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Biomedical subjects

H Hirschfeld

Publications and source records attributed to H Hirschfeld.

6 recordsLinked to original sources
PubMed1992

Development of anticipatory postural adjustments during locomotion in children.

1. Anticipatory postural adjustments were studied in children (6-14 yr of age) walking on a treadmill while pulling a handle. Electromyographs (EMGs) and movements were recorded from the left arm and leg. 2. Postural activity in the leg muscles preceded voluntary arm muscle activity in all age groups, including the youngest children (6 yr of age). The latency to both leg and arm muscle activity, from a triggering audio signal, decreased with age. 3. In older children the latency to both voluntary and postural activity was influenced by the phase of the step cycle. The shortest latency to the first activated postural muscle occurred during single support phase in combination with a long latency to arm muscle activity. 4. In the youngest children, there was no phase-dependent modulation of the latency to the activation of the postural muscles. The voluntary activity was delayed during the beginning of the support phase resulting in a long delay between leg and arm muscle activity. 5. The postural muscle activation pattern was modified in a phase-dependent manner in all children. Lateral gastrocnemius (LG) and hamstring muscles (HAM) were activated during the early support phase, whereas tibialis anterior (TA) and quadriceps (Q) muscles were activated during the late support phase and during the swing phase. However, in the 6-yr-old children, LG was also activated in the swing phase. LG was activated before the HAM activity in the youngest children but after HAM in 14-yr-old children and adults. 6. The occurrence of LG activity in postural responses before heel strike suggests an immature (nonplantigrade) gating of postural activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Myotatic reflex development in normal children and children with cerebral palsy.

Neonatal neuronal exuberance and its retention following neonatal brain damage have been demonstrated in a number of species but not in humans. The purpose of the present ongoing study is to determine if there is any evidence of neonatal neuronal exuberance and its retention following damage to the CNS in the human. Of equal concern is the determination of the neurological mechanisms underlying abnormal movement and reflex development in children with cerebral palsy.

Achilles Tendon↗
PubMed1991

The development of independent walking in children with cerebral palsy.

Electromyographic and kinematic data were collected during treadmill locomotion by normal infants and infants with cerebral palsy. Locomotor patterns of the infants with cerebral palsy were similar to those of normal infants during the stage of supported locomotion, but as they matured, some of the characteristics of the infant stepping pattern, such as synchronous muscle activity with excessive muscular co-contraction and short-latency reflexes at foot contact, were retained. The normal plantigrade features of adult gait did not develop in these children.

Brain↗
PubMed1991

Phase-dependent modulations of anticipatory postural activity during human locomotion.

1. The ability of the CNS to coordinate several motor tasks was studied in humans walking on a treadmill while pulling on a handle. Subjects were instructed to respond to an audio signal that was presented in different phases of the step cycle. Electromyograph (EMG) and movements were recorded from the left arm and leg. 2. The activity of the arm muscle was preceded by postural activity in the leg muscles. The pattern of the anticipatory postural activity differed in the various phases of the step cycle. Lateral gastrocnemius and hamstring muscles were activated during responses occurring in the early support phase whereas tibialis anterior and quadriceps muscles were activated when the pull was exerted during the late support phase and during the swing phase. In the middle of the support phase the combination of both muscle activity was present. 3. The temporal sequencing and the spatial distribution of the anticipatory muscle activity changed gradually. Early during the support phase the hamstring muscles were activated before the gastrocnemius muscle, whereas the order was reversed during midstance. The EMG amplitude of the hamstring and gastrocnemius muscles was largest in the beginning of the support phase and then gradually decreased, whereas the amplitude of the tibialis anterior and quadriceps muscles increased during the later parts of the support phase. 4. The anticipatory responses to pulls exerted during the first part of the support phase reduced the ankle flexion during the single support phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1990

Deficits in reciprocal inhibition of children with cerebral palsy as revealed by H reflex testing.

Experiments were performed to determine whether spinal and supraspinal components of reciprocal inhibition (a neural mechanism responsible for the prevention of muscular co-ordination during voluntary movement) were present in groups of non-disabled children and children with cerebral palsy. Changes in the gastrocnemius-soleus H reflex were examined during voluntary dorsiflexion and plantarflexion of the ankle and during a vibration applied to the anterior tibial tendon. The results indicate that children with cerebral palsy have impairments in reciprocal inhibition, both before and during voluntary movement. These deficits, which involve damage to supraspinal centres, contribute to their inability to perform smooth, co-ordinated movements.

Adolescent↗