Gait selection in the ostrich: mechanical and metabolic characteristics of walking and running with and without an aerial phase

Abstract

It has been argued that minimization of metabolic-energy costs is a primary determinant of gait selection in terrestrial animals. This view is based predominantly on data from humans and horses, which have been shown to choose the most economical gait (walking, running, galloping) for any given speed. It is not certain whether a minimization of metabolic costs is associated with the selection of other prevalent forms of terrestrial gaits, such as grounded running (a widespread gait in birds). Using biomechanical and metabolic measurements of four ostriches moving on a treadmill over a range of speeds from 0.8 to 6.7 m s -1 , we reveal here that the selection of walking or grounded running at intermediate speeds also favours a reduction in the metabolic cost of locomotion. This gait transition is characterized by a shift in locomotor kinetics from an inverted-pendulum gait to a bouncing gait that lacks an aerial phase. By contrast, when the ostrich adopts an aerial-running gait at faster speeds, there are no abrupt transitions in mechanical parameters or in the metabolic cost of locomotion. These data suggest a continuum between grounded and aerial running, indicating that they belong to the same locomotor paradigm.

Phalangeal joints kinematics during Ostrich (Struthio Camelus) locomotion

“…Previous study revealed that ostriches use an inverted pendulum gait at slow locomotion (Rubenson et al, 2004). The out-of-phase pattern in the fluctuations of the potential and kinetic energies allows for a high percentage of mechanical energy recovery at slow speeds, which are typical of walking in bipedal species (Cavagna et al 1976(Cavagna et al , 1977Heglund et al 1982;Muir et al 1996).…”

“…The out-of-phase pattern in the fluctuations of the potential and kinetic energies allows for a high percentage of mechanical energy recovery at slow speeds, which are typical of walking in bipedal species (Cavagna et al 1976(Cavagna et al , 1977Heglund et al 1982;Muir et al 1996). Whereas, at fast locomotion (including grounded running and aerial running), ostriches tend to use a bouncing gait by using the legs as a springy mechanism to store and regain energy characterized by a marked reduction in the phase difference between the potential and kinetic energies (Rubenson et al, 2004). The distinct toe joint motions at slow and fast locomotion observed in this study are probably the direct result of the selective use of those two distinct energy strategies at different speed ranges.…”

Neither season nor sex affects the cost of terrestrial locomotion in a circumpolar diving duck: the common eider (Somateria mollissima)

“…In aerial running gaits (DF B0.5), each stride has a phase with both feet off the ground, and these energies cycle in phase. An intermediate gait, grounded-running, is also utilised by some birds, which has no aerial phase but has in phase energy cycling characteristic of aerial running (Gatesy and Biewener 1991;Rubenson et al 2004;Hancock et al 2007;Usherwood et al 2008;Nudds et al 2011). During terrestrial locomotion, a bird's rate of energy metabolism, the cost of locomotion, increases as a function of speed (U) until a morphological (mechanical) or physiological (energetic) constraint is met (Brackenbury and Avery 1980;Roberts et al 1998;Nudds et al 2010).…”

“…During terrestrial locomotion, a bird's rate of energy metabolism, the cost of locomotion, increases as a function of speed (U) until a morphological (mechanical) or physiological (energetic) constraint is met (Brackenbury and Avery 1980;Roberts et al 1998;Nudds et al 2010). This increase is often linear (Pinshow et al 1977;Bamford and Maloiy 1980;Taylor et al 1982;Brackenbury and Elsayed 1985;Roberts et al 1998;White et al 2008); however, nonlinearity within and between gaits is also common (Rubenson et al 2004(Rubenson et al , 2007Watson et al 2011;Nudds et al 2011). Elevated energy metabolism at faster U correlates with shorter periods of foot-ground contact, which require higher rates of force production by muscle fibres (Kram and Taylor 1990;Roberts et al 1998).…”

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“…In 75 addition, it was also reported that they are capable of cutting maneuvers with minimal 76 changes of their leg kinematics and joint torques (Jindrich et al, 2007). Some studies showed 77 that ostriches are highly adapted to very economic locomotion from slow walking to fast 78 running (Rubenson et al, 2004(Rubenson et al, , 2010.…”