Tetrapod Walking and Running


Animals with four limbs that move about in the terrestrial environment use a variety of different gaits. The style of animal locomotion is strongly dependent on body form and on the speed of travel.

Keywords: gait; locomotion; speed; stability; mobility

Figure 1.

Bipedal human walking. Footprints show step and stride lengths. Lower panel is a gait diagram with horizontal lines representing the time when each foot is on the floor. LF, left foot; RF, right foot, a, double‐support phase; b, single‐support phase; c, aerial plane. Note that the x axis is relative time; the actual time taken to complete a running stride is less than that for a walking stride.

Figure 2.

Graph of relative stride length (λ, stride length; h, hip height) plotted against ‘relative speed’ (u, speed; g, gravitational acceleration) for walking and running humans and horses, and half‐bounding bandicoots (*).

Figure 3.

Gait diagrams for commonly used quadrupedal and bipedal gaits. LH, left hind foot; LF, left fore foot; RF, right fore foot; RH, right hind foot; R, right foot; L, left foot.

Figure 4.

Stiff‐legged walking model showing the arc travelled by the centre of mass (COM). For the COM to travel at speed u in the arc of a circle of radius h, there must be an acceleration u2/h towards the centre of the circle. Therefore, maximum walking speed is approximated by the equation: umax = √gh, where g is gravitational acceleration. Potential and kinetic energies (PE and KE) associated with the COM oscillate out of phase of each other during walking.

Figure 5.

(a) Diagram of a hindlimb of a kangaroo indicating the ground reaction force (GRF) and the tension (T) in the calf muscles, required to balance this force. R and r are the moment arms of these two forces about the ankle joint and r/R is the effective mechanical advantage. (b) Graph indicating how the effective mechanical advantage (EMA) increases with body size as animals adopt more upright limb postures. Hopping kangaroos are an exception to this rule.

Figure 6.

Lines connecting the three supporting feet produce a triangle of support. If the centre of mass (•) falls within this area then the animal is in balance and is stable. Arrows indicate which foot is being lifted and moved forwards in this walking gait.

Figure 7.

Graph showing how maximum running speed varies with body mass. The solid line represents the mean performance for placental mammals over the whole size range, but note that there is a large degree of scatter of data (not shown) about this line. Open triangle, porcupine; filled square, cheetah; filled triangles, kangaroos and wallabies.

Figure 8.

Graphs of how stride frequency varies (a) as an individual animal increases speed (W, walk; T, trot; G, gallop; B, bound) and (b) as a function of body mass at physiologically equivalent speeds (i.e. the trot–gallop transition).

Figure 9.

Tracings from a video sequence of a kangaroo using a bipedal hop. Kinetic and potential energies of the body (1, 2) are temporarily converted to strain energy in tendons (3, 4) and are returned to the body during elastic recoil (5–7), helping accelerate the body forwards and upwards.

Figure 10.

Mass‐specific oxygen (= energy) consumption as a function of speed. Data are derived from treadmill studies. Dotted lines indicate the predicted curves for placental mammals of the masses indicated. Solid lines show empirical data for macropodid marsupials, with the 5‐kg and 18‐kg hopping animals uncoupling the cost of locomotion from speed.


Further Reading

Alexander RMcN and Hayes G (1983) The hopping gaits of crows (Corvidae) and other bipeds. Journal of Zoology, London 200: 205–213.

Baudinette RV (1994) Locomotion in macropodoid marsupials: gaits, energetics and heat balance. Australian Journal of Zoology 42: 103–123.

Baudinette RV, Snyder GK and Frappell PB (1992) Energetic cost of locomotion in the tammar wallaby. American Journal of Physiology 262: R771–R778.

Bennett MB and Taylor GC (1995) Scaling of elastic strain energy in kangaroos and the benefits of being big. Nature 378: 56–59.

Biewener AA (1990) Biomechanics of mammalian terrestrial locomotion. Science 250: 1097–1103.

Biewener AA and Baudinette RV (1995) In vivo muscle force and elastic energy storage during steady‐speed hopping of tammar wallabies (Macropus eugenii). Journal of Experimental Biology 198: 1829–1841.

Biewener AA and Blickhan R (1988) Kangaroo rat locomotion: design for elastic storage or acceleration? Journal of Experimental Biology 140: 243–255.

Cavagna GA, Heglund NC and Taylor CR (1977) Mechanical work in terrestrial locomotion: two basic mechanisms for minimizing energy expenditure. American Journal of Physiology 233: R243–R261.

Garland T Jr, Geiser F and Baudinette RV (1988) Comparative locomotor performance of marsupial and placental mammals. Journal of Zoology, London 215: 505–522.

Heglund NC and Taylor CR (1982) Energetics and mechanics of terrestrial locomotion. Journal of Experimental Biology 138: 301–318.

Ker RF, Alexander RMcN and Bennett MB (1988) Why are mammalian tendons so thick? Journal of Zoology, London 216: 309–324.

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Bennett, Michael B(Apr 2001) Tetrapod Walking and Running. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001867]