Eur J Appl Physiol (1991) 62:7-10 European Applied Physiology and Occupational Physiology © Springer-Verlag 1991 Energetics of locomotion in African pygmies G. Ferretti 1, G. Atchou 2, B. Grassi 3, C. Marconi 3, and P. Cerretelli 1 i D6partement de PhysiologiC, Centre M6dical Universitaire, Avenue de Champel 9, 1211 Gen~ve 4, Switzerland 2 D6partement des Sciences Physiologiques, Centre Universitaire des Sciences de la Sant~, Yaound~, Cameroon 3 Sezione di Fisiologia, I.T.B.A., Consiglio Nazionale delle Ricerche, Via Ampere 56, 20100 Milano, Italy Accepted July 17, 1990 Summary. The energy cost of walking (Cw). and running (Cr), and the maximal 0 2 consumption (VO2max) were determined in a field study on 17 Pygmies (age 24 years, SD 6; height 160 cm, SD 5; body mass 57.2 kg, SD 4.8) living in the region of Bipindi, Cameroon. The Cw varied from 112 ml. kg-l. km-1, SD 25 [velocity (v), 4 km-h -1] to 143 ml.kg -1 .km -1, SD 16 (v, 7 km.h-l). Optimal walking v was 5km.h-k The Cr was 156ml.kg-l.km -1, SD 14 (v, 10km.h -1) and was constant in the 8-11 kin. h -1 speed range. The l?O2max was 33.7 ml.kg -1 -min -1, i.e. lower than in other Afri- can populations of the same age. The Cr and Cw were lower than in taller Caucasian endurance runners. These findings, which challenge the theory of physical similarity as applied to animal locomotion, may depend either on the mechanics of locomotion which in Pyg- mies may be different from that observed in Cauca- sians, or on a greater mechanical efficiency in Pygmies than in Caucasians. The low Cr values observed enable Pygmies to reach higher running speeds than would be expected on the basis of their VO2m~x. Key words: Energy cost - Ethnic groups - Maximal 02 consumption - Pygmies - Running - Walking Introduction The energy cost of walking (Cw) and running (Cr) per unit body mass and distance (in ml of 02. kg- 1. km- 1) is a ratio of the net (i.e. measured minus resting value) specific oxygen consumption (1702, in ml. min -1. kg -1 of body mass) and the horizontal speed (in km. h- 1 of m. s-1). In Caucasians, Cw and Cr, as well as the corre- sponding mechanical work, are greater for children than for adults at any given speed (Astrand 1952; Ca- vagna et al. 1983; Silverman and Anderson 1972). How- ever, such differences disappear when the speed is ex- Offprint requests to: G. Ferretti pressed relative to the body size, e.g. when the meta- bolic power (I202) is plotted as a function of the Froude number (dimensionless, equal to v2.g-l.1-1, where v is the forward velocity, g the acceleration due to gravity, and I the length of the lower limb from the hip to the ground; see Alexander 1976). This finding indicates that the greater Cw and Cr observed in chil- dren compared to adults depend only on the smaller body size of the former. Pygmies of West Africa constitute a highly homoge- neous ethnic group characterized by a small body size and by an average height 10%-15% lower than that of Caucasians and of surrounding African populations (Dietz et al. 1989; Pennetti et al. 1986). Should their mechanics of locomotion be similar to that of any other known ethnic group, Cw and Cr at any given speed would be greater in Pygmies than in adult Caucasians, as is the case for children. The aim of the present study was to determine on a group of African Pygmies the Cw and Cr in relation to body size. In addition, measurements of maximal 02 uptake (1202max) were carried out in the natural habitat of this population. Methods The experiments were conducted at Bipindi, South Cameroon, in January 1989 (ambient temperature 320-34° C, relative humidity about 90%). Bipindi is situated in tropical forest, 60 km east of Kribi and of the Atlantic coast, in a region highly populated by Pygmies of the Bakola group (Loung 1987). Seventeen male Bakola Pygmies participated in the study. Their habitat is the forest surrounding Bipindi and their living ha- bits are hunting, fishing and harvesting the forest. Some of them have regular contacts with Bantu villagers. One of them, who spoke French, acted as our guide and interpreter. The subjects were chosen randomly at the Pygmies' campsites from young males in apparent good health. Nevertheless, some of them were later found positive for filariosis and for hepatitis A and B. None was forced to participate in the experiments. A modest unsolicited donation in the form of salt and flour was made to the commu- nity. Prior to the measurements, the subjects were instructed about the protocol and carefully familiarized with the techniques to be