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Biomedical subjects

M Woollacott

Publications and source records attributed to M Woollacott.

16 recordsLinked to original sources
PubMed2002

The influence of a concurrent cognitive task on the compensatory stepping response to a perturbation in balance-impaired and healthy elders.

This study investigated the influence of a concurrent cognitive task on the compensatory stepping response in balance-impaired elders and the attentional demand of the stepping response. Kinetic, kinematic and neuromuscular measures of a forward recovery step were investigated in 15 young adults, 15 healthy elders and 13 balance-impaired elders in a single task (postural recovery only) and dual task (postural recovery and vocal reaction time task) situation. Results revealed that reaction times were longer in all subjects when performed concurrently with a compensatory step, they were longer for a step than an in-place response and longer for balance-impaired older adults compared with young adults. An interesting finding was that the latter group difference may be related to prioritization between the two tasks rather than attentional demand, as the older adults completed the step before the reaction time, whereas the young adults could perform both concurrently. Few differences in step characteristics were found between tasks, with the most notable being a delayed latency and reduced magnitude of the early automatic postural response in healthy and balance-impaired elders with a concurrent task.

Accidental Falls↗
PubMed2001

The development of balance control in children: comparisons of EMG and kinetic variables and chronological and developmental groupings.

This cross-sectional study examined electromyographic (EMG) and kinetic variables during reactive balance responses in children grouped according to developmental level as compared with chronological age. Purposes were to explore relationships between the two types of variables and the effectiveness of the two grouping methods. Forty-four children between 9 months and 10 years old were tested for reactive balance control on a moveable platform. Surface electrodes measured EMG activity in the gastrocnemius (GA), hamstrings (HA), paraspinals (PS), tibialis anterior (TA), quadriceps (QA), and abdominal (AB) muscles. Timing and distance of center-of-pressure (COP) movements and peak muscle torques at the ankle, knee, and hip were also examined. Significant relationships and group differences were found between postural muscle activity and both the torque generated in the lower limbs and the timing and distance of COP adjustments employed to restabilize balance. As postural muscle activity increased and became more coordinated in timing, peak torque at the ankle and hip also increased, while the distance of and time to complete COP readjustments decreased. Children in younger/developmentally lower groups had smaller-magnitude and less-synergic muscle activity, lower peak torques, longer times to restabilize the COP, and greater COP paths than older/higher developmental groupings. Grouping by developmental level produced more statistical differences than did grouping by age. The correspondence of GA, HA, and PS muscle activity with COP measures and joint peak torques confirms that these muscles are key contributors to the balance synergy correcting for induced forward sway. Additionally, developmental level appears to be a much better predictor of balance improvement than chronological age.

Age Factors↗
PubMed2001

The interacting effects of cognitive demand and recovery of postural stability in balance-impaired elderly persons.

BACKGROUND: Although postural recovery is attentionally demanding in healthy elderly persons, an inability to recover balance due to competition for attentional resources between the postural system and a second task could contribute to falls in older adults with poor balance. This study examined the attentional demands of balance recovery from a mild postural disturbance in balance-impaired elderly persons. A second purpose of this research was to determine the effect of performing a cognitive task on the recovery of balance in balance-impaired elderly persons. METHODS: Fifteen healthy older adults and 13 older adults with clinical balance impairment were exposed to balance disturbances by means of sudden movement of a platform on which they stood. A dual-task paradigm where postural recovery served as the primary task and verbal reaction time to auditory tones served as the secondary task was used to assess attentional demand. To determine the effect of the cognitive task on postural recovery, kinetic, kinematic, and neuromuscular measures of a feet-in-place response were investigated. RESULTS: Balance recovery using a feet-in-place response was attentionally demanding in both groups of older adults and was more demanding in balance-impaired than in healthy elderly persons. With the concurrent performance of a cognitive task, balance-impaired elderly persons took longer to stabilize their center of pressure and regain balance than in a single task, while healthy elderly persons showed no change between conditions. In addition, only balance-impaired elderly individuals had a greater center-of-pressure resultant velocity during recovery in a dual-task compared with a single-task situation. CONCLUSIONS: The ability to recover balance using a feet-in-place response was more attentionally demanding in balance-impaired than in healthy elderly persons. The recovery of balance was also slower and less efficient in balance-impaired elderly persons when simultaneously performing a cognitive task, whereas the ability of healthy elderly individuals to recover was not influenced by concurrent task demands. This suggests that dual-task performance may contribute to postural instability and falls in balance-impaired elderly individuals.

Accidental Falls↗
PubMed2000

Development of postural adjustment during gait initiation: kinematic and EMG analysis.

The authors studied the development of postural adjustments associated with the initiation of gait in children by using kinematic and electromyographic (EMG) analysis. Participants (N = 28) included infants with 1-4 and 9-17 months of walking experience, children 4-5 years of age, and adults. Anticipatory postural adjustments (APA) were present in the youngest age groups, including a clear anticipatory lateral tilt of the pelvis and the stance leg, which enabled the child to unload the opposite leg shortly before its swing phase. An anticipatory activation of the hip abductor of the leg in stance phase prior to heel-off was found, suggesting pelvis stabilization. APA did not appear consistently until 4-5 years of age. A decrease in segmental oscillations occurred across the ages, indicating better control of intersegmental coordination in the frontal and sagittal planes during the postural phase of gait initiation. Young walkers presented APA involving movements of both the upper and the lower parts of the body, whereas, like adults, 4- to 5-year-olds were able to laterally shift only the pelvis and the stance leg. The oldest children and the adults also showed lower activation levels of hip and knee muscles but higher activation at the ankle level. Those kinematic and EMG results taken together suggest a clear developmental sequence from an en bloc operation of the body through an articulated operation with maturation, walking experience, or both.

Biomechanical Phenomena↗
PubMed2000

Attentional demands and postural control: the effect of sensory context.

BACKGROUND: This study used a dual task design to examine the effect of sensory context on postural stability during the concurrent performance of an attentionally demanding cognitive task in young and older adults with and without a history of imbalance and falls. METHODS: A choice reaction time auditory task was used to produce changes in attention during quiet stance in six different sensory conditions that changed the availability of accurate visual and somatosensory cues for postural control. Postural stability was quantified by using forceplate measures of center of pressure in 18 young adults, 18 healthy older adults, and 18 older adults with balance impairments and a history of recent falls. Reaction time and accuracy of verbal response to the auditory task were quantified by using a repeated measures analysis of variance. RESULTS: In young adults the auditory task did not affect postural stability in any of the sensory conditions. However, in the older adults the effect of the auditory task depended on sensory context. For healthy older adults, the addition of an auditory tone task significantly affected sway only when both visual and somatosensory cues for postural control were removed. In the balance-impaired older adults, the addition of the auditory task significantly affected postural stability in all sensory conditions. In addition, as sensory conditions became more difficult, older adults who had been able to maintain stability in a single task context lost balance when performing a secondary task. CONCLUSION: Results suggest that with aging, attentional demands for postural control increase as sensory information decreases. In addition, the inability to allocate sufficient attention to postural control under multitask conditions may be a contributing factor to imbalance and falls in some older adults.

Accidental Falls↗
PubMed2000

Predicting the probability for falls in community-dwelling older adults using the Timed Up & Go Test.

BACKGROUND AND PURPOSE: This study examined the sensitivity and specificity of the Timed Up & Go Test (TUG) under single-task versus dual-task conditions for identifying elderly individuals who are prone to falling. SUBJECTS: Fifteen older adults with no history of falls (mean age=78 years, SD=6, range=65-85) and 15 older adults with a history of 2 or more falls in the previous 6 months (mean age=86.2 years, SD=6, range=76-95) participated. METHODS: Time taken to complete the TUG under 3 conditions (TUG, TUG with a subtraction task [TUGcognitive], and TUG while carrying a full cup of water [TUGmanual]) was measured. A multivariate analysis of variance and discriminant function and logistic regression analyses were performed. RESULTS: The TUG was found to be a sensitive (sensitivity=87%) and specific (specificity=87%) measure for identifying elderly individuals who are prone to falls. For both groups of older adults, simultaneous performance of an additional task increased the time taken to complete the TUG, with the greatest effect in the older adults with a history of falls. The TUG scores with or without an additional task (cognitive or manual) were equivalent with respect to identifying fallers and nonfallers. CONCLUSION AND DISCUSSION: The results suggest that the TUG is a sensitive and specific measure for identifying community-dwelling adults who are at risk for falls. The ability to predict falls is not enhanced by adding a secondary task when performing the TUG.

Accidental Falls↗
PubMed1997

The effects of two types of cognitive tasks on postural stability in older adults with and without a history of falls.

BACKGROUND: This study used a dual task design to investigate the effects of two different types of cognitive tasks on stability (as measured by center of pressure displacement) in young vs older adults with and without a history of falls. METHODS: Two secondary cognitive tasks, a sentence completion and a visual perceptual matching task, were used to produce changes in attention during quiet stance under flat vs compliant surface conditions in 20 healthy young adults, 20 healthy older adults, and 20 older adults with a history of imbalance and falls. Postural stability was quantified using forceplate measures of center of pressure (COP). Speed and accuracy of verbal response on the cognitive tasks were also quantified. RESULTS: During the simultaneous performance of a cognitive and postural task, decrements in performance were found in the postural stability measures rather than the cognitive measures for all three groups. While no differences were found between the young adults and the older healthy adults on the firm surface, no task condition, when task complexity was increased (either through the introduction of a secondary cognitive task, or a more challenging postural condition such as standing on the compliant surface), significant differences in postural stability between the two groups became apparent. In contrast to the young and healthy older adults, postural stability in older adults with a history of falls was significantly affected by both cognitive tasks. CONCLUSION: Results suggest that when postural stability is impaired, even relatively simple cognitive tasks can further impact balance. Results further suggest that the allocation of attention during the performance of concurrent tasks is complex; depending on many factors including the nature of both the cognitive and postural task, the goal of the subject and the instructions.

Accidental Falls↗
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

Effects of gymnastics training on postural responses to stance perturbations.

The aim of the present experiment was twofold: (a) document the developmental course of postural responses to stance perturbations causing backward body sway and (b) investigate the plasticity of these responses by assessing the changes occurring in their organization as a result of gymnastics training. Fourteen untrained children (7 to 10 and 11 to 16 years old) and 15 age-matched gymnasts were tested on a movable platform. Four conditions were used: two-legged vs. one-legged stance x vision absent vs. present. Effects of age and training were assessed on the response latencies of eight muscles. Results showed no significant effect of age, but both stance and visual conditions affected the untrained subjects' response latencies. Wee found a significant effect of training on the response latency for the upper body muscles located on the frontal aspect of the body. This effect reflects an increase in gymnasts' response latencies as compared with controls'. Stance, but not vision, affected the responses of the trained subjects. Some implications of these results are discussed.

Journal Article↗
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↗
PubMed1987

Neuromuscular control of posture in the infant and child: is vision dominant?

This study explored the effects of vision and maturation on the characteristics of neuromuscular responses underlying balance control in both seated and standing children of five age groups (3 1/2-5 months, 8-14 months, 2-3 years, 4-6 years, and 7-10 years). A platform was used to unexpectedly disturb the child's balance in the anterior or posterior direction. Responses of the leg, trunk, and neck muscles were recorded using surface electromyograms. Vision was not required for the activation of these responses in any of the age groups tested. However, comparison of the muscle response latencies of standing children to posterior platform translation in the two visual conditions showed a significant reduction in latency for neck flexors in the 2- to 3-year-olds with vision removed and ann increase in the total number of monosynaptic reflexes. No reduction in latency was found in the older age groups. The hypothesis of a shift from an early long latency visual dominance to a shorter latency proprioceptive one during childhood is discussed. Postural control showed a cephalo-caudal developmental gradient with postural responses appearing first in the neck, then trunk, and finally, legs, as children developed from 3 to 14 months of age. A wide variety of response patterns was seen in the 3- to 5-month-olds, indicating that postural responses are not functional prior to experience with stabilizing the center of mass.

Journal Article↗
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↗