Electromyographic study of the rigidospasticity of athetosis

Muscle Activity during Passive and Active Movements in Preterm and Full-Term Infants

Manifestation of muscle reactions at an early developmental stage may reflect the processes underlying the generation of appropriate muscle tone, which is also an integral part of all movements. In preterm infants, some aspects of muscular development may occur differently than in infants born at term. Here we evaluated early manifestations of muscle tone by measuring muscle responses to passive stretching (StR) and shortening (ShR) in both upper and lower limbs in preterm infants (at the corrected age from 0 weeks to 12 months), and compared them to those reported in our previous study on full-term infants. In a subgroup of participants, we also assessed spontaneous muscle activity during episodes of relatively large limb movements. The results showed very frequent StR and ShR, and also responses in muscles not being primarily stretched/shortened, in both preterm and full-term infants. A reduction of sensorimotor responses to muscle lengthening and shortening with age suggests a reduction in excitability and/or the acquisition of functionally appropriate muscle tone during the first year of life. The alterations of responses during passive and active movements in preterm infants were primarily seen in the early months, perhaps reflecting temporal changes in the excitability of the sensorimotor networks.

Muscle reaction to passive shortening in normal man

We have studied in 32 healthy subjects the EMG activity of biceps and triceps brachii, wrist flexors and wrist extensors, triceps surae and tibialis anterior, sterno-cleido-mastoideus (SCM) and splenius, during their passive shortening. A shortening reaction was observed more frequently in wrist extensors, SCM and tibialis anterior than in biceps and triceps brachii. The response appeared only when the joint reached a specific angle regardless of the starting point or the speed used to reach this position. During a muscle ischaemia which abolished the tendon reflex the reaction was not modified. During a joint ischaemia produced distal to the examined muscle its amplitude was strongly reduced. Our results support the hypothesis that joint receptors could play a role in its origin, perhaps through a long-loop reflex.

Measurement of involuntary arm movement in athetotic patients

Visual tracking tests have been used to obtain a quantified statistical description of the involuntary movements of the arm about the elbow joint in a group of patients suffering from athetoid cerebral palsy. Three separate components of involuntary activity can be recognized and it is possible that each may be a different physiological mechanism. First there are irregular movements which are represented by a continuous power spectrum which decreases with increasing frequency, reaching a negligible value between 2-3 Hz. The second component is a rhythmical low frequency movement which is indicated by a predominant peak in the power spectrum at a frequency of 0·3-0·6 Hz. The presence of this peak was predicted in a previous paper because of underdamping demonstrated in the closed loop voluntary control of movement in athetosis. The third component is the athetoid action tremor in which both agonist and antagonist muscle groups contract vigorously but asynchronously at a frequency of 1·5-4 Hz.

Comparison of the tonic stretch reflex in athetotic patients during rest and voluntary activity

An electromyographic technique was used to record the tonic stretch reflex (TSR) responses to passive sinusoidal stretching of biceps brachii muscle in athetotic patients. The TSR transmission characteristics measured while the patient was in a relaxed state were compared with those measured while the patient was voluntarily active. The resting TSR and action TSR were found to differ markedly. Sensitivity, pattern, duration, and timing of the TSR responses were all changed during voluntary activity. The results suggest that the TSR in athetosis is functionally reorganized by supraspinal influences during voluntary activity. It is proposed that athetoid movements and action tremor may be a manifestation of abnormal action TSR caused by faulty supra-spinal control during activity.

Quantitative study of the effect of L-dopa and phenoxybenzamine on the rigidity of Parkinson's disease

The static and dynamic components of the tonic stretch reflex and shortening reactions have been studied in biceps brachii, triceps, hamstrings, and quadriceps muscles of 19 patients with Parkinson's disease before and during L-dopa therapy. Clinical improvement during L-dopa administration correlated with a reduction in the dynamic component of the tonic stretch reflex in biceps, triceps, and quadriceps but not the hamstrings muscle, and with the static component of the tonic stretch reflex in biceps and triceps but not quadriceps and hamstrings muscles. The only shortening reaction consistently reduced during the L-dopa treatment period was the dynamic shortening reaction of the triceps muscle. The responses of the stretch reflexes to changes in muscle length were not altered by L-dopa therapy. In severely disabled patients the hamstrings and quadriceps stretch reflexes were maximal in a position of partial flexion of the knee joint and this response to muscle length was not altered in these patients despite a dramatic lessening of rigidity in some patients. Shortening reactions commonly remained in some patients after the stretch reflex of the antagonistic muscle was abolished by L-dopa therapy. The administration of phenoxybenzamine to patients being treated with L-dopa reduced the different components of rigidity more than L-dopa alone, and the responses were consistent with phenoxybenzamine suppressing predominantly the descending noradrenergic pathway.