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PubMed1990

Evaluation of shoulder movement as a command control source.

The purpose of this study was to evaluate the use of scapular shoulder movement as a command control source. The focus of this study was on the evaluation of movement signals from quadriplegic subjects as well as on the processing of these signals for use as command inputs to a functional neuromuscular stimulation (FNS) hand-grasp system. The shoulder movement of three C5-level quadriplegic and nine normal subjects was studied using externally mounted two-degree-of-freedom transducers overlying the sternum and clavicles. The C5-level quadriplegic subjects tested had a considerably poorer range of motion than the normal subjects. The range of motion was greatest in elevation but was coupled with a significant component of retraction. The vertical command resolution of the quadriplegic subjects ranged from eight to 13 command levels, whereas the horizontal range contained four or fewer command levels. Normal subjects were able to produce 26 to 79 command levels along the vertical axis and 18 to 85 along the horizontal axis. Subjects were able to maintain a static command level to within several percent of their range in trials lasting from 10 to 30 s. The quadriplegic subjects performed poorly in tasks where they were required to move to a point along the horizontal or vertical central axis and then along the opposite axis. The normal subjects were readily able to perform these tasks. The interference with the command signal due to movement of the opposite extremity was significant, with a maximum error ranging between 25 and 86% along the vertical axis and between 38 and 105% along the horizontal axis. Rise time and normalized velocity (velocity divided by the size of the movement) were found to be suitable for distinguishing different types of shoulder movements independent of the size of the movement. Shoulder movement in quadriplegics is suitable as a command control source for a FNS hand-grasp system requiring one proportional command signal and at least one logical command signal with appropriate processing of the signals. The available transducers are cosmetically acceptable and are easy to don and doff. Use of shoulder movement as a command control source does not interfere with other activities of the user such as eating or talking. Shoulder movement also provides a command control source that is easy for the user to learn and provides some feedback to the user through shoulder proprioception.

Adult↗
PubMed2006

Coordinative structure of manipulative hand-movements facilitates their recognition.

Manipulative hand movements involve coordinated movements of the fingers to manipulate an object within the hand, and are classified as either simultaneous or sequential. Simultaneous hand movements are characterized by single coordinated patterns of digit movements, while sequential hand movements involve sequences of such patterns. Here, we investigate the extent of the coordination among 15 hand-joints during simultaneous hand movements, and demonstrate that it leads to a concise representation that facilitates movement recognition. Principal component analysis (PCA), performed in the 15-dimensional (15-D) joint-space, indicates that the first principal-component captures more than 98% of the variability in individual hand movements. Consequently, the first principal direction provides a 15-D feature-vector that describes the underlying-coordination and can be used for automatic recognition. We evaluated this recognition strategy on a set of nine simultaneous hand-movements using a database of six users, each performing six sessions. A dedicated classifier for each user resulted in recognition rates of 97.0 +/- 4.7% during testing, while a single generic classifier achieved 95.2 +/- 2.5% recognition rates. We conclude that the suggested feature-vector captures the invariant structure of simultaneous hand-movements, facilitates their recognition, and may provide insight into motor planning.

Artificial Intelligence↗
PubMed2004

Brain potentials and behavioral responses associated with attention to hard- and easy-to-discriminate passive knee joint movements.

We investigated event-related brain potentials (ERPs) to passive ramp movements of the knee joint. The knee movements were either attended or unattended and were either very easy or very hard to detect. We used special methods to ensure that movement only activated muscle spindle and joint receptors. The first movement-related ERP started 20 ms after movement onset, and had a contralateral maximum. This initial ERP did not differ as a function of attention and movement discriminability. Signal detection analysis of the behavioral data suggested that hard-to-detect movements could be discriminated above chance level, but were not reported because of a decision bias. At 60-100 ms, an ERP was observed that discriminated detected from undetected hard-to-detect movements. Starting at 80 ms, we found an ERP that was unique to movements that were attended and easy to detect. We discuss that (1) the initial ERP reflects activation of preconscious sensory processors, (2) the second ERP may reflect detection that fails to attract attention, and (3) the third ERP reflects active focusing of attention on the movement.

Adult↗
PubMed2001

Directional tuning of human forearm muscle afferents during voluntary wrist movements.

1. Single unit activity was recorded with the microneurography technique from sixteen spindle afferents and one Golgi tendon organ afferent originating from the forearm extensor muscles. Impulse rates were studied while subjects performed unobstructed aiming movements at the wrist in eight different directions 45 deg apart. In addition, similar imposed movements were performed while the subject was instructed to remain relaxed. Movement amplitudes were about 5 deg and the speed 10-30 deg x s(-1). Joint movements were translated to movements of a cursor on a monitor to provide visual feedback. 2. Individual spindle afferents modulated their activity over a number of targets, i.e. were broadly tuned, during these aiming movements. The preferred direction for a spindle afferent was the same during both passive and active movements, indicating that the fusimotor effects associated with active contractions had little or no effect on the direction of tuning. 3. The direction of tuning of individual spindle afferents could be predicted from the biomechanically inferred length changes of the parent muscle. Thus spindle afferents responded as stretch receptors, i.e. impulse rates increased with lengthening and decreased with shortening, in active as well as passive movements. 4. Spindles from muscles, which continuously counteracted gravity exhibited a stretch response and directional tuning during the phase of movement alone whereas their position sensitivity was poor. In contrast, spindle afferents from the muscles that had no or minimal antigravity role were directionally tuned during both the dynamic and the static phase of the aiming task and their position sensitivity was substantially higher. 5. In spite of the limited data base from three extensor muscles it could be demonstrated that wrist joint position was remarkably well encoded in the ensemble muscle spindle data. In some cases the ensemble muscle spindle data encoded the instantaneous trajectory of movement as well.

Adult↗
PubMed2004

Whole-body-vibration training increases knee-extension strength and speed of movement in older women.

OBJECTIVES: To investigate the effects of 24 weeks of whole-body-vibration (WBV) training on knee-extension strength and speed of movement and on counter-movement jump performance in older women. DESIGN: A randomized, controlled trial. SETTING: Exercise Physiology and Biomechanics Laboratory, Leuven, Belgium. PARTICIPANTS: Eighty-nine postmenopausal women, off hormone replacement therapy, aged 58 to 74, were randomly assigned to a WBV group (n=30), a resistance-training group (RES, n=30), or a control group (n=29). INTERVENTION: The WBV group and the RES group trained three times a week for 24 weeks. The WBV group performed unloaded static and dynamic knee-extensor exercises on a vibration platform, which provokes reflexive muscle activity. The RES group trained knee-extensors by performing dynamic leg-press and leg-extension exercises increasing from low (20 repetitions maximum (RM)) to high (8RM) resistance. The control group did not participate in any training. MEASUREMENTS: Pre-, mid- (12 weeks), and post- (24 weeks) isometric strength and dynamic strength of knee extensors were measured using a motor-driven dynamometer. Speed of movement of knee extension was assessed using an external resistance equivalent to 1%, 20%, 40%, and 60% of isometric maximum. Counter-movement jump performance was determined using a contact mat. RESULTS: Isometric and dynamic knee extensor strength increased significantly (P<.001) in the WBV group (mean+/-standard error 15.0+/-2.1% and 16.1+/-3.1%, respectively) and the RES group (18.4+/-2.8% and 13.9+/-2.7%, respectively) after 24 weeks of training, with the training effects not significantly different between the groups (P=.558). Speed of movement of knee extension significantly increased at low resistance (1% or 20% of isometric maximum) in the WBV group only (7.4+/-1.8% and 6.3+/-2.0%, respectively) after 24 weeks of training, with no significant differences in training effect between the WBV and the RES groups (P=.391; P=.142). Counter-movement jump height enhanced significantly (P<.001) in the WBV group (19.4+/-2.8%) and the RES group (12.9+/-2.9%) after 24 weeks of training. Most of the gain in knee-extension strength and speed of movement and in counter-movement jump performance had been realized after 12 weeks of training. CONCLUSION: WBV is a suitable training method and is as efficient as conventional RES training to improve knee-extension strength and speed of movement and counter-movement jump performance in older women. As previously shown in young women, it is suggested that the strength gain in older women is mainly due to the vibration stimulus and not only to the unloaded exercises performed on the WBV platform.

Aged↗
PubMed1983

Peripheral control of the cat's step cycle. II. Entrainment of the central pattern generators for locomotion by sinusoidal hip movements during "fictive locomotion.".

Acute low spinal and curarized cats injected with noradrenergic agonists i.v. can elicit an efferent burst pattern which can be recorded in muscle nerve filaments and can be referred to as "fictive locomotion". This study investigates the effect that feedback, arising from movements in the hip joint, can exert on the central network generating fictive locomotion. The central network is uncoupled from generating any active movements by curarization. The motor pattern could be entrained by applying sinusoidal hip movements, even when a very extensive denervation of the leg had been performed leaving only some of the muscles around the hip and the hip joint innervated. During flexion movements, efferents to different flexor muscles became active and during movements in the reverse direction (extension), efferents to extensors were active. With an increasing movement frequency the onsets of both flexor and extensor bursts were delayed in the movement cycle. The duration of the extensor bursts varied markedly with the movement cycle, whereas pure flexors changed less in burst duration. The frequency within which the efferent burst activity was entrained in a strict 1:1 relation to the movement varied between 5 to 70% above and below the resting burst period. In preparations with a narrow 1:1 range, a "relative coordination" was encountered outside this range. The flexor burst duration was in these cases dependent on where in the hip movement cycle the bursts appeared.

4-Aminopyridine↗
PubMed1985

Motor control of voluntary trunk movements in standing.

The pattern of activity in different trunk muscles during voluntary trunk movements was studied in the standing position in man. The electromyographic activity from ventral and dorsal trunk muscles on the left and right sides were recorded together with the movements in the sagittal and frontal planes (Selspot optoelectronic system). Movement direction, amplitude, velocity and initial posture were varied. In all movements there was a basic pattern of alternation between antagonist muscle groups. Fast movements were initiated by a sharp burst of activity, whereas slow flexions and side bendings resulted from a decrease in antigravity muscle activity. Movement amplitude was related to the magnitude of the initiating burst, and also to the time of onset of antagonist muscle activity with a braking effect. The contribution of passive internal forces in the braking of a movement was indicated by the myoelectrical pattern of activity, particularly in slow large side bendings, where ipsilateral activity was present at the end of the movement. Sagittal movements starting at different initial trunk inclinations resulted in shifts in onset time and duration between antagonist muscles. The observed modifications are specific adaptations of the motor program to balance changes in mechanical conditions, such as angular acceleration, moment arm for the gravitational force, and intrinsic forces of active and passive structures surrounding the spine and pelvis. In conclusion, the present results demonstrate that trunk movements are generated and controlled by specific patterns of muscle coordination.

Adult↗
PubMed1987

Fast voluntary trunk flexion movements in standing: motor patterns.

The electromyographical (EMG) activity was studied during voluntary flexion movements of the trunk in erect standing man. The movements were performed at maximal velocity with successively increasing amplitude to cover the whole range of motion. The EMG activity was recorded from agonist-antagonist pairs of muscles at the ankle, knee, hip and trunk. The angular displacements at the corresponding joints were recorded using a Selspot optoelectronic system. The duration of initiating activity in prime movers (rectus abdominis and rectus femoris) as well as time to onset of activity in muscles braking the primary movement (erector spinae, gluteus maximus and hamstrings) were highly correlated with amplitude, duration, peak velocity and time to peak velocity of the movement (r = 0.59-0.91). The corresponding correlations for peak acceleration and deceleration of the movement were low (r = 0.03-0.38), indicating that acceleration and deceleration of a movement was not coded in the temporal aspects of the EMG. Onset of activity in rectus abdominis and rectus femoris as well as an early appearing burst of activity in vastus lateralis were invariant in relation to start of movement over the whole movement range. In the initial phase of a fast trunk flexion, activity in tibialis anterior appeared successively earlier with increasing movement amplitude. This resulted in a changed order of activation for the muscles from proximal to distal (rectus abdominis first) to distal to proximal (tibialis anterior first). Two different forms of associated postural adjustments are present during a fast trunk flexion, one early fast knee flexion and a later slower angle extension. Prior to knee flexion, no activity was recorded from muscles flexing at the knee implying that some other force must create a flexing torque around the knee. It is suggested that activity in rectus abdominis initiating the primary movement also initiates knee flexion through the upward pulling of pelvis. This would be possible since rectus femoris stabilizes the pelvis in relation to the leg, allowing the force in rectus abdominis to be transmitted below the hip joint and act extending around the ankle joint. However, when tibialis anterior is activated it stabilizes the shank which in turn will cause a knee flexion controlled by a lengthening contraction in vastus lateralis. During the subsequent ankle extension activity appears in lateral gastrocnemius and soleus causing the associated postural adjustment at the ankle. It can be concluded that activation of postural muscles prior to prime mover muscles is not always necessary.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1974

The forces generated at the human elbow joint in response to imposed sinusoidal movements of the forearm.

1. The mechanical resistance of the human forearm has been measured during imposed sinusoidal flexion-extension movements of the elbow joint.2. The force required to move the limb can be divided into components required to move the mass, and components required to overcome the resistance offered by elastic and frictional properties of the muscles and other soft tissues.3. When during a vigorous flexing effort the limb was subjected to a small amplitude sinusoidal movement each extension was followed by a considerable reflex contraction of the flexor muscles. At low frequencies of movement this reflex provided an added resistance to extension, but at 8-12 Hz the delay in the reflex pathway was such that the reflex response to extension occurred after the extension phase of the movement was over and during the subsequent flexion movement. The reflex activity then assisted the movement whereas at other frequencies it impeded it.4. The reflex response to movement increased as the subject exerted a greater flexing force.5. Small movements generated a relatively larger reflex response than big ones.6. Even with large amplitudes of movement when the reflex activity was relatively small, the limb resisted extension with a high level of stiffness; this was comparable with the short range stiffness of muscles in experimental animals.7. The fact that at some frequencies the reflex response assisted the movement implies that with appropriate loading the limb could undergo a self-sustaining oscillation at those frequencies.

Adolescent↗
PubMed1979

Ballistic flexion movements of the human thumb.

1. In response to an auditory stimulus normal subjects made ballistic flexion movements of the top joint of the thumb against a lever attached to the spindle of a low-inertia electric motor. 2. Electromyographic (e.m.g.) activity was recorded from pairs of fine wire electrodes inserted into flexor pollicis longus and extensor pollicis longus, respectively the sole flexor and extensor of the joint. 3. Movements of 5 degrees, 10 degrees and 20 degrees were made from initial angles of 10 degrees, 20 degrees and 30 degrees flexion against torques of 0.04, 0.08 and 0.16 Nm. 4. The e.m.g. activity initiating such movements was characterized by a 'triphasic' pattern of sequential bursts of activity in the agonist (flexor pollicis longus), then in the antagonist (extensor pollicis longus), and then in the agonist again. 5. The duration of the first agonist and first antagonist bursts ranged from about 50 to 90 ms and there was no significant change of burst length in the different mechanical conditions. 6. In movements of differing angular distance, the rectified and integrated e.m.g. activity of the first agonist burst could be correlated with the distance moved. The rectified and integrated e.m.g. activity of the first antagonist burst could not be correlated with the distance moved. 7. Responses of the muscles to perturbations either before or during the ballistic movements were studied. Current in the motor could be altered so to extend the thumb ('stretch'), to allow it to accelerate ('release'), or to prevent further movement ('halt'). 8. Suitably timed stretch increased the e.m.g. activity of the first agonist burst while release decreased it. 9. There was a small response of the agonist to stretch or halt timed to act during the interval between the first two agonist bursts; the major response was an augmentation of the second agonist burst. 10. Stretch, timed to act between the first two agonist bursts which released the antagonist, diminished the activity of the first antagonist burst while halt virtually eradicated it in all but one subject. Release, at this time, which stretched the antagonist, increased the activity of the first antagonist burst. 11. It is concluded that the individual components of a ballistic movement are relatively fixed in duration and the amount of e.m.g. activity is altered within this time interval to produce the different forces required for fast movements of different amplitude. 12. Both agonist and antagonist muscles remain under some feed-back control during the entire course of a ballistic movement, but the amount of influence of fedd-back depends on the supraspinal command signal and the changes in the spindle during the course of the movement.

Electromyography↗
PubMed1983

The function of the antagonist muscle during fast limb movements in man.

We have examined fast flexion movements of the human thumb and fast extension movements of the elbow over three different distances at a variety of speeds in order to elucidate the function of the antagonist muscle in these circumstances. All movements were of such a velocity that they showed the typical bi- or triphasic pattern of muscle activation in agonist and antagonist. Slower movements, with continuous agonist activity, were not analysed. For movements made through the same angle at different velocities, there was a linear relationship between the amount of antagonist activity needed to halt the movement and the peak velocity. However, the slope of this relationship was a function of the distance moved. Movements made through large angles showed less antagonist activity than those made through small angles at the same speed. The timing of the antagonist activity also changed as a function of both distance and speed. Fast, small movements showed earlier onset of antagonist activity than slow, large ones. Movements which were halted mechanically with the subject's prior knowledge had little or no antagonist activity, since it was no longer necessary in these conditions. The complexity of these relations indicates that the triphasic pattern of muscle activity underlying these movements can no longer be regarded as a simple immutable 'programme'. The size and timing of the bursts of muscle activity are subtly adjusted to the precise nature of the task.

Action Potentials↗
PubMed1983

Simple and complex spike activity of cerebellar Purkinje cells during active and passive movements in the awake monkey.

Two Rhesus monkeys (Macaca mulatta) were trained to pursue a target light signal by moving the hand at the wrist joint. Additionally, a d.c. motor could be attached to the lever in order to perform similar passive movements. During performance of the task, single Purkinje cells were recorded from the intermediate part of the cerebellar anterior lobe. Electromyographic activity of the flexor and extensor muscles of the forearm was recorded simultaneously. Passive hand movements evoked changes in the complex spike and simple spike discharge of Purkinje cell. The complex spike responded most sensitively to the beginning of the movement; the activity pattern had phasic character and could be related specifically to the movement direction. The simple spike response was usually weak and hence revealed-less specific relations. During active movements the simple spike frequency change was generally stronger than during passive movements and reached a maximum (or minimum) at the beginning of hand deflexion. The complex spike activity during active movements was characterized by a contrast between the time phases before and after the movement onset. In most of the cases, where a phase of increased activity stopped at the movement onset, the sensory feed-back signal seen during passive movements was cancelled. The possible consequences of the convergence of the complex and simple spike signal for the motor control function of the cerebellum are discussed.

Action Potentials↗
PubMed1988

Responses to passive movement of receptors in joint, skin and muscle of the human hand.

1. Microneurographic techniques were employed to record unitary activity from afferents associated with digital joints of six conscious human subjects. Of 120 single afferents sampled from the median and ulnar nerves at the wrist, eighteen (15%) were classified as joint afferents; the majority of the sample (72.5%) were of cutaneous origin, and 12.5% were from muscle spindles and tendon organs. 2. Of the eighteen joint afferents six were tonically active in the rest position of the hand. All except two were recruited or accelerated their background discharge during passive joint movement. Three tonically active afferents were responsive to passive movement throughout the physiological range. The majority of the afferents, including the other three tonically active units, responded only towards the limits of joint rotation. 3. As a group, the sample of joint afferents had a limited capacity to signal the direction of joint movement. Nine of the sixteen joint afferents sensitive to movement responded in two axes of angular displacement, and two responded in all three axes. In any one axis of rotation eight afferents were activated in both directions of movement. However, one afferent, associated with the interphalangeal joint of the thumb, responded uni-directionally throughout the physiological range of joint movement and was thereby capable of adequately encoding joint position and movement. 4. Twenty-one of twenty-nine slowly adapting and eleven of eighteen rapidly adapting cutaneous afferents tested were activated by joint movement, but only towards the limits of joint rotation; half of the thirty-two movement-sensitive afferents were bi-directionally responsive. Muscle spindle afferents responded to stresses applied to the joint only if the resulting passive movement stretched the parent muscle. 5. It is concluded that human joint afferents possess a very limited capacity to provide kinaesthetic information, and that this is likely to be of significance only when muscle spindle afferents cannot contribute to kinaesthesia.

Action Potentials↗
PubMed1990

Proprioceptive guidance of human voluntary wrist movements studied using muscle vibration.

1. The alterations in voluntary wrist extension and flexion movement trajectories induced by application of vibration to the tendon of flexor carpi radialis throughout the course of the movement, together with the associated EMG patterns, have been studied in normal human subjects. Both extension and flexion movements were routinely of a target amplitude of 30 deg and made against a torque load of 0.32 N m. Flexor tendon vibration consistently produced undershooting of voluntary extension movements. In contrast, voluntary flexion movements were relatively unaffected. 2. The degree of vibration-induced undershooting of 1 s voluntary extension movements was graded according to the amplitude (0.75, 1.0 and 1.5 mm) of flexor tendon vibration. 3. As flexor vibration was initiated progressively later (at greater angular thresholds) during the course of 1 s voluntary extension movements, and the period of vibration was proportionately reduced, so the degree of vibration-induced undershooting showed a corresponding decline. 4. Varying the torque loads (0.32, 0.65 and 0.97 N m) against which 1 s extension movements were made, and thereby the strength of voluntary extensor contraction, produced no systematic changes in the degree of flexor vibration-induced undershooting. 5. Analysis of EMG patterns recorded from wrist flexor and extensor muscles indicated that vibration-induced undershooting of extension movements resulted largely from a reduction in activity in the prime-mover rather than increased antagonist activity. The earliest reductions in extensor EMG commenced some 40 ms after the onset of vibration, i.e. well before voluntary reaction time; these initial responses were considered to be 'automatic' in nature. 6. These results support the view that the central nervous system utilizes proprioceptive information in the continuous regulation of moderately slow voluntary wrist movements. Proprioceptive sensory input from the passively lengthening antagonist muscle, presumably arising mainly from muscle spindle I a afferents, appears to be particularly important and to act mainly in the reciprocal control of the prime-mover.

Adult↗
PubMed2002

Initial arm muscle activation in a planar ballistic arm movement with varying external force directions: a simulation study.

It has been shown in previous research that the initial phase of EMG for a punching movement remained almost unchanged regardless of whether an external force was applied to the arm. The purpose of the present study was to explain this finding with the help of simulations. A two-dimensional model of the arm actuated by 6 Hill-type muscles was used to simulate a punching movement in the horizontal plane from a prescribed starting position with 90 elbow flexion. Input to the model was the stimulation of the muscles, and output were, among others, muscle forces and segmental accelerations. A genetic algorithm was used to determine the muscle onset times that minimized movement duration and targeting error. In a subsequent forward simulation, the optimized muscle onset times for an unloaded punching movement were superimposed on the isometric stimulation necessary to hold the arm in the starting position while an external force was applied to the arm. The resulting movement was only slightly different from the unloaded movement. It appeared that because of the low level of isometric muscle force prior to the movement, and the high level of stimulation during the movement, muscle force was increased at a rate that was almost independent of the prior force level. These results confirmed the suggestion that the initial phase of EMG in ballistic movements is more related to the rate of change of force than to the absolute force level. It is hypothesized that this may simplify the task of the nervous system in the choice of initial muscle activity in ballistic arm movements because no adjustments to varying external forces are required

Arm↗
PubMed1999

Proprioceptive regulation of voluntary ankle movements, demonstrated using muscle vibration, is impaired by Parkinson's disease.

OBJECTIVE: To test the hypothesis that the proprioceptive regulation of voluntary movement is disturbed by Parkinson's disease, the effects of experimental stimulation of proprioceptors, using muscle vibration, on the trajectories of voluntary dorsiflexion movements of the ankle joint were compared between parkinsonian and control subjects. METHODS: Twenty one patients with Parkinson's disease, on routine medication (levodopa in all but one), and an equal number of age matched, neurologically intact controls, were trained initially to make reproducible ankle dorsiflexion movements (20 degrees amplitude with a velocity of 9.7 degrees /s) following a visual "go" cue while movement trajectories were recorded goniometrically. During 50% of the experimental trials, vibration (105 Hz; 0.7 mm peak to peak) was applied to the Achilles tendon during the ankle movement to stimulate antagonist muscle spindles; vibrated and non-vibrated trials were interspersed randomly. Subjects' performance was assessed by measuring end point position-that is, the ankle angle attained 2 seconds after the visual "go" cue, from averaged (20 trials) trajectories. RESULTS: Statistical analysis of the end point amplitudes of movement showed that, whereas the amplitudes of non-vibrated movements did not differ significantly between patients with Parkinson's disease and controls, antagonist muscle vibration produced a highly significant reduction in the amplitudes of ankle dorsiflexion movements in both the patient and control groups. However, the extent of vibration induced undershooting produced in the patients with Parkinson's disease was significantly less than that in the controls; the mean vibrated/non-vibrated ratios were 0.86 and 0.54 for, respectively, the patient and control groups. CONCLUSIONS: The present finding of a reduction of vibration induced ankle movement errors in parkinsonian patients resembles qualitatively previous observations of wrist movements, and suggests that Parkinson's disease may produce a general impairment of proprioceptive guidance.

Aged↗
PubMed1988

Effect of active head movements about the pitch, roll, and yaw axes on human optokinetic afternystagmus.

Effects of active head movements about the pitch, roll, or yaw axes on horizontal optokinetic afternystagmas (OKAN) were examined in 16 subjects to test the hypothesis that otolith organ mediated activity induced by a change in head position can couple to the horizontal velocity storage in humans. Active head movements about the pitch axis, forwards or backwards, produced significant OKAN suppression. Pitch forward head movements exerted the strongest effect. Active head movements about the roll axis towards the right also produced OKAN suppression but only if the tilted position was sustained. No suppression was observed following sustained yaw. However, an unsustained yaw left movement after rightward drum rotation significantly enhanced OKAN. Sustained head movement trials did not significantly alter subsequent control trials. In contrast, unsustained movements about the pitch axis, which involve more complex interactions, exerted long-term effects on subsequent control trials. We conclude that otolith organ mediated activity arising from pitch or roll head movements couples to the horizontal velocity storage in humans, thereby suppressing ongoing OKAN. Activity arising from the horizontal canals during an unsustained yaw movement (observed mainly with yaw left), following drum rotation in a direction contralateral to the movement, may also couple to the velocity storage, resulting in increased activity instead of suppression.

Adolescent↗
PubMed2005

Signs of muscle thixotropy during human ballistic wrist joint movements.

A study was conducted on healthy subjects to determine whether voluntary ballistic wrist flexion movements are influenced by immediately preceding conditioning of the forearm muscles. Single rapid wrist flexion movements were made in response to an auditory "Go" signal. Rectified surface EMG was recorded from wrist flexors and extensors, and joint position was measured by a goniometer. The movements were preceded (2-3 s) by four different conditioning routines: 40-s rest (Rest), 10-s voluntary alternating wrist joint flexion and extension movements (Osc), and 10 s of 25 degrees weak isometric wrist extensor (Ext) or flexor contractions (Flex). When subjects made ballistic movements after Osc compared with Rest, peak velocity was higher (P = 0.02) and movement time shorter (P = 0.06), but there was no difference (P = 0.83) in motor reaction time (time between the onset of the first agonist burst and movement onset). If the movements were preceded by Ext compared with Flex, motor reaction time was longer (P = 0.01), indicating a longer electromechanical delay. There were no indications that postconditioning differences in agonist or antagonist muscle activity could explain the results. It was also demonstrated that, after Rest, peak velocity was lower (P < 0.01) for the first than for the second of a series of repetitive ballistic movements. The observations corresponded to results from passive experiments in which the median nerve was electrically stimulated. In conclusion, history-dependent (thixotropic) changes in skeletal muscle resistance seem to have implications for voluntary ballistic wrist movements. The study also provided evidence that muscle conditioning influences the central nervous reaction time preceding ballistic contractions.

Adult↗