Why change gaits? Dynamics of the walk-run transition.

Abstract

Why do humans switch from walking to running at a particular speed? It is proposed that gait transitions behave like nonequilibrium phase transitions between attractors. Experiment 1 examined walking and running on a treadmill while speed was varied. The transition occurred at the equal-energy separatrix between gaits, with predicted shifts in stride length and frequency, a qualitative reorganization in the relative phasing of segments within a leg, a sudden jump in relative phase, enhanced fluctuations in relative phase, and hysteresis. Experiment 2 dissociated speed, frequency, and stride length to show that the transition occurred at a constant speed near the energy separatrix. Results are consistent with a dynamic theory of locomotion in which preferred gaits are characterized by stable phase relationships and minimum energy expenditure, and gait transitions by a loss of stability and the reduction of energetic costs.Motor behavior in humans and animals exhibits two notable features: the presence of stable patterns of coordination and the sudden reorganization that occurs when switching between them. Much research has been directed at describing individual motor patterns such as walking and reaching, but the study of behavioral transitions may reveal principles of the formation of coordinative patterns. Locomotion offers a model system for the study of both, for it is a fundamental, fluent, and complex behavior that is likely to share basic characteristics with other skilled actions. In this article, we examine the shift between walking and running in humans and offer a qualitative dynamic theory of gait transitions.As speed increases, humans and other animals shift from a walking gait to a running gait at a characteristic speed. Why does this occur? A common view is that each gait is orchestrated by a central motor plan, such as a motor program or spinal pattern generator, and that gait transitions simply involve switching between plans (e.g., Shapiro, Zernicke, Gregor, & Diestel, 1981). This view does not offer predictions about the details of behavior at gait transitions. By contrast, we propose that gait transitions are a consequence of the intrinsic dynamics of a complex system, with properties characteristic of bifurcations between attractors. We show that the walk-run (W-R) transition exhibits features of a nonequilibrium phase transition and that it occurs at a speed that tends to reduce energetic costs. This

Inter-limb coordination in swimming: Effect of speed and skill level

“…Although this coordination mode appears to be the most stable and the easiest to perform in bimanual coordination (Kelso, 1984), hand-foot tasks (Jeka, Kelso & Kiemel, 1993;Kelso & Jeka, 1992) and walking-running (Diedrich & Warren, 1995), this arm to leg coordination was ineffective for breaststroke swimming because it entails a freezing of the degrees of freedom (as previously observed on ski-simulator, Vereijken et al, 1992) that superposes contradictory actions: (i) an overlap of arm recovery with leg propulsion (i.e., arms and legs simultaneously extended, Fig. 3) and (ii) an overlap of arm propulsion with leg recovery (i.e., arms and legs simultaneously flexed, Fig.…”

“…Finally, the continuous relative phase (CRP) for a complete cycle was: CRP = Elbow phase angle -Knee phase angle (5) Theoretically, two coordination modes are possible: in-phase (0°) and anti-phase (180°); however, as adopted by Bardy, Oullier, Bootsma, and Stoffregen (2002), Diedrich and Warren (1995), and Seifert, Delignières, Boulesteix, and Chollet (2007), a lag of ± 30° was accepted in this study for the determination of a coordination mode. Therefore, an in-phase mode was assumed to occur for -30° < CRP < 30°, while the anti-phase mode was taken to be between -180° < CRP < -150° and 150° < CRP < 180°.…”

Central pattern generators for bipedal locomotion

“…These authors often focus on either the energetics (for example, see Alexander [2,1] and Minetti [29]) or the biomechanics of the two gaits (for example, see [7,4,5]). Diedrich et al [8,9] study locomotion through the time evolution of the relative phase of the segments within a limb. In their model gaits are viewed as attractors and the walk-run transition is seen as a transition between attractors.…”

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

“…This broad spectrum of gaits raises the question of the factors that govern gait selection. Several explanations for gait transitions have been proposed based on kinematic factors (Hreljac 1995), mechanical loading, such as musculoskeletal force (Farley & Taylor 1991) and bone strain (Biewener & Taylor 1986), muscle activation (Prilutsky & Gregor 2001), mechanical restrictions (Alexander 1984) and dynamic-systems theory (Diedrich & Warren 1995;Raynor et al 2002). Margaria (1938), who investigated the walk-run transition in humans, was among the first to report a metabolic advantage of gait selection by showing that above 2 m s -1 , approximately the speed where humans change gait, walking is metabolically more expensive than running, whereas below this speed the converse is true.…”