelvis falls to the walking surface. Thus, the work performed in the vertical plane was increased when the

6 170 J. BOO YENS AND W. R. KEATINGE stride was lengthened. It seems likely, therefore, that the lower expenditure of energy of the women was due to the smaller amount of work they performed in lifting their bodies vertically. Women expended less energy than men at speeds of 5-47 and 6-44 km/hr. At higher and lower speeds they may expend as much or more than men. Thus, Mahadeva et al. (1953) found no difference in expenditure of energy per unit body weight between men and women walking at 3 m.p.h. (4x83 km/hr). This can be accounted for by the fact that the difference in length of stride between the sexes is small at slow speeds (Figs. 1, 2) and there is, therefore, little difference in the muscular effort of walking at slow speeds. Since these same authors found that men and women performing a standardized stepping exercise expended the same amount of energy per unit body weight, it is unlikely that differences in energy requirements between men and women walking can be accounted for by a sex difference in muscular efficiency. Individual differences in energy requirements Within each sex there was a considerable variation in the expenditure of energy by individuals walking at the same speed. These variations were of the same order of magnitude as those found by Mahadeva et al. (1953). Thus, subjects 2 and 6, the women who took respectively the longest and shortest strides; and W. R. K. and subject 19, the men who took respectively the longest and shortest strides, all expended energy at close to the average rate for their sex. This lack of correlation between individual expenditure of energy and length of stride was present at both 5*47 and 6-44 km/hr. Muscular training and efficiency, the weight of clothes, particularly shoes, and slight differences in posture and rhythm of movement will all affect individual expenditure of energy to a greater or lesser degree. To single out any specific cause appears to be impossible. SUMMARY 1. Measurements of the expenditure of energy, and frequency and length of stride were made on ten men and ten women walking at approximately 5-47 and 6-44 km/hr. It was found that: 2. Women expend significantly less energy per unit body weight than men at both these speeds. 3. Women increased their walking speed mainly by increasing their frequency of stride. 4. The smaller expenditures of energy of women were associated with their relatively short strides, and it is suggested that their lower expenditures were due to the smaller amount of work they perform in lifting the body vertically. 5. Considerable individual variations in expenditure of energy were found within each sex group. These were not correlated with variations in length of stride.

7 ENERGY EXPENDITURE DURING WALKING 171 Our thanks go to the subjects for their co-operation and to Drs E. M. Widdowson, M. Stanier and 0. G. Edholm for criticizing the paper. Professor R. A. McCance first suggested that the investigation might be profitable and has helped us very much as a subject and in the preparation of the paper. This work was supported by financial grants (to J.B.) from the Transvaal and Orange Free State Chamber of Mines and the South African Council for Scientific and Industrial Research. REFERENCES BENEDICT, F. G. & MuascmzAusER, H. (1915). Energy transformations during horizontal walking. Publ. Carneg. Instn, no BooYENs, J. & MCCANCE, R. A. (1957). Individual variations in expenditure of energy. Lancet, 272, Buchanan's Manual of Anatomy (1925), p London: Bailliere, Tindail & Cox. CATHCART, E. P. & CUTHBERTSoN, D. P. (1931). The composition and distribution of the fatty substances of the human subject. J. Physiol. 72, DERRY, D. E. (1909). Note on the innominate bone as a factor in the determination of sex. J. Anat., Lond., 43, DOUGLAS, C. G. & PRIEsTLEY, J. G. (1948). Human Physiology, 3rd ed. pp Oxford: Clarendon Press. EDHOLM, 0. G., FLETCHER, J. G., WIDDowsoN, E. M. & MCCANCE, R. A. (1955). The energy expenditure and food intake of individual men. Brit. J. Nutr. 9, HALDANE, J. S. & GRAHAM, J. I. (1935). Methods of Air Analysis, 4th ed. London: C. Griffin and Co. MAHADEvA, K., PASSMORE, R. &_ WOOLF, B. (1953). Individual variations in the metabolic cost of standardized exercises: The effects of food, age, sex and race. J. Physiol. 121, PAssmoRE, R. & DuIRw, J. V. G. A. (1955). Human energy expenditure. Phy8iol. Rev. 35, SCHOLTZ, G. (1953-4). Die Beziehung zwischen SchrittlInge und Schrittzahl beim naturlichen Gang. Arbeit8physiol. 15, STEINDLER, A. (1935). The Mechanics of Normal and Pathological Locomotion in Man, p London: Bailliere, Tindall and Cox.