SUMMARY1. The resonance of the relaxed wrist for flexion-extension movements in the horizontal plane has been investigated by using rhythmic torques generated by a printed motor.2. In the normal subject the resonant frequency of the wrist is ca. 2 Hz unless the torque is reduced below a certain critical value when the system is no longer linear and the resonant frequency rises.3. This critical torque level, and the damping are both less in women than men. 4. The resonant frequency is uninfluenced by surgical anaesthesia. 5. With added bias the increase of resonant frequency at low torques still occurs although the hand is now oscillating about a displaced mean position.6. It follows that the stiffening implied by this elevation of resonant frequency for small movements is neither the result of pre-stressing of the muscles nor of reflex activity.7. With velocity feed-back of appropriate polarity the system will oscillate spontaneously at its resonant frequency. If the peak driving torque is progressively reduced the resonant frequency increases abruptly, indicating that the system has stiffened.8. Perturbations delivered to the wrist may reduce its stiffness. The postural system is thixotropic with a 'memory time' of 1-2 s.9. The resonant frequency is elevated in voluntary stiffening.
SUMMARY Observations on wrist tremor have been made in the horizontal plane using a tremorograph of new design. A small tap to the hand gave rise to a decrementing series of oscillations at about 9 Hz; as these effects were seen in relaxed and in anaesthetised subjects they were not due to neural reflexes. With the fingers partially extended the spontaneous tremor increased markedly and taps again gave rise to a series of oscillations. Under these circumstances there was no modulation of the EMG. It is accordingly concluded that mechanical wrist resonance plays a major role in the forms of tremor studied. sought to investigate the response to gentle taps which are nonetheless sufficient to generate a disturbance which is larger than the prevailing tremor; much of this work involved a tremorograph of new design. This paper describes oscillations similar to those found by Lippold but which are not accompanied by synchronised EMG activity. Furthermore, we show that these oscillatory transients can occur in conditions in which all active muscular activity is suspended. The short range resonant passive behaviour of the wrist joint and associated structures is a new finding which calls for significant modification of current theories.
SUMMARY Equinus in hemiplegic children is multifactorial. In some cases it is due to a short muscle, in others to simple foot‐drop, tonic spasticity, rigidity, compensation for a short limb, fixed flexion contracture at the hip, dominantly inherited forefoot deformity, forefoot equinus secondary to chronic toe‐walking, or abnormalities of the visco‐elastic properties of the muscle, with true intramuscular contracture. This neurophysiological study confirms that hemiplegia in children is not a homogeneous condition. Some have tonic spasticity; some, although stiff, show electrical silence on stretching; some appear to have a short muscle, with no hypertonicity; and others have hypertonicity in relation to position (i. e. rigidity). A short muscle is not always associated with tonic spasticity with reciprocal inhibition. Weakness can occur without spasticity. Speed of movement of toes, ankle and hip is also significantly reduced. RÉSUMÉ Neurophysiologie de la fonction du membre infeieur chez l'enfant hémiplégique L'équin de l'enfant hémiplégique est multifactoriel. Dans quelques cas, il est dûà un muscle court, dans d'autres à une chute du pied, une spasticité tonique, une rigidité, une compensation de membre court, une rétraction fixée en flexion de la hanche, une déformation de l'avant‐pied d'origine génétique dominante, un équin de l'avant‐pied par marche chronique sur les orteils, ou à des anomalies dans les propriétés visco‐élastiques du muscle, avec rétraction intra‐musculaire vraie. Cette étude neuro‐physiologique confirme que l'hémiplégie infantile n'est pas une condition homogéne. Quelques unes présentent une spasticité tonique; quelques unes se traduisent par un silence électrique à l'étirement en dépil d'une raideur; quelques unes se traduisent par un muscle court sans hypertonicité; d'autres ont une hypertonicité en rapport avec la position (p. e. la rigidité). Un muscle court n'est pas toujours associéà une spasticité tonique avec inhibition réciproque. La faiblesse peut survenir sans spasticité. La vitesse des mouvements des orteils, de la cheville et de la hanche est également réduite de façon significative. ZUSAMMENFASSUNG Neurophysiologie der Funktion der unteren Extremität bei Kindern mit Hemiplegie Der Spitzfuß bei Kindern mit Hemiplegie ist multifactoriell. In einigen Fällen ist er bedingt durch eine Muskelverkürzung, bei anderen durch einen einfachen Fallfuß, tonische Spastik, Rigidität, Kompensation für ein verkürztes Bein, fixierte Beugekontraktur der Hüfte, dominant vererbte Fußmißbildung, Spitzfuß durch ständiges Laufen auf den Zehen oder Anomalien der viskoelastischen Eigenschaften des Muskels mit intramuskulärer Kontraktur. Diese neurophysiologische Studie zeigt, daß die Hemiplegie bei Kindern keinen einheitlichen Charakter hat. Einige haben eine tonische Spastik; einige, obwohl starr, zeigen beim Strecken keine elektrische Reaktion; einige scheinen eine Muskelverkürzung ohne Tonuserhöhung zu haben; andere haben eine lageabhängige Hypertonic (Rigidität). Eine Muskelverkürrung ist nicht im...
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