Biology subjects

Aoi, S.

Publications and source records attributed to Aoi, S..

5 recordsLinked to original sources

bioRxiv2025

Gait transition mechanism from quadrupedal to bipedal locomotion in the Japanese macaque based on inverted pendulum

The ability of non-human primates to transition from quadrupedal to bipedal locomotion offers critical insights into both the evolution of human bipedalism and the principles of complex motor control. While quadrupedal and bipedal gaits in non-human primates have been studied, the dynamic mechanisms underlying the transition between these gaits remain poorly understood. Japanese macaques trained to walk bipedally have been reported to utilize inverted pendulum dynamics to achieve efficient bipedal locomotion. Given the intrinsic instability of inverted pendulum systems, which can induce large changes in movement with minimal control input, we hypothesized that this mechanism also contributes to the gait transition. To test this, we developed a neuromusculoskeletal model of the Japanese macaque that integrates a detailed musculoskeletal structure with a physiologically inspired motor control system. Through forward dynamics simulations, we generated a variety of movement patterns by systematically parameterizing motor commands, including failed transitions that are difficult to capture experimentally. We then applied dynamical systems analysis using on an inverted pendulum model to examine the underlying principles of the transition process. Our results demonstrate that successful gait transitions depend on generating an inverted pendulum motion through appropriate control of the forward step length of one hindlimb. These findings provide mechanistic insights into how Japanese macaques coordinate their complex musculoskeletal systems to perform skilled, full-body movements in the gait transition, offering a deeper understanding of both advanced motor control and the evolution of human bipedalism.

neuroscience↗

bioRxiv2025

Mechanisms of adaptive interlimb coordination to sudden ground loss: a neuromusculoskeletal modeling study

Mammals exhibit robust walking across diverse environments, a capability largely attributed to central pattern generators (CPGs) in the spinal cord. Afferent feedback modulates CPG output and plays a critical role in adaptive locomotion, yet its specific contributions remain poorly understood. To investigate this, we used a neuromusculoskeletal model to simulate hindlimb locomotion in spinalized cats encountering a hole and experiencing a sudden loss of ground support, as described in prior experimental studies. The model couples a trunk-andhindlimb musculoskeletal system to a pair of two-level, half-center CPGs--one for each hindlimb. The model reproduced the observed adaptive interlimb coordination that allows cats to maintain walking after the sudden loss of ground support. Notably, the adaptive response emerged without re-optimizing parameters, which were tuned for steady walking in an environment without holes. Nullcline analysis based on dynamical systems theory revealed that afferent feedback mechanisms controlling the transitions between fast and slow neuronal dynamics facilitated adaptive interlimb coordination. These findings provide mechanistic insight into how spinal feedback circuits support robust locomotion through dynamic interactions between the nervous system, the musculoskeletal system, and the environment.

neuroscience↗

bioRxiv2024

Bayesian estimation of trunk-leg coordination during walking using phase oscillator models

In human walking, the legs and other body parts coordinate to produce a rhythm with appropriate phase relationships. From the point of view for rehabilitating gait disorders, such as Parkinson Disorders, it is important to understand the control mechanism of the gait rhythm. A previous study showed that the antiphase relationship of the two legs during walking is not strictly controlled using the reduction of the motion of the legs during walking to coupled phase oscillators. However, the control mechanisms other than those of the legs remains unknown. In particular, the trunk moves in tandem with the legs and must play an important role in stabilizing walking because it is above the legs and accounts for more than half of the mass of the human body. This study aims to uncover the control mechanism of the leg-trunk coordination in the sagittal plane using the coupled phase oscillators model and Bayesian estimation. We demonstrate that the leg-trunk coordination is not strictly controlled, as well as the interleg coordination.

bioengineering↗

bioRxiv2023

Interleg coordination is not strictly controlled during walking

In human walking, the left and right legs move alternately, half a stride out of phase with each other. Although various parameters, such as stride frequency, stride length, and duty factor, vary with walking speed, the antiphase relationship of the leg motion remains unchanged. This is the case even during running. However, during walking in left-right asymmetric situations, such as walking with unilateral leg loading, walking along a curved path, and walking on a split-belt treadmill, the relative phase between left and right leg motion shifts from the antiphase condition to compensate for the asymmetry. In addition, the phase relationship fluctuates significantly during walking of elderly people and patients with neurological disabilities, such as those caused by stroke or Parkinsons disease. These observations suggest that appropriate interleg coordination is important for adaptive walking and that interleg coordination is strictly controlled during walking of healthy young people. However, the control mechanism of interleg coordination remains unclear. In the present study, we derive a quantity that models the control of interleg coordination during walking of healthy young people by taking advantage of a state-of-the-art method that combines big data science with nonlinear dynamics. This is done by modeling this control as the interaction between two coupled oscillators through the phase reduction theory and Bayesian inference method. However, the results were not what we expected. Specifically, we found that the relative phase between the motion of the legs is not actively controlled until the deviation from the antiphase condition exceeds a certain threshold. In other words, the control of interleg coordination has a dead zone like that in the case of the steering wheel of an automobile. Such forgoing of control presumably enhances energy efficiency and maneuverability during walking. Furthermore, the forgoing of control in specific situations, where we expect strict control, also appears in quiet standing. This suggests that interleg coordination in walking and quiet standing have a common characteristic strategy. Our discovery of the dead zone in the control of interleg coordination not only provides useful insight for understanding gait control in humans, but also should lead to the elucidation of the mechanisms involved in gait adaptation and disorders through further investigation of the dead zone.

bioengineering↗

bioRxiv2020

Dynamical determinants of different spine movements and gait speeds in rotary and transverse gallops

Quadruped gallop is categorized into two types: rotary and transverse. While the rotary gallop involves two types of flight with different spine movements, the transverse gallop involves only one type of flight. The rotary gallop can achieve faster locomotion than the transverse gallop. To clarify these mechanisms from a dynamic viewpoint, we developed a simple model and derived periodic solutions by focusing on cheetahs and horses. The solutions gave a criterion to determine the flight type: while the ground reaction force does not change the direction of the spine movement for the rotary gallop, it changes for the transverse gallop, which was verified with the help of animal data. Furthermore, the criterion provided the mechanism by which the rotary gallop achieves higher-speed than the transverse gallop based on the flight duration. These findings improve our understanding of the mechanisms underlying different gaits that animals use.

bioinformatics↗