The Landscape of Movement Control in Locomotion: Cost, Strategy, and Solution

Abstract

Features of gait are determined at multiple levels, from the selection of the gait itself (e.g., walk or run) through the specific parameters utilized (stride length, frequency, etc.) to the pattern of muscular excitation. The ultimate choices are determined neurally, but what is involved with deciding on the appropriate strategy? Human locomotion appears stereotyped not so much because the pattern is predetermined, but because these movement patterns are good solutions for providing movement utilizing the machinery available to the individual (the legs and their requisite components). Under different circumstances the appropriate solution may differ broadly (different gait) or subtly (different parameters). Interpretation of the neural decision making process would benefit from understanding the influences that are utilized in the selection of the appropriate solution in any set of circumstances, including normal conditions. In this review we survey an array of studies that point to energetic cost as a key input to the gait coordination system, and not just an outcome of the gait pattern implemented. We then use that information to rigorously define the construct proposed by Sparrow and Newell (1998) where the effects of environment, organism, and task act as constraints determining the solution set available, and the coordination pattern is then implemented under pressure for energetic economy. The fit between the environment and the organism define affordances that can be actualized. We rely on a novel conceptualization of task that recognizes that the task goal needs to be separated from the mechanisms that achieve it so that the selection of a particular implementation strategy can be exposed and understood. This reformulation of the Sparrow and Newell construct is then linked to the proposed pressure for economy by considering it as an optimization problem, where the most readily selected gait strategy will be the one that achieves the task goal at (or near) the energetic minimum.

Rapid and robust patterns of spontaneous locomotor deficits in mouse models of Huntington’s disease

“…Mammalian locomotion is composed of a sequence of musculoskeletal positions to exert force [1,2] and, when compromised, organisms can adapt and uncouple these components to prioritize efficiency [3][4][5]. These adaptations for the economy of movement can be measured as changes in gait.…”

Step time asymmetry but not step length asymmetry is adapted to optimize energy cost of split‐belt treadmill walking

“…Energetic cost landscapes outline how modifying a given gait parameter affects energy cost and thereby identify the value of a given gait parameter associated with the lowest cost in walking (Croft et al . 2019). During tied‐belt treadmill walking with the belts running at the same speed, symmetry in step times is energetically optimal (Ellis et al .…”

“…Complementary to the idea of error-based learning, split-belt treadmill adaptation may also reflect energy optimization (Finley et al 2013). Energetic cost landscapes outline how modifying a given gait parameter affects energy cost and thereby identify the value of a given gait parameter associated with the lowest cost in walking (Croft et al 2019). During tied-belt treadmill walking with the belts running at the same speed, symmetry in step times is energetically optimal (Ellis et al 2013), but it is unknown how step time asymmetry affects the energetic cost landscape during split-belt treadmill walking.…”

Form in the context of function: Fundamentals of an energy effective striding walk, the role of the plantigrade foot and its expected size

“…For biological systems, limiting energetic expense is of paramount concern (Alexander, 2001; Ruina et al, 2005). Although the concept of these losses have been suggested for some time (e.g., Alexander, 1991; Bekker, 1956; McGeer, 1990; Rashevsky, 1948) it is not until recently that their effect on walking dynamics has been fully appreciated (Bertram & Hasaneini, 2013; Croft, Schroeder, & Bertram, 2019b; Hasaneini, Macnab, Bertram, & Leung, 2013; Kuo, Donelan, & Ruina, 2005; Ruina et al, 2005). Consequently, it is necessary to understand this aspect of locomotion in order to interpret the role of movements and morphology that produces energetically effective walking, as displayed by modern humans and any stages on the path to the modern result.…”