Frans CT van der Helm

Frans CT van der Helm
Delft University of Technology | TU · Department of Biomechanical Engineering

PhD

About

310
Publications
110,271
Reads
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16,381
Citations
Citations since 2016
61 Research Items
7084 Citations
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201620172018201920202021202202004006008001,000
201620172018201920202021202202004006008001,000
Additional affiliations
December 1986 - present
Delft University of Technology
Position
  • Professor (Full)

Publications

Publications (310)
Article
Full-text available
Transcranial direct current stimulation (tDCS) is a promising tool to improve and speed up motor rehabilitation after stroke, but inconsistent clinical effects refrain tDCS from clinical implementation. Therefore, this study aimed to assess the need for individualized tDCS configurations in stroke, considering interindividual variability in brain a...
Article
Full-text available
Recent studies have established the presence of nociceptive steady-state evoked potentials (SSEPs), generated in response to thermal or intra-epidermal electric stimuli. This study explores cortical sources and generation mechanisms of nociceptive SSEPs in response to intra-epidermal electric stimuli. Our method was to stimulate healthy volunteers...
Article
Full-text available
Background: Proprioception is important for regaining motor function in the paretic upper extremity after stroke. However, clinical assessments of proprioception are subjective and require verbal responses from the patient to applied proprioceptive stimuli. Cortical responses evoked by robotic wrist perturbations and measured by electroencephalogra...
Conference Paper
Motion capture systems are extensively used to track human movement to study healthy and pathological movements, allowing for objective diagnosis and effective therapy of conditions that affect our motor system. Current motion capture systems typically require marker placements which is cumbersome and can lead to contrived movements.Here, we descri...
Article
Full-text available
A sustained sensory stimulus with a periodic variation of intensity creates an electrophysiological brain response at associated frequencies, referred to as the steady-state evoked potential (SSEP). The SSEPs elicited by the periodic stimulation of nociceptors in the skin may represent activity of a brain network that is primarily involved in nocic...
Article
Full-text available
Objective: Nonlinear modeling of cortical responses (EEG) to wrist perturbations allows for the quantification of cortical sensorimotor function in healthy and neurologically impaired individuals. A common model structure reflecting key characteristics shared across healthy individuals may provide a reference for future clinical studies investigat...
Article
Objective: This paper introduces the Cross-frequency Amplitude Transfer Function (CATF), a model-free method for quantifying nonlinear stimulus-response interaction based on phase-locked amplitude relationship. Method: The CATF estimates the amplitude transfer from input frequencies at stimulation signal to their harmonics/intermodulation at the...
Data
This dataset features the response in the human cortex to robotic manipulations of the wrist joint. The wrist joint manipulations are encoded by sensory organs in the periphery and transmitted via the spinal cord to the brain. The evoked cortical responses can be measured on the scalp using electroencephalography (EEG). Since the cortical responses...
Chapter
This paper focuses on the pathophysiology of fixed dystonia (i.e., sustained muscle contractions resulting in abnormal postures) in Complex Regional Pain Syndrome from an engineering point of view. Although the mechanisms are still elusive, the evidence implicating involvement of aberrant muscle force feedback is compelling. A neuromuscular model w...
Article
Full-text available
The human nervous system is an ensemble of connected neuronal networks. Modeling and system identification of the human nervous system helps us understand how the brain processes sensory input and controls responses at the systems level. This study aims to propose an advanced approach based on a hierarchical neural network and non-linear system ide...
Article
During movements, humans continuously regulate their joint impedance to minimize control effort and optimize performance. Joint impedance describes the relationship between a joint's position and torque acting around the joint. Joint impedance varies with joint angle and muscle activation and differs from trial-to-trial due to inherent variability...
Conference Paper
During movement, our central nervous system (CNS) takes into account the dynamics of our environment to optimally adapt our joint dynamics. In this study we explored the adaptation of shoulder joint dynamics when a participant interacted with a time-varying virtual environment created by a haptic manipulator. Participants performed a position task,...
Conference Paper
The stiffness of an Ankle-Foot-Orthosis (AFO) that aims to assist walking affects the gait biomechanics of patients with impaired gait. In patients with equinus (spastic paresis of the lower leg), impaired gait is a consequence of an increased passive ankle joint stiffness (originated from calf muscles) in combination with reduced active muscle str...
Article
Full-text available
In hemiparetic stroke, functional recovery of paretic limb may occur with the reorganization of neural networks in the brain. Neuroimaging techniques, such as magnetic resonance imaging (MRI), have a high spatial resolution which can be used to reveal anatomical changes in the brain following a stroke. However, low temporal resolution of MRI provid...
Article
Tele-manipulation of heavy loads typically requires the simultaneous use of two asymmetric slaves: a crane for vertical weight support; and a robot for accurate lateral positioning. The industrial standard prescribes a pair of operators for such tasks (one operator to control each slave), although in principle one operator might control both slaves...
Data
Brain information flow for Control 1.
Data
Brain information flow for Control 2.
Data
Brain information flow for Stroke 2.
Data
Brain information flow for Stroke 1.
Chapter
Full-text available
The human head-neck system requires continuous muscular stabilization in the presence of gravity and trunk motion. This chapter presents experimental and modelling efforts, applying mechanical perturbations to seated subjects, evaluating trunk and head motion, to investigate postural stabilization. A detailed multi-segment neck model has been deve...
Article
The quantification of mechanical power can provide valuable insight into athlete performance because it is the mechanical principle of the rate at which the athlete does work or transfers energy to complete a movement task. Estimates of power are usually limited by the capabilities of measurement systems, resulting in the use of simplified power mo...
Article
Full-text available
In searching for clinical biomarkers of the somatosensory function, we studied reproducibility of somatosensory potentials (SEP) evoked by finger stimulation in healthy subjects. SEPs induced by electrical stimulation and especially after median nerve stimulation is a method widely used in the literature. It is unclear, however, if the EEG recordin...
Article
The dynamic behavior of the wrist joint is governed by nonlinear properties, yet applied mathematical models, used to describe the measured input-output (perturbation-response) relationship, are commonly linear. Consequently, the linearly estimated model parameters will depend on properties of the applied perturbation properties (such perturbation...
Article
Background: The accuracy of source reconstruction depends on the spatial configuration of the neural sources underlying encephalographic signals, the temporal distance of the source activity, the level and structure of noise in the recordings, and - of course - on the employed inverse method. This plenitude of factors renders a definition of 'spat...
Article
Full-text available
In gait studies body pose reconstruction (BPR) techniques have been widely explored, but no previous protocols have been developed for speed skating, while the peculiarities of the skating posture and technique do not automatically allow for the transfer of the results of those explorations to kinematic skating data. The aim of this paper is to det...
Preprint
In gait studies body pose reconstruction (BPR) techniques have been widely explored, but no previous protocols have been developed for speed skating, while the peculiarities of the skating posture and technique do not automatically allow for the transfer of the results of those explorations to kinematic skating data. The aim of this paper is to det...
Chapter
Fiber tractography aims to reconstruct white matter (WM) connections in the brain. Challenges in these reconstructions include estimation of the fiber orientations in regions with multiple fiber populations, and the uncertainty in the fiber orientations as a result of noise. In this work, we use a range of multi-tensor models to cope with crossing...
Article
Certain tele-manipulation tasks require manipulation by two asymmetric slaves, for example a crane for hoisting and a dexterous robotic arm for fine manipulation. It is unclear how to best design human-in-the-loop control over two asymmetric slaves. The goal of this paper is to quantitatively compare the standard approach of two co-operating operat...
Article
Full-text available
Advice about the optimal coordination pattern for an individual speed skater, could be addressed by simulation and optimization of a biomechanical speed skating model. But before getting to this optimization approach one needs a model that can reasonably match observed behaviour. Therefore, the objective of this study is to present a verified three...
Article
Full-text available
Cortical damage after a stroke often affects movement control, resulting in impairments such as paresis and synergies. Although some recover, most stroke survivors are left with reduced function of the upper limb, which has a severe impact on their activities of daily living. People who have suffered a stroke demonstrate heterogeneous impairments d...
Article
Full-text available
Neural coupling between the central nervous system and the periphery is essential for the neural control of movement. Corticomuscular coherence is a popular linear technique to assess synchronized oscillatory activity in the sensorimotor system. This oscillatory coupling originates from ascending somatosensory feedback and descending motor commands...
Article
Objective To identify effects of a deviant motor drive in the autospectral power of dystonic muscles during voluntary contraction in cervical dystonia patients. Methods Submaximal (20%) isometric head-neck tasks were performed with the head fixed, measuring surface EMG of the sternocleidomastoid, splenius capitis and semispinalis capitis in CD pat...
Article
Full-text available
Cortical responses to continuous stimuli as recorded using either magneto- or electroencephalography (EEG) have shown power at harmonics of the stimulated frequency, indicating nonlinear behavior. Even though the selection of analysis techniques depends on the linearity of the system under study, the importance of nonlinear contributions to cortica...
Article
Full-text available
The human head-neck system requires continuous stabilization in the presence of gravity and trunk motion. We investigated contributions of the vestibulocollic reflex (VCR), the cervicocollic reflex (CCR), and neck muscle co-contraction to head-in-space and head-on-trunk stabilization, and investigated modulation of the stabilization strategy with t...
Article
Full-text available
Background Cortical damage after stroke can drastically impair sensory and motor function of the upper limb, affecting the execution of activities of daily living and quality of life. Motor impairment after stroke has been thoroughly studied, however sensory impairment and its relation to movement control has received less attention. Integrity of t...
Article
Background: Effective sensorimotor integration is essential to modulate (adapt) neck stabilization strategies in response to varying tasks and disturbances. This study evaluates the hypothesis that relative to healthy controls cervical dystonia patients have an impaired ability to modulate afferent feedback for neck stabilization with changes in t...
Article
Full-text available
To assist speed skaters in improving their skating performance, we would like to provide them with real time feedback on the orientation of the skate within a single stroke. While of course the forces generated by the skater on the ice determine the acceleration of the skater, the orientation of the skate determines in which direction this force, a...
Article
Full-text available
In baseball, pitchers are the players that are most prone to injury. Most injuries occur at the elbow and shoulder of the throwing upper limb. It is widely accepted that understanding the loading in the joints during pitching is a key factor to prevent injuries. To deepen the understanding of the joint actions this study proposes to split the net j...
Article
Full-text available
Coupling between cortical oscillations and muscle activity facilitates neuronal communication during motor control. The linear part of this coupling, known as corticomuscular coherence, has received substantial attention, even though neuronal communication underlying motor control has been demonstrated to be highly nonlinear. A full assessment of c...
Article
Full-text available
Small nerve fibers regulate local skin blood flow in response to local thermal perturbations. Small nerve fiber function is difficult to assess with classical neurophysiological tests. In this study, a vasomotor response model in combination with a heating protocol was developed to quantitatively characterize the control mechanism of small nerve fi...
Article
Biodynamic feedthrough (BDFT) refers to the feedthrough of vehicle accelerations through the human body, leading to involuntary control device inputs. BDFT impairs control performance in a large range of vehicles under various circumstances. Research shows that BDFT strongly depends on adaptations in the neuromuscular admittance dynamics of the hum...
Conference Paper
Full-text available
Push-off in speed skating requires an extensive motion strategy. During speed skating the skater continuously changes the lean and steering angle of the skate and therewith the direction of push-off. The forces in an inertial coordinate system can give insight into what amount of the push-off force is directed into the forward motion. In this paper...
Conference Paper
Full-text available
To assist speed skaters in improving their skating performance, we would like to provide them with real time feedback on the orientation of the skate within a single stroke. While of course the forces generated by the skater on the ice determine the acceleration of the skater, the orientation of the skate determines in which direction this force, a...
Article
Full-text available
Objective: This paper introduces a generalized coherence framework for detecting and characterizing nonlinear interactions in the nervous system, namely cross-spectral coherence (CSC). CSC can detect different types of nonlinear interactions including harmonic and intermodulation coupling as present in static nonlinearities and also subharmonic co...
Article
Full-text available
Communication between neuronal populations is facilitated by synchronization of their oscillatory activity. Although nonlinearity has been observed in the sensorimotor system, its nonlinear connectivity has not been widely investigated yet. This study investigates nonlinear connectivity during the human stretch reflex based on neuronal synchronizat...
Article
Full-text available
In the current project we aim to provide speed skaters with real-time feedback on how to improve their skating performance within an individual stroke. The elite skaters and their coaches wish for a system that determines the mechanical power per stroke. The push-off force of the skater is a crucial variable in this power determination. In this stu...
Article
Full-text available
Introduction: Small nerve fiber dysfunction is an early feature of diabetic neuropathy. There is a strong clinical need for a non-invasive method to assess small nerve fiber function. Small nerve fibers mediate axon reflex-related vasodilation and play an important role in thermoregulation. Assessing the reflex vasodilation after local heating mig...
Article
Dedicated pairs of isometric wrist flexion tasks, with and without visual feedback of the exerted torque, were designed to target activation of the CBL and BG in healthy subjects during functional magnetic resonance imaging (fMRI). Selective activation of the cerebellum (CBL) and basal ganglia (BG), often implicated in movement disorders such as tr...
Article
Full-text available
A musculoskeletal model of the hand and wrist can provide valuable biomechanical and neurophysiological insights, relevant for clinicians and ergonomists. Currently, no consistent data-set exists comprising the full anatomy of these upper extremity parts. The aim of this study was to collect a complete anatomical data-set of the hand and wrist, inc...
Article
Full-text available
Neural systems can present various types of nonlinear input-output relationships, such as harmonic, subharmonic, and/or intermodulation coupling. This paper aims to introduce a general framework in frequency domain for detecting and characterizing nonlinear coupling in neural systems, called the cross-frequency coherence framework (CFCF). CFCF is a...
Article
Full-text available
The goal of this study was to investigate the human ability to stabilize the trunk in space during pelvic tilt. Upper body sway was evoked in kneeling-seated healthy subjects by angular platform perturbations with a rotation around a virtual low-back pivot point between the L4 and L5 vertebrae. To investigate motor control modulation, variations in...
Article
Full-text available
Understanding movement disorder after stroke and providing targeted treatment for post stroke patients requires valid and reliable identification of biomechanical (passive) and neural (active and reflexive) contributors. Aim of this study was to assess test-retest reliability of passive, active and reflexive parameters and to determine clinical res...
Article
To facilitate the development of future shoulder endoprostheses, a long term load profile of the shoulder joint is desired. A musculoskeletal model using 3D kinematics and external forces as input can estimate the mechanical load on the glenohumeral joint, in terms of joint reaction forces. For long term ambulatory measurements, these 3D kinematics...
Conference Paper
Full-text available
A continuous somatosensory stimulation evokes a steady state response in the cortex, which can be measured using electroencephalography. We applied mechanical multisine stimulation of the wrist to investigate the properties of the steady state response in the frequency domain. Our results show a response in the contralateral sensorimotor cortex at...
Article
Full-text available
Interaction between distant neuronal populations is essential for communication within the nervous system and can occur as a highly nonlinear process. To better understand the functional role of neural interactions, it is important to quantify the nonlinear connectivity in the nervous system. We introduce a general approach to measure nonlinear con...
Conference Paper
There are several control mechanisms that contribute to keep gait stability under the presence of perturbations. For larger perturbations, responses with longer latencies produce adequate reactions to the perturbation. Latencies might be shorter, and the risk for falling might decrease provided that the reaction is adequate. It is possible that tra...
Article
When an eye is illuminated by a light coaxial with the observing eye or camera, the light is reflected by the back of the eye and a red reflex will be observed through the pupil. The intensity of this red reflex varies with the angle of eccentric gaze. The red reflex darkens as the eye fixates at the light source. Brückner described this principle...