Biology subjects

Geijtenbeek, T.

Publications and source records attributed to Geijtenbeek, T..

6 recordsLinked to original sources

bioRxiv2025

A simple network of proprioceptive reflexes can produce a variety of bipedal gaits

Proprioception is crucial for movement, yet the role of proprioceptive reflexes in legged locomotion is still poorly understood. While previous simulation studies have shown great potential for reflex-based control strategies, these controllers are typically catered to specific gaits, using hand-crafted feedback pathways that are linked to specific gait phases. In this work, we explore the control capabilities of a simple reflex controller that consists of only monosynaptic and antagonistic length and force feedback pathways with constant gains. Despite its simplicity, we found our control framework capable of producing a wide variety of natural gaits, including walking and hopping, forwards and backwards, and running in different variations and at different velocities - without requiring any rhythmic inputs or high-level state machines modulating the feedback gains. Our work highlights the important role and flexibility of proprioceptive reflexes and suggests a necessary re-evaluation of their role in locomotion. Due to its simplicity and flexibility, our control framework provides a solid basis for the development of higher level neuromuscular control systems. Author summaryHuman locomotion is characterized by an impressive versatility and humans transition naturally between different gaits. However, the neural mechanisms underlying human motor control are not fully understood and remain controversial. The two widely accepted basic components of the neural circuitry involved in locomotion are central pattern generators (CPG) and spinal reflexes, leading to a long-standing debate on their respective roles. Neuromusculoskeletal models can be employed to study the role of these neural control structures in simulation. Until now, these models mostly focus on walking and require an additional component like a state-machine or CPG besides reflexes to generate rhythmic activation of muscles. In this work, we propose a controller that can generate different rhythmic gaits like walking and hopping, forwards and backwards, as well as running, based solely on simple reflexes known to exist in the mammalian spinal cord. We challenge the current view of the role of rhythm-generating components and show the remarkable potential of reflexes for locomotion control. To our knowledge, this is the first work showing that versatile locomotion can be achieved solely based on reflexes without the need of a CPG. Our results contribute to the understanding of human motor control and are relevant for the control of robots, exoskeletons, prostheses and ortheses.

biophysics↗

bioRxiv2023

A planar neuromuscular controller to simulate age-related adaptation strategies in the sit-to-walk movement.

Standing up from a chair is a key daily life activity that is sensitive to functional limitations as we age and associated with falls, frailty, and institutional living. Predictive neuromusculoskeletal models can potentially shed light on the interconnectivity and interdependency of age-related changes in neuromuscular capacity, reinforcement schemes, sensory integration, and adaptation strategies during stand-up. Most stand-up movements transfer directly into walking (sit-to-walk). The aim of this study was to develop and validate a neuromusculoskeletal model with reflex-based muscle control that enables simulation of the sit-to-walk movement under various conditions (seat height, foot placement). We developed a planar sit-to-walk musculoskeletal model (11 degrees-of-freedom, 20 muscles) and neuromuscular controller, consisting of a two-phase stand-up controller and a reflex-based gait controller. The stand-up controller contains generic neural pathways of delayed proprioceptive feedback from muscle length, force, velocity, and upper-body orientation (vestibular feedback) and includes both monosynaptic an antagonistic feedback pathways. The control parameters where optimized using a shooting-based optimization method, based on a high-level optimization criterium. Simulations were compared to recorded kinematics, ground reaction forces, and muscle activation. The simulated kinematics resemble the measured kinematics and muscle activations. The adaptation strategies that resulted from alterations in seat height, are comparable to those observed in adults. The simulation framework and model are publicly available and allow to study age-related compensation strategies, including reduced muscular capacity, reduced neural capacity, external perturbations, and altered movement objectives.

bioengineering↗

bioRxiv2023

Antibodies against SARS-CoV-2 control complement-induced inflammatory responses to SARS-CoV-2

Dysregulated immune responses contribute to pathogenesis of COVID-19 leading to uncontrolled and exaggerated inflammation observed during severe COVID-19. However, it remains unclear how immunity to SARS-CoV-2 is induced and subsequently controlled. Notably, here we have uncovered an important role for complement in the induction of innate and adaptive immunity to SARS-CoV-2. Complement rapidly opsonized SARS-CoV-2 via the lectin pathway. Complement-opsonized SARS-CoV-2 efficiently interacted with dendritic cells (DCs), inducing type I IFN and pro-inflammatory cytokine responses, which were inhibited by antibodies against the complement receptors (CR)3 and CR4. These data suggest that complement is important in inducing immunity via DCs in the acute phase against SARS-CoV-2. Strikingly, serum from COVID-19 patients as well as monoclonal antibodies against SARS-CoV-2 attenuated innate and adaptive immunity induced by complement-opsonized SARS-CoV-2. Blocking the FcyRII, CD32, restored complement-induced immunity. These data strongly suggest that complement opsonization of SARS-CoV-2 is important for inducing innate and adaptive immunity to SARS-CoV-2. Subsequent induction of antibody responses is important to limit the immune responses and restore immune homeostasis. These data suggest that dysregulation in complement and FcyRII signalling might underlie mechanisms causing severe COVID-19.

immunology↗

bioRxiv2022

Minimization of metabolic cost of transport predicts changes in gait mechanics over a range of ankle-foot orthosis stiffnesses in individuals with bilateral plantar flexor weakness

Neuromuscular disorders often lead to ankle plantar flexor muscle weakness, which impairs ankle push-off power and forward propulsion during gait. To improve walking speed and reduce metabolic cost of transport (mCoT), patients with plantar flexor weakness are provided dorsal-leaf spring ankle-foot orthoses (AFOs). The mCoT during gait depends on the AFO stiffness where an optimal AFO stiffness exists that minimizes mCoT. The biomechanics of why and how there exists a unique optimal stiffness for individuals with plantar flexor weakness are not well understood. To help understand why, we hypothesized that gait adaptations can be predicted by mCoT minimization. To explain how, we hypothesized that the AFO would reduce the required support moment and, hence, metabolic costs from the ankle plantar flexor and knee extensor muscles during stance and reduce hip flexor metabolic cost to initiate swing. To test these hypotheses, we generated neuromusculoskeletal simulations to represent gait of an individual with bilateral plantar flexor weakness wearing an AFO with varying stiffness. Predictions were predicated on the goal of minimizing mCoT at each stiffness level, and the motor patterns were determined via dynamic optimization. The simulation results were compared to experimental data from subjects with bilateral plantar flexor weakness walking with varying AFO-stiffness. Our simulations demonstrated that minimization of mCoT predicts gait adaptations in response to varying AFO stiffness levels in individuals with bilateral plantar flexor weakness. Initial reductions in mCoT with increasing stiffness were attributed to reductions in quadriceps metabolic cost during midstance. Increases in mCoT above optimum stiffness were attributed to the increasing metabolic cost of both hip flexor and hamstrings muscles. The insights gained from our simulations could inform clinicians on the prescription of personalized AFOs. With further model individualization, simulations based on mCoT minimization may sufficiently predict adaptations to an AFO in individuals with plantar flexor weakness. Author SummaryNeuromuscular disorders like stroke, Charcot-Marie-Tooth disease, and poliomyelitis often lead to calf muscle weakness, which makes walking slower and more demanding. To improve walking speed and reduce energy demand, patients with calf muscle weakness are frequently provided ankle-foot orthoses (AFOs). The energy demand of walking is affected by the AFOs stiffness and there is a stiffness that minimizes the energy demand for an individual with calf weakness. To uncover the optimal stiffness, we generated simulations of an individual with calf muscle weakness walking with an AFO over a range of stiffnesses. Stable walking patterns were generated that minimized the energy demand for a given stiffness. We found that the initial reductions in energy demand as stiffness increased, were attributed to reductions in quadriceps muscle energy. Increases in energy demand as stiffness increased above the optimum were attributed to the increased energetic cost of both hip flexor and hamstrings muscles. With further model individualization, we believe that simulations based on minimizing the energy demand of movement can sufficiently predict adaptations to an AFO. Simulations can enable the prescription of personalized AFOs for individuals with neuromuscular disorders that help them walk with sufficient speed and efficiency to keep up with their peers.

bioengineering↗

bioRxiv2022

Self-paced treadmill controller algorithm based on position and speed of centre of mass

BackgroundSelf-paced treadmills are increasingly used in clinical and research settings. Using self-paced (SP) treadmills, researchers can simulate overground walking while participants can walk with different but comfortable gait speeds in a controlled environment. Several algorithms have been designed for self-paced treadmills based on data from force plates, motion capture, and even marker-less systems such as 3D depth cameras. MethodsWe present a non-linear controller that implements a self-paced algorithm integrated with treadmills. This algorithm uses the subjects centre-of-mass (CoM) position and velocity, relative to the front and back end of the treadmill as inputs. The controller continuously adjusts the treadmills belt speed via belt acceleration. The algorithm attempts to prevent the subject reaching the front and back of treadmill via minimal treadmill acceleration. FindingsThis method has been safely used in previous studies with over 410 subjects in various populations. We simulated the use of the SP algorithm with three different sensitivities (0.2, 1 and 2). The belt speed predicted by algorithm simulation in matched well with the belt speeds of experiments in (Gait Realtime Analysis Interactive Lab (GRAIL) system. InterpretationThis algorithm is integrated with a VR environment in which the subject can be immersed and even be mechanically perturbed. Additionally, this algorithm can be implemented in other treadmills where CoM position is known. We encourage researchers to use and build upon our well-established SP algorithm toward a more standardized SP algorithm in different gait scenarios across various instrumented treadmills with different populations.

bioengineering↗

bioRxiv2019

Predicting gait adaptations due to ankle plantarflexor muscle weakness and contracture using physics-based musculoskeletal simulations

Deficits in the ankle plantarflexor muscles, such as weakness and contracture, occur commonly in conditions such as cerebral palsy, stroke, muscular dystrophy, and Charcot-Marie-Tooth disease. While these deficits likely contribute to observed gait pathologies, elucidating cause-effect relationships is difficult due to the often co-occurring biomechanical and neural deficits. To elucidate the effects of weakness and contracture, we systematically introduced isolated deficits into a musculoskeletal model and generated simulations of walking to predict gait adaptations due to these deficits. We developed a planar model containing 9 degrees of freedom and 18 musculotendon actuators, and an optimization framework through which we imposed simple objectives, such as minimizing cost of transport while avoiding falling and injury, and maintaining head stability. We first validated that our model could generate gaits that reproduced experimentally observed kinematic, kinetic, and metabolic trends for two cases: 1) walking at prescribed speeds between 0.50 m/s and 2.00 m/s and 2) walking at self-selected speed. We then applied mild, moderate, and severe levels of muscle weakness or contracture to either the soleus (SOL) or gastrocnemius (GAS) or both of these major plantarflexors (PF) and retrained the model to walk at a self-selected speed. The model was robust to all deficits, finding a stable gait in all cases. Severe PF weakness caused the model to adopt a slower, \"heel-walking\" gait. Severe contracture of only SOL or both PF yielded similar results: the model adopted a \"toe-walking\" gait with excessive hip and knee flexion during stance. These results highlight how plantarflexor weakness and contracture may contribute to observed gait patterns. Our model, simulation and optimization framework, and results are freely shared so that others can reproduce and build upon our work.\n\nAuthor summaryDeficits in the muscles that extend the ankle are thought to contribute to abnormal walking patterns in conditions such as cerebral palsy, stroke, muscular dystrophy, and Charcot-Marie-Tooth disease. To study how deficits in these muscles contribute to abnormal walking patterns, we used computer simulations to systematically introduce muscle deficits into a biomechanically accurate model. We first showed that our model could discover realistic walking patterns over a wide range of speeds when we posed a simple objective: walking while consuming a minimum amount of energy per distance, maintaining head stability, and avoiding injury. We then used the model to study the effect of two commonly observed problems: muscle weakness and muscle tightness. We found that severe weakness of the ankle extensors caused the model to adopt a slower, \"heel-walking\" gait, and severe tightness caused the model to adopt a crouched, \"toe-walking\" gait. These results highlight how deficits in the ankle extensor muscles may contribute to abnormal walking patterns commonly seen in pathological populations.

bioengineering↗