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Biomedical subjects

H Forssberg

Publications and source records attributed to H Forssberg.

At least 19 recordsLinked to original sources
PubMed1992

Development of human precision grip. II. Anticipatory control of isometric forces targeted for object's weight.

The development of anticipatory control during lifts with the precision grip was examined in 100 children aged 1 to 15 years and in 15 adults. The children were instructed to lift an instrumented test object by using the precision grip between the thumb and index finger. The employed grip force, load force (vertical lifting force), vertical position and their corresponding time derivatives (i.e., grip and load force rates and acceleration) were recorded. The weight of the object was varied between trials to access the influence of the object's weight in the previous trial on the isometric force output. Already by the second year, children began to use information pertaining to the object's weight in the previous lift, i.e., they began to use an anticipatory control strategy. This occurred concomitant to the development of mainly bell shaped force rate profiles (Forssberg et al. 1991). The succeeding development of a more mature anticipatory control was gradual and adult-like capacity was not reached until 8-11 years of age.

Adolescent↗
PubMed1992

Development of human precision grip. III. Integration of visual size cues during the programming of isometric forces.

Recent evidence has shown that visual and haptical size information can be used by adults to estimate the weight of the object, forming the basis of the force programming during precision grip (Gordon et al. 1991a, b,). The present study examined the development of the capacity to use visual size information. In the first experiment, 30 children (age 1-7 years) and 10 adults performed a series of lifts with two boxes presented in an unpredictable order. The boxes were equal in weight but unequal in size and were attached to an instrumented grip handle which measured the employed grip force, load force, position and their corresponding time derivatives. The isometric force development was not influenced by the box size before the age of 3. However, the children aged 3 years and older demonstrated greater visual influences on the force programming than adults. To determine more precisely when children began to use visual size information, a second experiment in which the size and weight covaried was performed on 15 children. Children still did not use the size information during the force programming until the later half of the third year. It is concluded that this ability, probably involving associative transformations between the size and weight of objects, emerges around one year after anticipatory control based on somatosensory information pertaining to the weight of the object.

Adolescent↗
PubMed1992

Impaired anticipatory control of isometric forces during grasping by children with cerebral palsy.

The authors examined the force regulation during prehension of 12 children with cerebral palsy (CP) and an age-matched control group. The control group appropriately scaled the isometric force output in one force-rate pulse toward the weight of the previously lifted object, but children with CP exhibited stepwise increases in force in which the force amplitudes were not influenced by the object's weight. When the object was held in the air, most children with CP were able to modify their force output according to the object's weight, using sensory feedback, but their forces were more variable than those of the control group and less influenced by the object's weight. Although children with CP have disturbed sensory feedback--likely to lead to an indistinct internal representation of an object's physical properties--their main disability stems from impaired central co-ordination of motor activity.

Biomechanical Phenomena↗
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

[Functional development of the brain in the fetus and the infant].

Neuronal multiplication occurs mainly from the 10th to the 20th gestational weeks, after which probably no new nerve cells are formed, though neuronal arborisation and the formation and re-organisation of synapses continues until adulthood. An intriguing question is how the blueprint for the formation of about 100 billion nerve cells and their dendrites and synapses can be contained in the human genome. Environmental factors are probably crucially involved in the development of the brain, particularly from the later stages of gestation onwards. Somatosensory functions are developed at an early stage. The pain threshold is assumed to be lower in the fetus than in the adult. In man, general fetal movements appear from the 8th gestational week, and more complex movements such as sucking, swallowing and breathing during the 10th-12th gestational weeks. These movements are generated by neuronal networks, and seem to occur spontaneously without any sensory stimulation. At birth there is a general excitation of the infant, and the neonate is awake and aroused. Studies in rats have shown a multifold increase in noradrenaline turnover to occur in the brain stem at birth, which is assumed to be related to the arousal of the newborn. Recent studies have shown that there is a switch-on of various excitatory neuropeptide genes at birth, and an increase in noradrenaline in the locus coeruleus which is assumed to be the arousal centre.

Behavior↗
PubMed1991

Development of human precision grip. I: Basic coordination of force.

The coordination of manipulative forces was examined while children and adults repeatedly lifted a small object between the thumb and index finger. Grip force, load force (vertical lifting force), grip force rate and the vertical position of the test object were continuously measured. In adults, the force generation was highly automatized and was nearly invariant between trials. After a preload phase in which the grip was established, the grip and load forces increased in parallel under isometric conditions until the load force overcame the force of gravity and the object started to move. During this loading phase, the force rate profiles were essentially bell shaped and single peaked, suggesting that the force increases were programmed as one coordinated event. Children below the age of two exhibited a prolonged preload phase and a loading phase during which the grip and load forces did not increase in parallel. A major increase in grip force preceded the increase in load force, and at the start of the loading phase, the grip force was usually several Newtons (N). The force rate profiles were multi peaked with stepwise force increases most likely allowing peripheral feedback to play an important role in the control of the forces. After the age of two, the grip force increased less during the preload phase. The loading phase was more regularly characterized by a parallel increase of the grip force and load force and the duration of the various phases decreased. The older children programmed the forces in one force rate pulse indicating the emergence of an anticipatory strategy. Yet, the mature coordination of forces was not fully developed until several years later.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Visual size cues in the programming of manipulative forces during precision grip.

A size-weight illusion was used to examine the role of visual cues in the programming of manipulative forces during the lifting of test objects utilizing the precision grip. Three different boxes of equal weight and unequal size were lifted. These were equipped with an instrumented grip handle to measure the employed grip force, load force (vertical lifting force), force rates and vertical movement. All fifteen subjects participating in the study reported that the smallest box was the heaviest, which is consistent with size-weight illusion predictions. However, the rate of increase of the isometric grip and load forces initially during the lift, the peaks of the grip and load force and the vertical acceleration were all found to increase with the box size. Thus, despite the conscious perception indicating a heavier weight for the small object, the motor program was scaled for a lighter weight. Yet, no differences were found in grip force during the static phase of the lift, where weight related information was apparently available via sensory feedback. Previous studies have reported that the programming of the precision grip is based on somatosensory information gained during previous lifts (Johansson and Westling 1984, 1988a, b). The present study suggests that visual cues are integrated in the programming of manipulative forces during precision grip.

Adult↗
PubMed1991

The integration of haptically acquired size information in the programming of precision grip.

Recent evidence for the use of visual cues in the programming of the precision grip has been given by Gordon et al. (1991). Visually invoked size-related information influenced the physical forces used to produce a lift, even when it was not consistent with other sensory information. In the present study, blind-folded subjects were required to feel the size of an object by haptic exploration prior to lifting it. Two boxes of equal weight and unequal size were used for the lift objects and were attached to an instrumented (grip) handle. Grip force and load force, their rates, and the vertical movement of the object were measured. Most subjects reported that the small box was heavier, which is consistent with size-weight illusion predictions. However, peak grip force, grip force rate, peak load force, and load force rate were greater for the large box when the boxes were randomly presented, but not when the same boxes were lifted consecutively. If subjects did not feel the box prior to a lift, these parameters were scaled in between those normally employed for the large and small box. Most subjects apparently programmed the parallel increase of the grip and load force during the loading phase as one force rate pulse. This represented a "target strategy" in which an internal neural representation of the objects weight determined the actual target parameter (i.e. just enough force required to overcome gravity). The other subjects exhibited a slower stepwise increase in grip and load force rate. The subjects choosing this "probing strategy" did not scale the force parameters differently for the two boxes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Integration of sensory information during the programming of precision grip: comments on the contributions of size cues.

Evidence has recently been given by Gordon et al. (1991a, b) for the use of visually and haptically acquired information in the programming of lifts with the precision grip. The size-related information influences the development of manipulative forces prior to the lift-off, and the force output for larger objects is adjusted for a heavier weight even if the weight of the objects is kept the same. However, the size influences on the force output were small compared to the relative effects of the expected weight in previous trials (Johansson and Westling 1988). In the present study, both the size and weight of objects were changed between consecutive lifts to more fully determine the strength of visual size cues. During most trials, the size and weight covaried (i.e. the weight was proportional to the volume). However, in some trials, only the size was switched while the weight was kept the same to create a mismatch between the size and weight. The forces were still appropriately scaled towards an expected weight proportional to the volume of the object. It was concluded that visual size cues are highly purposeful. The effects were much larger than previously reported and were similar in magnitude to the effects based upon the expected weight. Thus, the small effects reported in the previous experiments may have been a result of conflicting "size-weight" information.

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

Basic co-ordination of manipulative forces of children with cerebral palsy.

The coordination of manipulatory forces during prehension was studied in 12 children with cerebral palsy (CP) and compared with that of controls. The results indicated that coupling of grip force and load force does not develop in children with CP. These children's force development increased in stages, with an early onset of excessive grip force. They did not use anticipatory control of the isometric force development during the load phase. Prolonged delays between successive phases indicated inefficient sensory feedback during the movement. The early onset of grip force and the over-all high force employment may compensate for the lack of anticipatory control and inefficient sensorimotor integration.

Cerebral Cortex↗
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↗
PubMed1991

[Functional development of the brain in the fetus and the newborn infant].

Neuronal multiplication occurs mainly from the 10th to the 20th gestational weeks, after which probably no new nerve cells are formed, though neuronal arborization and the formation and re-organisation of synapses continues until adulthood. An intriguing question is how the blueprint for the formation of about 100 billion nerve cells and their dendrites and synapses can be contained in the human genome. Environmental factors are probably crucially involved in the development of the brain, particularly from the later stages of gestation onwards. Somatosensory functions are developed at an early stage. The pain threshold is assumed to be lower in the fetus than in the adult. In man, general fetal movements appear from the 8th gestational week, and more complex movements such as sucking, swallowing and breathing during the 10th-12th gestational weeks. These movements are generated by neuronal networks, and seem to occur spontaneously without any sensory stimulation. At birth there is a general excitation of the infant, and the neonate is awake and aroused. Studies in rats have shown a multifold increase in noradrenaline turnover to occur in the brain stem at birth, which is assumed to be related to the arousal of the newborn. Recent studies have shown that there is a switch-on of an excitatory neuropeptide genes at birth, and an increase in noradrenaline in the locus coeruleus which is assumed to be the arousal centre.

Brain↗
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↗
PubMed1989

Rotational and translational movement features of the pelvis and thorax during adult human locomotion.

The kinematics of the pelvis and thorax are important in gait studies since their movement patterns are closely related to gait efficiency and 'smoothness' of locomotion. The purpose of this study was to identify features of normal gait patterns for later comparisons with pathological and developmental gait patterns. A two camera SELSPOT system interfaced with an HP1000 minicomputer was used to obtain three-dimensional kinematic/temporal data for the pelvis and thorax. Data from treadmill walking of eight adults were used for within subject (at different speeds) analyses. The analyses revealed a very complex pattern with a set of breakpoints which was consistent over all subjects. Some features were invariant over a range of walking speeds although the total range of motion changed considerably.

Adult↗