walking or trotting), the muscular input force required to sustain oscillation of the system is minimal. When animals adopt speeds close to the optimal stride length and frequency for a particular gait type (e.g. Together these findings suggest that, although gait transitions do have energetic benefits, energetic increases are not the primary trigger for gait transitions.Īn alternative approach to understanding gait transitions emerges from a dynamical systems perspective of animal movement. In particular, small-bodied species show a more monotonic decrease (reversed J-shape) in COT when they walk, such that there is no reciprocal increase in COT after the minimum value for walking is reached, and the COT of trotting is near the minimum COT of walking. Finally, gait transitions do not always result in a reduction of energetic expenditure.

Moreover, although some studies suggest that the PTS and EOTS can be concurrent, other research with humans demonstrates that the PTS can occur either before or after the EOTS. later showed that perceived effort is highly variable, but for most participants the highest level of perceived effort occurs after they have already made the transition from a walk to a run. when subjects changed gaits from a walk to a run) their sense of effort decreased by 26.2%, but their actual energy costs increased by around 16%. In the words of Farley & Taylor, ‘It is difficult to imagine how energetic cost could trigger a gait transition as an animal rapidly changes speed.’ Hreljac demonstrated that when human participants rated their perceived exertion at and around their PTS (i.e.

It is unclear what sensorimotor feedback mechanism would indicate to an animal that they could save energy by changing gaits. This energy minimization hypothesis for gait transitions is not without its critics. In many species the EOTS and the PTS are very similar, suggesting that increasing energetic costs might play a role in triggering gait transitions. trotting) is the energetically optimal transition speed (EOTS). walking) intersects the COT curve for another (e.g. The speed at which the COT curve for one gait (e.g. This makes it energetically costly to maintain those gaits, and gait transitions become critical for energy conservation. However, as animals adopt speeds near the peaks of their gait-specific COT curves, energy costs increase rapidly. For the most part, when animals are allowed to move at self-selected paces, they select the most economical speeds within a given gait type and avoid speeds that are more energetically costly. The peaks of the lines are locomotor speeds with a high COT and the valleys are speeds with lower energetic costs.

In an idealized situation (electronic supplementary material, figure S1 a), plots of the energetic cost of transport (COT) per unit distance (J kg −1 m −1) against locomotor speed reveal intersecting curvilinear relationships for different gaits (e.g. The most commonly cited function of gait transitions is to minimize energetic expenditure. While numerous studies have characterized gait transitions from kinematic, kinetic and metabolic perspectives, the mechanism triggering gait transitions remains unclear. For many species, the speeds at which gait transitions occur are highly constrained to what are referred to as preferred transition speeds (PTS). walk, run, trot and gallop)-they perform gait transitions. A general feature of terrestrial locomotion by mammals and birds is that, as they increase speed, they switch between gaits (e.g.

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