vendex and Muscle-Rigidity

1. Quantification of the effect on rigidity of its 'activation', by isometric grip, of standardized pressure, of the contralateral hand, was explored. Torque required to move the forearm through a fixed angle of 40 degrees, at a controlled rate of 0.5 Hz, in a horizontal plane about a pivotal axis aligned to the elbow joint, was recorded before (12 'baseline' recordings), during (10), and after (> or = 8) activation. Work required per unit displacement was calculated. 2. Specificity: Pilot serial daytime measurements gave an overall mean ratio, work required on activation over baseline, of 2.94 (95% CI 2.53, 3.42) in two elderly untreated parkinsonians, and 3.19 (2.75, 3.71) in two elderly subjects with isolated, clinically activation phenomenon, compared with 1.90 (1.64, 2.21) in two elderly without (P < 0.001), whilst two young adults did not activate, 0.98 (0.85, 1.14). In elderly subjects, work required under activation decreased during the day in health (-10 (-5, -14)% h-1, P = 0.0002), showed no significant change in those with clinical activation (4 (-1, 9)% h-1), and increased in parkinsonians (6 (0, 12)% h-1, P = 0.05): there appeared to be a transitionary state. 3. Validation of methodology: Quantifying the same work ratio on a single occasion in 20 aged parkinsonians (P), their spouses (Ps), 20 index controls (C) without parkinsonism, matched to (P), and their spouses (Cs) gave corroborative evidence of a pre-clinical state, defined by other measurements, in the spouses of sufferers. Values for C, Cs and Ps, 1.89 (1.42, 2.52), 2.38 (1.79, 3.17) and 2.93 (2.20, 3.90) respectively, were in consecutive positions, from health to (P, 2.96 (2.22, 3.95)) disease (P = 0.001 for Ps c.f. C; P = 0.1 for Ps c.f. Cs). Data on change over the day may enhance discrimination. 4. Sensitivity to medicines was illustrated, in two parkinsonians, by randomised, placebo balanced and controlled challenges: 1 and 2 tablets, Sinemet CR (Du Pont Pharmaceuticals, each levodopa 200 mg/carbidopa 50 mg) and 1 tablet, Sinemet-Plus (levodopa 100 mg/carbidopa 25 mg), then two 2 mg tablets, benzhexol. The dopaminergic effect (P < 0.001) was selective for activation (treatment.test-condition interaction, P = 0.004), and showed the expected time profiles. The effect of benzhexol (P = 0.008) lacked such selectivity. Its onset (> 4, < or = 6 h) was delayed, compatible with a gastrointestinal anti-muscarinic action and the subjects' ages. 5. Reliability (Fleiss's criterion) was show

Topics: Adult; Aged; Antiparkinson Agents; Carbidopa; Delayed-Action Preparations; Drug Combinations; Female; Hand Strength; Humans; Isometric Contraction; Levodopa; Male; Muscle Rigidity; Parkinson Disease; Physical Exertion; Reproducibility of Results; Sensitivity and Specificity; Torque; Trihexyphenidyl

Quantitative assessment of the muscle tone is important when studying patients with neurological disorders such as Parkinson's disease (PD). For the assessment of therapeutic progress, quantitative and objective outcome measures are needed. This article presents a novel electromechanical device to monitor the quantitative rigidity of the wrist joint against passive movement. The novel device is equipped with an electrical motor to move the wrist joint in a flexion-extension manner with different velocity profiles. The accuracy of the device was measured in terms of position, velocity and torque accuracy. The feasibility of the measurement procedure was tested in a pilot study with four PD patients and 12 healthy controls (HC), at velocities of 10 °/s,50 °/s, and 100 °/s. {The position and velocity of the developed device were (0.005 ± 0.105)° and (0.734 ±0.276) °/s, unloaded, and (0.003 ± 0.113) ° and (0.013 ± 0.038) °/s, loaded with a relaxed arm, respectively. The torque accuracy was (15.029 ± 2.235) mNm. The comparison of the median rigidity between the PD patients and HC showed significant differences at all tested velocities, during both flexion and extension movements. This device proved to have sufficient accuracy and sensitivity to precisely measure the interaction torque at the wrist joint and to differentiate PD rigidity from normal muscle tone. The device, thus provides a quantitative and objective measure of rigidity in PD.

Topics: Humans; Muscle Rigidity; Parkinson Disease; Pilot Projects; Torque; Wrist; Wrist Joint

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by rigidity, bradykinesia, resting tremor, and postural instability. Rigidity, defined as an increased resistance to passive movement of a joint, progresses faster than other motor signs in PD. Rigidity is attributable to both exaggerated neural reflex and altered muscle mechanical properties. However, little is known about the contributions of individual components to rigidity. Further, there is no evidence regarding the effects of dopaminergic medication on individual components. Objectives of this study were to quantify the contributions of neural reflexes and intrinsic muscle properties to rigidity and investigate the effects of medication on each contributing component. Joint torque and muscle activities of the wrist in 14 patients and 14 controls were measured during externally induced movements. Each subject with PD was tested in Off- and On-medication states. A system identification technique was applied to differentiate and quantify the neural reflex and intrinsic mechanical components. A mixed model of ANOVA was performed to compare the differences between the two components of rigidity for both groups, and to compare between the Off- and On-medication states for patients. The results showed that reflex and intrinsic components are comparable (p > 0.05), and both are enhanced in subjects with PD than in the controls (p < 0.05). Medication decreased the reflex component of rigidity (p < 0.01). It is concluded that both reflex and intrinsic factors are responsible for rigidity. Present findings are clinically significant as they may provide guidance in development of effective therapeutic interventions.

Topics: Aged; Analysis of Variance; Case-Control Studies; Electromyography; Female; Humans; Male; Middle Aged; Movement; Muscle Contraction; Muscle Rigidity; Parkinsonian Disorders; Reflex, Stretch; Torque

Quantify the effects of increased amplitude and rate of muscle stretch on parkinsonian rigidity.. Eighteen subjects with Parkinson's disease participated in this study. Subjects' tested hand was passively displaced through 60° and 90° ranges of wrist flexion and extension at velocities of 50°/s and 280°/s in both treated and untreated conditions. Joint angular position, resistance torque, and surface electromyography (EMG) of the wrist flexors and extensors were recorded. Rigidity was quantified by normalized work scores and normalized angular impulses for flexion and extension, separately. Reflex responses of stretched and shortened muscles were quantified by mean EMG and EMG ratio. A series of ANOVAs was performed to determine the effect of amplitude, velocity and medication on selected variables.. Both work scores and angular impulses revealed that the larger displacement amplitude and the higher velocity were associated with significantly greater rigidity, increased EMG ratio and mean EMG of stretched muscles. Dopaminergic medication was not associated with a reduction in rigidity.. Parkinsonian rigidity is modulated by the amplitude and rate of muscle stretch.. These findings shed light on the biomechanical underpinnings and physiological characteristics of rigidity and may inform clinical rigidity assessment in Parkinson's disease.

Topics: Aged; Analysis of Variance; Antiparkinson Agents; Data Interpretation, Statistical; Electromyography; Female; Humans; Male; Middle Aged; Movement; Muscle Rigidity; Muscle, Skeletal; Parkinson Disease; Reflex, Stretch; Torque; Wrist

Low-frequency oscillations in the basal ganglia are prominent in patients with Parkinson's disease off medication. Correlative and more recent interventional studies potentially implicate these rhythms in the pathophysiology of Parkinson's disease. However, effect sizes have generally been small and limited to bradykinesia. In this study, we investigate whether these effects extend to rigidity and are maintained in the on-medication state. We studied 24 sides in 12 patients on levodopa during bilateral stimulation of the STN at 5, 10, 20, 50, 130 Hz and in the off-stimulation state. Passive rigidity at the wrist was assessed clinically and with a torque-based mechanical device. Low-frequency stimulation at ≤20 Hz increased rigidity by 24 % overall (p = 0.035), whereas high-frequency stimulation (130 Hz) reduced rigidity by 18 % (p = 0.033). The effects of low-frequency stimulation (5, 10 and 20 Hz) were well correlated with each other for both flexion and extension (r = 0.725 ± SEM 0.016 and 0.568 ± 0.009, respectively). Clinical assessments were unable to show an effect of low-frequency stimulation but did show a significant effect at 130 Hz (p = 0.002). This study provides evidence consistent with a mechanistic link between oscillatory activity at low frequency and Parkinsonian rigidity and, in addition, validates a new method for rigidity quantification at the wrist.

Topics: Deep Brain Stimulation; Female; Humans; Male; Middle Aged; Muscle Rigidity; Parkinson Disease; Torque; Wrist

This study aims to analyze viscoelastic properties of the wrist in patients with Parkinson's disease (PD) in comparison with the clinical score of severity. Forty-five patients with PD and 12 healthy volunteers participated in this study. Severity of rigidity at the wrist was rated by a neurologist just before the experiment. Wrist joint torque resistive to the imposed movement was measured. Three different models, (identical in structure, only different in the number of parameters for extension and flexion phases) were used in identification of viscoelastic properties: 1) one damping constant and one spring constant throughout all phases, 2) two damping constants for each phase and one spring constant throughout all phases, and 3) two damping constants and two spring constants for each phase. Normalized work and impulse suggested in the literature were also calculated. Spring constants of different models and phases showed comparable correlation with rigidity score ( r=0.68-0.73). In terms of the correlation of damping constant with clinical rigidity score, model 1 ( r = 0.90) was better than models 2 and 3 ( r=0.59 - 0.71). These results suggest that the clinical rigidity score is better represented by the mean viscosity during both flexion and extension. In models with two dampers (model 2 and 3), the damping constant was greater during extension than flexion in patients , in contrast that there was no phase difference in normal subjects. This suggests that in contrast with normal subjects, phase-dependent viscosity may be an inherent feature of PD. Although work and impulse were correlated with clinical rigidity score ( r = 0.11 - 0.84), they could not represent the phase-dependent rigidity inherent in PD. In conclusion, the viscosity of model 1 would be appropriate for quantification of clinical ratings of rigidity and that of model 2 for distinction of PD and also for investigation of phase-dependent characteristics in parkinsonian rigidity.

Topics: Aged; Aged, 80 and over; Biomechanical Phenomena; Elasticity; Female; Hand; Humans; Male; Middle Aged; Models, Statistical; Movement; Muscle Rigidity; Parkinson Disease; Potentiometry; Range of Motion, Articular; Reproducibility of Results; Torque; Viscosity; Wrist Joint

Parkinsonian rigidity is characterized by an increased resistance of a joint to externally imposed motion that remains uniform with changing joint angle. Two candidate mechanisms are proposed for the uniformity of rigidity, involving neural-mediated excitation of shortening muscles, i.e., shortening reaction (SR), or inhibition of stretched muscles, i.e., stretch-induced inhibition (SII). To date, no study has addressed the roles of these two phenomena in rigidity. The purpose of this study was to differentiate these two phenomena, and to quantify the potential contribution of each to wrist joint moment in 17 patients with parkinsonian rigidity, in both Off- and On-medication states. Joint position, torque, and EMGs of selected muscles were collected during externally imposed flexion and extension motions. Moments of shortened and stretched muscles were estimated using a biomechanical model. Slopes of the estimated torque-angle curve were calculated for shortened and stretched muscles, separately. A mixed model ANOVA was performed to compare the contribution between the two mechanisms. During flexion, slopes were significantly (P = 0.003) smaller for SR than for SII, whereas during extension, slopes for SII were significantly (P = 0.003) smaller. Results showed that both SR and SII contributed to rigidity. Which mechanism predominates appeared to be associated with the direction of movement. The findings provide new insights into the biomechanical underpinnings of this common symptom in Parkinson's disease.

Topics: Aged; Analysis of Variance; Biomechanical Phenomena; Electromyography; Female; Humans; Male; Middle Aged; Muscle Contraction; Muscle Rigidity; Muscle, Skeletal; Parkinson Disease; Range of Motion, Articular; Reflex, Stretch; Torque; Wrist Joint

Muscle rigidity in PD (Parkinson's disease) patients represents an involuntary increase in muscle tone that stands out upon passive rotation of a joint. The pathophysiology of rigidity is still not well understood. We measured head-trunk torque in PD patients and normal controls during transient passive head rotations by means of servomotors under the instruction to the subjects to relax the neck muscles. We observed that rotation onset was followed by an initial rapid rise in resistive torque, similarly in both subject groups. It then leveled off or declined in controls. With PD patients, in contrast, the rise continued roughly proportional to head eccentricity almost until the end of the rotation. These observations led us to the hypothesis that the initial rise in torque represents reflexive head stabilization that normal subjects in the course of the rotational stimulus are able to suppress, whereas PD patients are less effective in doing so. The hypothesis was implemented into a dynamic control model of active and passive head rotation. Model simulations successfully reproduced the torque responses of normal subjects and PD patients in the present and previous studies.

Topics: Aged; Biomechanical Phenomena; Central Nervous System; Cervical Vertebrae; Disability Evaluation; Female; Head Movements; Humans; Male; Middle Aged; Models, Neurological; Muscle Rigidity; Neck Muscles; Neural Inhibition; Parkinson Disease; Postural Balance; Reflex, Abnormal; Rotation; Torque

Robotic manipulanda are extensively used in investigation of the motor control of human arm movements. They permit the application of translational forces to the arm based on its state and can be used to probe issues ranging from mechanisms of neural control to biomechanics. However, most current designs are optimized for studying either motor learning or stiffness. Even fewer include end-point torque control which is important for the simulation of objects and the study of tool use. Here we describe a modular, general purpose, two-dimensional planar manipulandum (vBOT) primarily optimized for dynamic learning paradigms. It employs a carbon fibre arm arranged as a parallelogram which is driven by motors via timing pulleys. The design minimizes the intrinsic dynamics of the manipulandum without active compensation. A novel variant of the design (WristBOT) can apply torques at the handle using an add-on cable drive mechanism. In a second variant (StiffBOT) a more rigid arm can be substituted and zero backlash belts can be used, making the StiffBOT more suitable for the study of stiffness. The three variants can be used with custom built display rigs, mounting, and air tables. We investigated the performance of the vBOT and its variants in terms of effective end-point mass, viscosity and stiffness. Finally we present an object manipulation task using the WristBOT. This demonstrates that subjects can perceive the orientation of the principal axis of an object based on haptic feedback arising from its rotational dynamics.

Topics: Arm; Biophysical Phenomena; Equipment Design; Humans; Learning; Motor Skills; Movement; Muscle Rigidity; Muscle, Skeletal; Range of Motion, Articular; Robotics; Torque

To examine the correlation between rigidity and interaction of stretch reflex and shortening reaction during passive movements of the wrist and to compare this correlation with that between rigidity and stretch reflex alone.. Twelve subjects with Parkinson's disease participated in the study in Off-medication and On-medication states. A servomotor imposed wrist flexion and extension within +/-30 degrees at velocities 50 and 280 degrees/s, while joint torque and EMG of the wrist flexors and extensors were recorded. Rigidity was quantified by integrating torque with joint angle, i.e., objective rigidity (OR) score, for extension and flexion, respectively. The interaction between EMG responses was estimated by calculating a ratio of normalized EMG in stretched to shortened muscles for both movements.. The OR scores were more strongly correlated with the EMG ratios than with EMG of the stretched muscles alone. The strongest and significant correlation was found between the OR score and EMG ratio during the extension at high velocity in the Off-medication (r=0.792, p=0.002).. Both stretch reflex and shortening reaction are important determinants of rigidity.. Study findings provide new insight into mechanistic descriptions of rigidity and have implications for development and evaluation of interventions.

Topics: Aged; Antiparkinson Agents; Dopamine Agents; Electromyography; Female; Humans; Male; Middle Aged; Muscle Contraction; Muscle Rigidity; Parkinson Disease; Range of Motion, Articular; Reflex, Stretch; Torque; Treatment Outcome; Wrist Joint

We propose a novel system that analyzes the components of rigidity in Parkinson's disease (PD) usually perceived by physicians, in a very simple and systematic way for routine clinical practice. Our system is composed of two compact force sensors, a gyroscope, and EMG surface electrodes. Muscle tone was assessed in 24 healthy elderly subjects and 27 PD patients by passive extension and flexion of the elbow joint with ramp-and-hold trajectory. Torque and angle data in the dynamic phase were used to calculate "elastic coefficients" in extension and flexion, and the mean value of torque in each dynamic phase at each joint angle (defined as "Bias") was also calculated. The muscle activity index in the static phase (EMG Index) was obtained for both biceps brachii (BB) and triceps brachii (TB) muscles. "Elastic coefficients," sum of the "difference of Bias" and "EMG Index" for BB all correlated well with UPDRS score. Based on our results, Parkinsonian rigidity consists of both an "elastic" component and a "difference of Bias" component, and neurologists may assess greater rigidity when either one or both components are high in value. The EMG index was useful for differentiating PD patients with slight rigidity from healthy elderly adults.

Topics: Aged; Aged, 80 and over; Bias; Biomechanical Phenomena; Case-Control Studies; Elasticity; Electromyography; Female; Humans; Male; Middle Aged; Muscle Contraction; Muscle Rigidity; Muscle, Skeletal; Parkinson Disease; Principal Component Analysis; Range of Motion, Articular; Statistics, Nonparametric; Torque

We aimed to develop an objective measurement to quantify trunk rigidity in patients with Parkinson's disease (PD), and to examine its reliability, validity and sensitivity in differentiating PD patients from control subjects. In Study 1, an isokinetic dynamometer was employed to assess trunk rigidity in 6 PD patients and 6 healthy controls. Passive trunk flexion and extension at 4 angular velocities were applied and resistive torques were recorded. Both work done and resistive peak torques to passive trunk flexion (Torque(PF)) and extension (Torque(PE)) were found to be highly reliable within a 2-day interval in PD patients and control subjects. In Study 2, trunk muscle tone was compared between 15 PD and 15 control subjects. Significantly higher muscle tone, as shown by increases in work done, and in Torque(PF) and Torque(PE )at higher movement speeds, was found in PD patients. Within each subject group, resistive trunk muscle tone was found to increase with increasing velocity of passive movement, but the extent of increase was greater in PD patients. Our results thus suggest that the objective method developed by us was reliable and could differentiate trunk rigidity in PD patients from that of healthy subjects.

Topics: Aged; Biomechanical Phenomena; Case-Control Studies; Electromyography; Female; Humans; Male; Middle Aged; Muscle Contraction; Muscle Rigidity; Muscle, Skeletal; Parkinsonian Disorders; Physical and Rehabilitation Medicine; Posture; Range of Motion, Articular; Reproducibility of Results; Sensitivity and Specificity; Severity of Illness Index; Torque

A cardinal feature of Parkinson's disease (PD) is muscle hypertonicity, i.e. rigidity. Little is known about the axial tone in PD or the relation of hypertonia to functional impairment. We quantified axial rigidity to assess its relation to motor symptoms as measured by UPDRS and determine whether rigidity is affected by levodopa treatment. Axial rigidity was measured in 12 PD and 14 age-matched controls by directly measuring torsional resistance of the longitudinal axis to twisting (+/-10 degrees ). Feet were rotated relative to fixed hips (Hip Tone) or feet and hips were rotated relative to fixed shoulders (Trunk Tone). To assess tonic activity only, low constant velocity rotation (1 degrees /s) and low acceleration (<12 degrees /s(2)) were used to avoid eliciting phasic sensorimotor responses. Subjects stood during testing without changing body orientation relative to gravity. Body parts fixed against rotation could translate laterally within the boundaries of normal postural sway, but could not rotate. PD OFF-medication had higher axial rigidity (p<0.05) in hips (5.07 N m) and trunk (5.30 N m) than controls (3.51 N m and 4.46 N m, respectively), which did not change with levodopa (p>0.10). Hip-to-trunk torque ratio was greater in PD than controls (p<0.05) and unchanged by levodopa (p=0.28). UPDRS scores were significantly correlated with hip rigidity for PD OFF-medication (r values=0.73, p<0.05). Torsional resistance to clockwise versus counter-clockwise axial rotation was more asymmetrical in PD than controls (p<0.05), however, there was no correspondence between direction of axial asymmetry and side of disease onset. In conclusion, these findings concerning hypertonicity may underlie functional impairments of posture and locomotion in PD. The absence of a levodopa effect on axial tone suggests that axial and appendicular tones are controlled by separate neural circuits.

Topics: Abdomen; Acceleration; Aged; Antiparkinson Agents; Female; Hip; Humans; Levodopa; Male; Middle Aged; Muscle Hypertonia; Muscle Rigidity; Parkinson Disease; Posture; Rotation; Severity of Illness Index; Thorax; Torque

Rigidity in Parkinson's disease (PD) is defined as an increased resistance to passive movement of a joint. The plastic-type rigidity is uniform and constant throughout the entire range of motion, whereas the cogwheel-type rigidity is accompanied by tremor. Rigidity in PD has been understudied. Thus, its pathophysiological basis remains unclear. The purpose of the study is to examine neuromuscular/biomechanical properties of PD rigidity and to provide its physiological characteristics. We hypothesize that PD rigidity presents as a flattened trace of joint torque vs. angular position (torque-angle relation) of the wrist, because the forces generated by lengthening muscles are offset by activation of the antagonist, i.e. show "shortening reaction" (SR). Experiments were conducted on six PD subjects medication OFF and ON. PD severity was assessed based on the unified Parkinson's disease rating scale. Each subject sat on a chair and was instructed to relax, with the wrist coupled to the device. The servomotor applied constant velocity displacement to create wrist flexion/extension. Electromyographic (EMG) responses were monitored from wrist muscles, along with position, velocity and torque. EMG magnitudes were computed over the movement period. Slopes were derived from the torque-angle trace. Results showed that SRs were routinely recorded OFF medication, but substantially reduced ON medication. Due to the interaction of SR, torque-angle relation was flatter OFF medication and became steeper ON medication. Correlation analyses showed that a strong correlation (R=0.65) existed between SR and torque-angle slope OFF medication, exclusively. We suggest that SR may play an important role in mediating the mechanical features of PD rigidity.

Topics: Adult; Aged; Antiparkinson Agents; Biomechanical Phenomena; Electromyography; Female; Hand; Humans; Male; Middle Aged; Muscle Contraction; Muscle Rigidity; Muscle, Skeletal; Parkinson Disease; Reaction Time; Torque; Wrist

Topics: Acceleration; Elbow Joint; Humans; Isometric Contraction; Muscle Rigidity; Muscle Spasticity; Range of Motion, Articular; Reflex, Stretch; Stroke; Torque

To quantify velocity dependent and position related properties of increased muscle tone measured during a constant velocity stretch.. Elbow flexors were vertically stretched under four different velocities (40, 80, 120, and 160 degrees /s) through a 75 degrees range of motion in 12 patients with hemiparesis, 16 with parkinsonism, and 12 normal controls. From reactive torque measurement, a linear second order model was adopted to dissociate velocity dependent viscous and velocity independent elastic components. The averaged speed dependent reflex torque (ASRT)--defined as the deviation of measured torque from baseline torque--was used to quantify the viscous component of hypertonia. Velocity sensitivity of ASRT (VASRT) and segmented ASRT (SASRT), derived from the slope of the regression line among ASRT velocity plots and from segmentations of reactive torque, respectively, were used to differentiate the increased muscle tone of spasticity and rigidity.. ASRT and VASRT were significantly higher in both spasticity and rigidity than in normal controls. SASRT analysis showed three different position related patterns among spasticity, rigidity, and normal groups: spasticity showed progressively increasing muscle tension relative to position; rigidity showed increased (relative to the norm) but constant muscle tone over the entire stretch range; the normal control group showed a consistently low reactive torque over the entire range.. Velocity dependence analysis indicates that rigidity and spasticity have approximately equal velocity dependent properties. For differentiating these two types of hypertonia, position dependent properties my be employed.

Topics: Adult; Aged; Biomechanical Phenomena; Diagnosis, Differential; Elbow; Female; Humans; Male; Middle Aged; Muscle Rigidity; Muscle Spasticity; Muscle, Skeletal; Paresis; Parkinsonian Disorders; Posture; Torque

The clinical assessment of rigidity is influenced by a number of variables which limit the reproducibility of rating scores and the usefulness of comparisons between subjects. We evaluated an objective measure of rigidity which uses unpredictable but reproducible limb perturbations mimicking the waveform, rate, and amplitude of those used in the clinical examination; and evaluates total resistive force, thus avoiding assumptions about the relative influence of elastic, viscous, or inertial components of the measured resistive forces on the genesis of rigidity. We then used this measure to quantify the effects of an activation procedure on parkinsonian rigidity, because this forms an important but poorly understood part of the routine clinical examination. We studied 20 patients with a clinical diagnosis of Parkinson's disease and 10 age-matched control subjects. A torque motor was used to deliver reproducible, transient, sinusoidal perturbations varying between 1.0 and 1.5 Hz. To quantify rigidity, we calculated angular impulse scores, which reflect the relationship between change in total resistive torque and time. Angular impulse scores were compared with work scores, which have previously been found to correlate with clinical assessments of rigidity. All subjects were studied at rest and with activation. Angular impulse scores were more consistently correlated with rigidity and more clearly differentiated between patients and control subjects than work scores. Activation increased both clinical and objective rigidity scores; activated angular impulse scores ranged from approximately 100%-200% of resting values. When plotted against clinical rigidity scores, activated angular impulse scores lay on a continuum with resting values. We conclude that angular impulse is a valid objective measure of parkinsonian rigidity. Activation increases rigidity, but to varying degrees in different patients. To improve the sensitivity and reproducibility of clinical rigidity assessments, parkinsonian rating scales should include separate resting and activated scores.

Topics: Aged; Biomechanical Phenomena; Female; Humans; Male; Middle Aged; Motor Activity; Muscle Rigidity; Parkinson Disease; Range of Motion, Articular; Reference Values; Rest; Torque

Because a so-called mandibular whiplash injury requires the absence of short-latency jaw-closing reflexes in order to explain the postulated mechanism of injury (excessive jaw opening); the authors studied the presence and absence and more importantly, the kinematics (duration, displacement, velocity, acceleration) of monosynaptic and possibly, polysynaptic myotatic (stretch) reflexes in the jaw elevator muscles. In six healthy adults jaw jerk maneuvers were elicited through a brisk tap on the chin, and surface electromyography identified elevator reflexes while translational electrognathography identified the kinematics of the reflexes. The maneuvers were done while maintaining the rest position (3% MVC) and moderate clenching of the teeth (30% MVC). Electromyography was also used to identify phasic elevator excitations during a passive brisk neck extension maneuver. A sudden and unexpected elongation of the jaw elevators released autogenic reflex responses that, in conjunction with augmented tissue elasticity (stiffness), elevated the mandible into centric occlusion within approximately 150 milliseconds. In 86% of trials, the responses occurred regardless of the prevailing resting and clenching contractile activities. There was no evidence of a depressor force that consistently would and could anchor the mandible in a position of extreme or moderate depression, the theoretical linchpin of the mandibular whiplash injury. It was concluded that the mandibular locomotor system is very efficient in maintaining the rest and intercuspal positions of the mandible. This study found no evidence corroborating the mechanism claimed to release a so-called mandibular whiplash injury.

Topics: Acceleration; Adult; Analysis of Variance; Compressive Strength; Elasticity; Electromyography; Female; Humans; Isometric Contraction; Jaw Relation Record; Male; Mandible; Masticatory Muscles; Movement; Muscle Rigidity; Neck Muscles; Reflex, Monosynaptic; Reflex, Stretch; Signal Processing, Computer-Assisted; Torque; Whiplash Injuries