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Biomedical subjects

M Woollacott

Publications and source records attributed to M Woollacott.

6 recordsLinked to original sources
PubMed1989

Visual, vestibular and somatosensory contributions to balance control in the older adult.

Age- and pathology-related changes in the relative contributions of visual and somatosensory inputs to dynamic balance control were evaluated. Young adults (mean age = 25, SD = 4) were compared to older adults (mean age = 68, SD = 5). Electromyographic responses were collected when subjects' balance was perturbed on a movable platform. The amounts of visual information and of somatosensory input at the ankle were manipulated. Muscle response latencies, losses of balance, and muscle sequencing were analyzed. Muscle response latencies did not differ across age groups. Loss of balance data indicated that older adults were less stable under conditions in which peripheral vision was occluded and ankle somatosensation was limited (only foveal vision and vestibular input remaining). Older adults showed more antagonist muscle activation and used muscle sequences not seen in young adults (e.g., hip strategy). These effects were exaggerated among subjects in whom borderline pathology had been diagnosed.

Accidental Falls↗
PubMed1988

Age-related changes in anticipatory postural adjustments associated with arm movements.

This study investigated the effects of age on the feedforward activation of postural muscles in advance of reaction time arm movements. Fifteen young (mean age 26 years) and 15 older (mean age 71 years) adult subjects were instructed to rapidly push or pull on a hand-held manipulandum. Postural muscle response onset latencies of the lower leg were significantly increased in the older adult group in three of the four conditions when compared to the young adult group. In addition, prime mover muscle response onset latencies of the upper arm showed a large, significant increase in older adults beyond that due to the slowing of the postural response. The results suggest two conclusions. The voluntary control system may be affected to a slightly greater degree with age resulting in slower voluntary movement in the elderly. Or, deterioration of the postural control system with age slows the speed of voluntary movement by delaying the onset of the voluntary muscle response.

Adult↗
PubMed1988

Response preparation and posture control. Neuromuscular changes in the older adult.

Experiments comparing the characteristics of neuromuscular responses underlying balance control in young and old adults have shown a number of differences between the two populations. Postural muscle response latencies of the ankle musculature activated by external threats to balance are slightly, but significantly, longer in the latter population. In addition, some aging subjects show a temporal reversal of proximal and distal muscle response onset in some trials. There is also a breakdown of the correlation of the amplitude of the muscle responses within a synergy in some of the older subjects tested. Older adults also exhibited cocontraction of agonist and antagonist muscles within a response synergy to a greater extent than young adults. This stiffening of the joints by antagonist cocontraction could be a compensation for the lack of the ability to fine-tune the postural responses to the same degree as the young adults. Analysis of sensory integration abilities showed an impairment in balance control under conditions of reduced or conflicting sensory information. When they were given inappropriate visual and somatosensory inputs, half of the older adults lost balance on the first trial. In most instances, however, the older adults were able to maintain balance during a second trial consisting of the same sensory stimuli. When visual cues were reduced by restricting the visual field to either central or peripheral visual cues, we found no difference in postural muscle response latencies. However, the aging adult group showed more losses of balance than the younger group with peripheral vision removed or with eyes closed. In addition, there was a strong correlation between the subjects that showed stronger deficits on an initial neurological exam and the number of times that balance was lost. Studies on changes in the linkage between postural and voluntary muscle interactions during voluntary arm movements in older adults indicate an increase in the latency of feed-forward activation of postural muscles. However, voluntary muscle response onset latencies show greater increases in the old compared to the young. This suggests that deterioration of the speed of activation of the postural control system is not the only factor that limits the speed of voluntary movement onset. Measurements have not yet been made on the amplitude regulation of feed-forward responses of postural muscles during a voluntary task. It may be that the regulation of the speed of activation of the two systems is less important than the fine tuning of the correlation of appropriate response amplitudes between the two systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗
PubMed1979

Organization of rapid responses to postural and locomotor-like perturbations of standing man.

This study has described the organization of EMG activities among the muscles of a standing subject's legs during rapid postural adjustments (95--120 ms latencies). Adjustments were elicited by the horizontal translation of both feet (causing antero-posterior sway), by the synchronous vertical displacement of both feet (causing changes in height) and by the reciprocal vertical displacement of the feet (causing changes in height) and by the reciprocal vertical displacement of the feet (causing a locomotor-like motion of the legs and lateral sway of the body). The resulting patterns of EMG activity were highly specific for each kind of displacement, and all subjects completely reorganized the pattern of activity from one form to another within the first trials, even immediately following unexpected stimulus changes. The organization of EMG activities during reciprocal vertical displacements was qualitatively quite similar to those observed during the comparable swing and stance phases of the locomotor step cycle; flexor muscles of the ankle and knee (those being shortened by the displacement) contracted in the upwardly displaced leg while extensor muscles were active in the downwardly displaced leg. This pattern was in marked contrast to the activation of lengthening muscles during synchronous vertical and antero-posterior sway displacements. Finally, electrical cutaneous stimulation of the dorsum of one foot during reciprocal vertical displacements always enhanced the EMG activity of the agonist leg muscles, in-phase with the vertical movement.

Ankle Joint↗