Proprioceptive reflexes in patients with reflex sympathetic dystrophy

Abstract-This study aimed to analyse the dynamic properties of the muscle spindle feedback system of shoulder muscles during a posture task. External continuous force disturbances were applied at the hand while subjects had to minimize their hand displacements. The results were analysed using two frequency response functions (FRFs) from which the model parameters were derived, being 1) the mechanical admittance and 2) the reflexive impedance. These FRFs were analysed by a neuromusculoskeletal model that implicitly separates the reflexive feedback properties (position, velocity and acceleration feedback gains) from intrinsic muscle visco-elasticity. The results show substantial changes in estimated reflex gains under conditions of variable bandwidth of the applied force disturbance or variable degrees of external damping. Position and velocity feedback gains were relatively larger when the force disturbance contained only low frequencies. With increasing damping of the environment, acceleration feedback gain decreased, velocity feedback gain remained almost constant and position feedback gain increased. It is concluded that under the aforementioned circumstances, the reflex system increases its gains to maximize the mechanical resistance to external force disturbances while preserving sufficient stability.

Section: Data Processing 1) Signal Recording and Processingmentioning

confidence: 99%

Quantifying Proprioceptive Reflexes During Position Control of the Human Arm

Schouten

Vlugt

Hilten

et al. 2008

“…Continuous random force disturbances proved to be useful to quantify the functional contribution of reflexes around the shoulder during active tasks [7]- [9]. Force disturbances with position tasks (minimize displacements) are unambiguous and natural for the subject: the subject must actively control the position and preserve stability.…”

mentioning

confidence: 99%

“…High effort tasks like "minimize displacements" [7]- [9] demand high levels of cocontraction. This implies that the variation in the muscle activation due to reflexes will be relatively small as compared to the high tonic muscle activity.…”

mentioning

confidence: 99%

Design of Perturbation Signals for the Estimation of Proprioceptive Reflexes

Schouten

Vlugt

Helm

2008

Abstract-This study aimed to identify the functional contribution of reflexes to human motor control during posture maintenance. Continuous random force disturbances were applied at the hand while the subjects were instructed to minimize the deviation resulting from the force disturbances. The results were analyzed in the frequency domain with frequency response functions (FRFs). Two FRFs were evaluated: 1) the mechanical admittance and 2) the reflexive impedance, expressing the dynamic relation between position and muscle activation (assessed via electromyography, EMG). The reflexive impedance is a direct measure of the proprioceptive reflexes. To record all relevant dynamical characteristics of the arm, wide bandwidth signals were used as force disturbance. Distributing the power of the signal over fewer frequencies within the bandwidth improved the signal-to-noise-ratio SNR of the EMG recordings, facilitating reliable estimation of the reflexive impedance. The coherence indicated that the relation between force disturbance and EMG is linear under the given conditions and improved with the SNR. The method of designing disturbance signals and the estimation of the reflexive impedance are useful for studies aiming to quantify proprioceptive reflexes and to investigate its functionality.

“…Under healthy condition, humans can adapt their reflexive motor control flexibly and optimally to such varying loads, but patients with central neural disorders like stroke are not able to do so [49].…”

Section: Discussionmentioning

confidence: 99%

Sensing Power Transfer Between the Human Body and the Environment

Veltink

Kortier

Schepers

2009

Abstract-The power transferred between the human body and the environment at any time and the work performed are important quantities to be estimated when evaluating and optimizing the physical interaction between the human body and the environment in sports, physical labor, and rehabilitation. It is the objective of the current paper to present a concept for estimating power transfer between the human body and the environment during free motions and using sensors at the interface, not requiring measurement systems in the environment, and to experimentally demonstrate this principle. Mass and spring loads were moved by hand over a fixed height difference via varying free movement trajectories. Kinematic and kinetic quantities were measured in the handle between the hand and the load. 3-D force and moments were measured using a 6 DOF force/moment sensor module, 3-D movement was measured using 3-D accelerometers and angular velocity sensors. The orientation was estimated from the angular velocity, using the initial orientation as a begin condition. The accelerometer signals were expressed in global coordinates using this orientation information. Velocity was estimated by integrating acceleration in global coordinates, obtained by adding gravitational acceleration to the accelerometer signals. Zero start and end velocities were used as begin and end conditions. Power was calculated as the sum of the inner products of velocity and force and of angular velocity and moment, and work was estimated by integrating power over time. The estimated performed work was compared to the potential energy difference corresponding to the change in height of the loads and appeared to be accurate within 4% for varying movements with net displacements and varying loads (mass and spring). The principle of estimating power transfer demonstrated in this paper can be used in future interfaces between the human body and the environment instrumented with body-mounted miniature 3-D force and acceleration sensors.