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ABSTRACT: The long latency M2 electromyographic response of a suddenly stretched active muscle is stretch duration dependent of which the nature is unclear. We investigated the influence of the group II afferent blocker tizanidine on M2 response characteristics of the m. flexor carpi radialis (FCR). M2 response magnitude and eliciting probability in a group of subjects receiving 4 mg of tizanidine orally were found to be significantly depressed by tizanidine while tizanidine did not affect the significant linear relation of the M2 response to stretch duration. The effect of tizanidine on the M2 response of FCR is supportive of a group II afferent contribution to a compound response of which the stretch duration dependency originates from a different mechanism, e.g., rebound Ia firing.
Experimental Brain Research 11/2009; 201(4):681-8. · 2.39 Impact Factor
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ABSTRACT: Instead of hyper-reflexia as sole paradigm, post-stroke movement disorders are currently considered the result of a complex interplay between neuronal and muscular properties, modified by level of activity. We used a closed loop system identification technique to quantify individual contributors to wrist joint stiffness during an active posture task.
Continuous random torque perturbations applied to the wrist joint by a haptic manipulator had to be resisted maximally. Reflex provoking conditions were applied i.e. additional viscous loads and reduced perturbation signal bandwidth. Linear system identification and neuromuscular modeling were used to separate joint stiffness into the intrinsic resistance of the muscles including co-contraction and the reflex mediated contribution.
Compared to an age and sex matched control group, patients showed an overall 50% drop in intrinsic elasticity while their reflexive contribution did not respond to provoking conditions. Patients showed an increased mechanical stability compared to control subjects.
Post stroke, we found active posture tasking to be dominated by: 1) muscle weakness and 2) lack of reflex adaptation. This adds to existing doubts on reflex blocking therapy as the sole paradigm to improve active task performance and draws attention to muscle strength and power recovery and the role of the inability to modulate reflexes in post stroke movement disorders.
Journal of NeuroEngineering and Rehabilitation 08/2009; 6:29. · 3.26 Impact Factor
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ABSTRACT: For isometric tasks, shoulder muscle forces are assumed to scale linearly with the external arm load magnitude, i.e., muscle force ratios are constant. Inverse dynamic modeling generally predicts such linear scaling behavior, with a critical role for the arbitrary load sharing criteria, i.e., the "cost function". We tested the linearity of the relation between external load magnitude exerted on the humerus and shoulder muscle activation. Six isometric force levels ranging from 17 to 100% of maximal arm force were exerted in 24 directions in a plane perpendicular to the longitudinal axis of the humerus. The direction of maximum muscle activation, the experimentally observed so called Principal Action (PA), was determined for each force magnitude in 12 healthy subjects. This experiment was also simulated with the Delft Shoulder and Elbow Model (DSEM) using two cost functions: (1) minimizing muscle stress and (2) a compound, energy related cost function. PA, both experimental (PA(exp)) and simulated (PA(sim)), was expected not to change with arm forces magnitudes. PA(exp) of the mm. trapezius pars descendens, deltoideus pars medialis and teres major changed substantially as a function of external force magnitude, indicating external load dependency of shoulder muscle activation. In DSEM simulations, using the stress cost function, small non-linearities in the muscle force-external load dependency were observed, originating from gravitational forces working on clavicular and scapular bone masses. More pronounced non-linearities were introduced by using the compound energy related cost function, but no similarity was observed between PA(exp) and PA(sim).
Medical & Biological Engineering 05/2009; 47(5):565-72. · 1.76 Impact Factor
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ABSTRACT: Sudden stretch of active muscle typically results in two characteristic electromyographic responses: the short latency M1 and the long latency M2. The M1 response originates from the monosynaptic Ia afferent reflex pathway. The M2 response is less well understood and is likely a compound response to different afferent inputs mediated by spinal and transcortical pathways. In this study the possible contribution of the Ia afferent pathway to the M2 response was investigated. A mechanism was hypothesized in which the M1 response synchronizes the motoneurons, and therewith their refractory periods. Stretch perturbation experiments were performed on the wrist and results were compared with a computational model of a pool of motoneurons receiving tonic and Ia afferent input. The simulations showed the same stretch amplitude, velocity, and duration-dependent characteristics on the M2 as found experimentally. It was concluded that the stretch duration effect of the M2 likely originates from the proposed Ia afferent mediated mechanism.
Experimental Brain Research 01/2009; 193(4):491-500. · 2.39 Impact Factor
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Clinical Orthopaedics and Related Research 03/2004; · 2.53 Impact Factor
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ABSTRACT: OBJECTIVE: The objective of this study is to verify the assumption that the three-dimensional (3-D) shoulder motions can be described by means of an interpolation of statically recorded postures and thus, support the application of non-invasive but static techniques for motion analysis of the shoulder. BACKGROUND: During shoulder motions the scapula moves underneath the skin. Recording of motions is only possible by means of invasive methods. An alternative for the recording is palpation of skeletal landmarks on the scapula and subsequent digitization. The method is non-invasive and relatively easy, but static. Motions are modelled by means of interpolation of the subsequent position recordings. Validity of this method, however, has never been demonstrated. METHODS: Seven subjects performed an alternating abduction-adduction motion of the arm in a plane 30 degrees forward rotated with respect to the frontal plane, at three sub-maximal frequencies: 0.04, 0.25 and 0.50 Hz. The humeral and scapular motions were recorded by means of a two-dimensional (2-D) X-ray video system. The motions of the humerus, the scapular spine and the glenoid ridge were defined by angles, and the sinusoidal motion curves were characterized by means of the offset, the amplitude and the phase of the motions. RESULTS: By means of Repeated Measurements Multi-Variate Analysis of Variance, a significant effect of arm motion on the phase and the amplitude of the scapular motion was found. However, the magnitude of the effects are negligibly small for the present applications at sub-maximal arm motion velocities. CONCLUSIONS: For normal arm motions in the vertical plane, the kinematics of the shoulder skeleton can be derived by the interpolation of statically recorded positions of the bones. RELEVANCE: The 3-D motions of the shoulder are the result of the kinematic constraints of the skeletal system and the coordinated muscle forces, and are only one of the few characteristics that can be quantified. The motions contain relevant information which is essential in the analysis of clinical disorders, e.g. sub-acromial disorders and glenohumeral subluxation, the evaluation of clinical interventions and physiotherapy, and in the analysis of ergonomic and biomechanical problems.
Clinical biomechanics (Bristol, Avon) 01/1999; 13(8):593-602. · 1.76 Impact Factor
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Jurriaan H de Groot
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ABSTRACT: OBJECTIVE: The objective of this methodological study is the quantification of the sources of variability in the recorded three-dimensional motions of the shoulder mechanism for comparative purposes. BACKGROUND: The palpation and subsequent digitization of skeletal landmarks of the shoulder mechanism is a non-invasive and relatively easy method to quantify shoulder orientations. Comparison of individual motions is subject to the accuracy of the palpation method, the magnitude of kinematic redundancy of the shoulder mechanism and inter-subject differences in morphology and physiology. Quantification of these sources of variance, i.e. the palpation error, motoric noise and inter-subject differences, demonstrated the accuracy of the method and the potential validity of the descriptive motion parameters, e.g. Cardan angles, in intra- and inter-individual studies for clinical, ergonomical and biomechanical studies. METHODS: The orientations of the shoulder bones were recorded five times for each of five subjects by palpation and digitization of 12 skeletal landmarks for 10 equidistant arm elevation postures in the scapular plane. The orientations were described by means of Cardan angles. The palpation error was determined at a standardized initial rest position and expressed by Cardan angles for each recorded posture. Adding motoric noise and inter-subject differences gave the inter-individual variance. RESULTS: The palpation error was approximately 2 degrees. The major recorded variance originated from motoric noise (+/-33%) and inter-subject difference (+/-55%). CONCLUSIONS: The palpation method is an accurate means of recording the three-dimensional orientations of the shoulder mechanism and for intra-individual studies. However, inter-subject variability is large.
Clinical biomechanics (Bristol, Avon) 11/1997; 12(7-8):461-472. · 1.76 Impact Factor
