Abstract
Neuromechanical simulations have been used to study the spinal control of human locomotion which involves complex mechanical dynamics. So far, most neuromechanical simulation studies have focused on demonstrating the capability of a proposed control model in generating normal walking. As many of these models with competing control hypotheses can generate human-like normal walking behaviors, a more in-depth evaluation is required. Here, we conduct the more in-depth evaluation on a spinal-reflex-based control model using five representative gait disturbances, ranging from electrical stimulation to mechanical perturbation at individual leg joints and at the whole body. The immediate changes in muscle activations of the model are compared to those of humans across different gait phases and disturbance magnitudes. Remarkably similar response trends for the majority of investigated muscles and experimental conditions reinforce the plausibility of the reflex circuits of the model. However, the model's responses lack in amplitude for two experiments with whole body disturbances suggesting that in these cases the proposed reflex circuits need to be amplified by additional control structures such as location-specific cutaneous reflexes. A model that captures these selective amplifications would be able to explain both steady and reactive spinal control of human locomotion. Neuromechanical simulations that investigate hypothesized control models are complementary to gait experiments in better understanding the control of human locomotion.
Highlights
Understanding the control that underlies human locomotion remains a challenging problem
While some of the response trends do not match well (≤50% overlap within one s.d., comparisons marked with ∗), for the majority of the investigated muscles and experimental conditions the scaled model responses lie within one s.d. of the human responses (78% average overlap for unmarked comparisons)
By contrast, rectus femoris muscle (RF) shows response trends similar to the synergistic vasti muscle group (VAS) throughout stride, careful interpretation of these RF responses is needed, since surface EMGs of RF, which are used in the disturbance experiments, are prone to crosstalk from VAS (Nene et al, 2004)
Summary
Understanding the control that underlies human locomotion remains a challenging problem One reason for this is that many experimental techniques provide only incomplete access to the control circuits, making it impossible to directly probe the entire control involving millions of neurons in complex animals (Vogelstein et al, 2014). Another reason is that the control mechanism seems to vary across species (Orlovskiı et al, 1999; Capaday, 2002), which limits our ability to extrapolate control circuits identified with direct methods in other animals to humans (Arshavsky et al, 1985; Zehr and Stein, 1999; Moraud et al, 2016). Since bipedal locomotion emerges from the interaction between the legs and the ground by utilizing
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