Bipedal locomotion is a phenomenon that still eludes a fundamental and
concise mathematical understanding. Conceptual models that capture some
relevant aspects of the process exist but their full explanatory power is not
yet exhausted. In the current study, we introduce the robustness criterion
which defines the conditions for stable locomotion when steps are taken with
imprecise angle of attack. Intuitively, the necessity of a higher precision
indicates the difficulty to continue moving with a given gait. We show that the
spring-loaded inverted pendulum model, under the robustness criterion, is
consistent with previously reported findings on attentional demand during human
locomotion. This criterion allows transitions between running and walking, many
of which conserve forward speed. Simulations of transitions predict Froude
numbers below the ones observed in humans, nevertheless the model
satisfactorily reproduces several biomechanical indicators such as hip
excursion, gait duty factor and vertical ground reaction force profiles.
Furthermore, we identify reversible robust walk-run transitions, which allow
the system to execute a robust version of the hopping gait. These findings
foster the spring-loaded inverted pendulum model as the unifying framework for
the understanding of bipedal locomotion.Comment: unpublished, in preparatio