Biomedical subjects

Marjorie H Woollacott

Publications and source records attributed to Marjorie H Woollacott.

10 recordsLinked to original sources

PubMed2006

Attentional demands of postural control: the ability to selectively allocate information-processing resources.

Most studies have suggested the process of recovering body stability requires information-processing resources, but whether adults have the ability to selectively allocate resources to maintain balance is not known. Using a variable priority dual-task paradigm the present experiment investigated the extent to which young adults are able to shift attention between a postural task and a visual spatial memory task. Our results demonstrated a significant difference in verbal response time dependent on instructional set (focus on visual spatial memory versus postural task) but no difference in body sway measurement, indicating the ability of young adults to modulate visual spatial memory task, but not postural task focus. This suggests the existence of a hierarchy within attentional tasks with postural stability being a priority to stabilize gaze and head position.

Adult↗

PubMed2006

Training of balance under single- and dual-task conditions in older adults with balance impairment.

BACKGROUND AND PURPOSE: Traditionally, rehabilitation programs emphasize training balance under single-task conditions to improve balance and reduce risk for falls. The purpose of this case report is to describe 3 balance training approaches in older adults with impaired balance. CASE DESCRIPTIONS: Three patients were randomly assigned to 1 of 3 interventions: (1) single-task balance training, (2) dual-task training under a fixed-priority instructional set, and (3) dual-task training under a variable-priority instructional set. OUTCOMES: The patients who received balance training under dual-task conditions showed dual-task training benefits; these training benefits were maintained for 3 months. The patient who received variable-priority training showed improvement on novel dual tasks. DISCUSSION: Older adults may be able to improve their balance under dual-task conditions only following specific types of balance training. This case report gives insight on how this intervention might be combined with more traditional physical therapy intervention.

Accidental Falls↗

PubMed2005

Selective utilization of spatial working memory resources during stance posture.

While it has been shown that visual imagery tasks interfere with balance control, the neural mechanisms underlying the interference are unclear. Within a healthy young adult population, we employed a dual-task methodology to investigate the role of visual working memory in stance postural control. The employment of specific visual object and visual spatial working memory cognitive tasks facilitated the selective activation of cortically dissociated working memory resources. Challenging postural sets did not significantly impact object working memory performance, but clearly degraded performance on a spatial working memory task, suggesting that interactions between stance postural control and visual working memory are limited to the spatial domain. Results demonstrated no significant effect of the cognitive tasks upon postural stability.

Adult↗

PubMed2004

Postural response in older adults with different levels of functional balance capacity.

BACKGROUND AND AIMS: Aging is frequently accompanied by a deterioration in postural control, but it is not clear whether the primary contributor is increasing age or a progressive loss of functional balance capacity. The purpose of this study was to test the hypothesis that functional balance capacity contributes more than age to changes in postural response in the elderly. METHODS: The study considered 3 groups of healthy young, and functionally-stable and functionally-unstable older adults (N = 16 each group). Postural responses, including behavioral response patterns, joint angular displacement, displacement of the center of mass and center of pressure, and ground reaction forces, were induced and examined by submitting standing subjects to unexpected backward displacements in the surface supporting them. RESULTS: Functionally-stable older adults showed similar postural response patterns to those of young adults, whereas functionally-unstable older adults differed from young adults in the control of hip, trunk, shear force, and center of pressure trajectory during balance recovery. CONCLUSIONS: These findings support the hypothesis that changes in postural control in the elderly correlate with their functional balance capacity and are not just a matter of age.

Accidental Falls↗

PubMed2004

Bilateral accommodations to anterior cruciate ligament deficiency and surgery.

UNLABELLED: OBJECTIVE To determine bilateral lower extremity joint accommodations during gait in anterior cruciate ligament deficient subjects and uninjured controls. DESIGN: Gait testing of 10 chronic anterior cruciate ligament deficient subjects prior to and 3 months following reconstructive surgery, and 10 uninjured controls. BACKGROUND: It is possible that bilateral joint accommodations could occur as a result of anterior cruciate ligament injury and in response to surgical repair. Few studies have investigated bilateral joint accommodations to anterior cruciate ligament injury and there is little consistency in the reported results. METHODS: Bilateral lower extremity kinematic and kinetic data were collected from 12 walking trials and inverse dynamics calculations were made to estimate bilateral knee and hip joint angle, moment, and power patterns during the stance phase of gait. RESULTS: Control subjects exhibited asymmetrical hip but symmetrical knee joint moment and power patterns. In contrast, the anterior cruciate ligament deficient subjects exhibited symmetrical hip and asymmetrical knee joint moment and power patterns prior to and following reconstructive surgery. CONCLUSIONS: Gait asymmetry in healthy subjects should not be considered pathological. In addition, chronic anterior cruciate ligament injury results in joint specific, bilateral lower extremity accommodations in gait mechanics. These accommodations persist 3 months following surgical repair.

Adaptation, Physiological↗

PubMed2004

An emerging postural response: is control of the hip possible in the newly walking child?

Previous researchers have proposed that because of their slow muscle-response latencies, 1- to 2-year-old children are unable to control hip-dominant postural responses when responding to balance threats (G. McCollum & T. Leen, 1989). To test that proposition, the authors exposed 41 children to backward support-surface translations and recorded muscle activations and movement kinematics. Children between 10 months and 10 years of age stood on a platform that was unexpectedly moved. Passive hip-dominant responses were observed among the least experienced walkers. In contrast, older children produced an active response, signified by higher levels of abdominal and quadriceps muscle activity and accompanied by larger hip flexor torques. Greater success in withstanding large magnitudes of perturbations were associated with actively generated hip responses.

Anthropometry↗

PubMed2003

Gait perturbation response in chronic anterior cruciate ligament deficiency and repair.

OBJECTIVE: To determine how chronic anterior cruciate ligament deficient and surgically repaired subjects react to unexpected forward perturbations during gait as compared to healthy controls. DESIGN: Gait testing of 10 chronic anterior cruciate ligament deficient subjects prior to and three months following reconstructive surgery, and 10 uninjured controls. BACKGROUND: The ability of an anterior cruciate ligament injured individual to react and maintain equilibrium during gait perturbations is critical for the prevention of reinjury. No studies have investigated how these individuals respond to unexpected perturbations during normal gait. METHODS: An unexpected forward perturbation was induced upon heel strike using a force plate capable of translational movement. RESULTS: Prior to surgery, the anterior cruciate ligament subjects exhibited a greater knee extensor moment in response to the perturbation compared to healthy controls. Following surgery, the anterior cruciate ligament injured subjects exhibited a static knee position and a sustained knee extensor moment throughout stance in response to the perturbation as compared to controls. CONCLUSIONS: These data suggest that chronic anterior cruciate ligament deficient subjects rely heavily on knee extensor musculature to prevent collapse in response to an unexpected perturbation. This same reactive response was more pronounced 3 months following surgery. RELEVANCE: The results suggest that, prior to and following surgery, chronic anterior cruciate ligament injured subjects respond differently than healthy controls to an unexpected perturbation during gait. Anterior cruciate ligament injured or repaired subjects do not reduce or avoid vigorous contraction of the quadriceps muscles when responding to gait perturbations.

Adult↗

PubMed2002

Gait mechanics in chronic ACL deficiency and subsequent repair.

OBJECTIVE: To determine how normal gait patterns may change as a result of chronic anterior cruciate ligament deficiency and subsequent reconstructive surgery. DESIGN: Gait testing of 10 chronic anterior cruciate ligament deficient subjects prior to and 3 months following reconstructive surgery, and 10 uninjured controls. BACKGROUND: There is controversy whether persons with chronic anterior cruciate ligament deficiency develop a "quadriceps avoidance" pattern and how anterior cruciate ligament reconstructive surgery influences gait mechanics in these same individuals. METHODS: Gait analysis was employed to determine kinematic, kinetic, and muscle Electromyographic data. RESULTS: Prior to surgery, no anterior cruciate ligament deficient subject exhibited a quadriceps avoidance pattern. Following surgery, the subjects exhibited a significantly greater knee extensor moment during early stance as compared to the control group. Prior to and following surgery, anterior cruciate ligament deficient subjects demonstrated a significantly greater hip extensor moment possibly to reduce anterior tibial translation. CONCLUSIONS; These data suggest that (1) development of a quadriceps avoidance pattern is less common than previously reported, (2) anterior cruciate ligament deficient subjects accommodate through alterations of hip joint mechanics, (3) surgical repair significantly alters lower extremity gait patterns, and (4) re-establishment of pre-injury gait patterns takes longer than 3 months to occur. RELEVANCE: The results suggest that chronic anterior cruciate ligament deficient subjects do not exhibit a quadriceps avoidance gait pattern. Surgical intervention significantly alters lower extremity gait mechanics in a population that has accommodated to anterior cruciate ligament deficiency.

Adult↗

PubMed2002

Reactive balance adjustments to unexpected perturbations during human walking.

The purpose of this investigation was to determine the effect of unexpected forward perturbations (FP) during gait on lower extremity joint mechanics and muscle Electromyographic (EMG) patterns in healthy adults. The muscles surrounding the hip were found to be most important in maintaining control of the trunk and preventing collapse in response to the FP. Distinct lower extremity joint moment and power patterns were observed in response to the FP but an overall positive moment of support (M(s)) was maintained. Therefore, reactive balance control was a synchronized effort of the lower extremity joints to prevent collapse during the FP.

Adult↗

PubMed2002

Postural muscle responses following changing balance threats in young, stable older, and unstable older adults.

The authors determined the postural muscle response to support surface perturbations, in relation to aging and level of stability of 16 young adults and 32 older adults who were classified into stable (SOA) and unstable (UOA) groups on the basis of their functional balance abilities. Forward and backward support surface translations of various amplitudes and velocities were used so that postural responses of the standing adults could be elicited. The thigh and leg postural muscle responses were recorded with surface electromyography (EMG). The older groups had significantly longer onset latency in the anterior postural muscles, smaller integrated EMG in the posterior muscles, and greater extent of integrated EMG attenuation over time. The UOA showed longer onset latency in the gastrocnemius following slow backward perturbation and used a greater percentage of the functional capacity of the gastrocnemius muscle than the SOA did. Those findings indicate that the SOA and UOA had limited ability to adapt to changing balance threats; the UOA were more limited than the SOA. When designing balance training programs, therefore, therapists should consider the adult's level of functional stability.

Adult↗