Center Of Pressure Measures Research Articles

Stability boundaries and lateral postural control in parkinson's disease.

Postural instability is a major problem in patients with Parkinson's disease (PD). We examined balance control in PD by using center of pressure (CP) variability and time-to-contact to investigate boundary relevant postural control behavior under quiet stance leaning conditions. Postural orientation was manipulated by having patients (n = 10) and healthy older controls (n = 7) lean forward and backward with varying degrees of lean on a force platform. The subjects were instructed to lean forward or backward (either halfway or as far as possible) without bending their hips or lifting their heels or toes off the ground. Time-to-contact of the CP with the geometric stability boundary defined by the feet as well as CP position and variability were analyzed. Medio-lateral CP variability was increased in the patients with PD. Medio-lateral average time-to-contact was decreased in the patients but not so in the anterior-posterior direction. In contrast to the CP variability, the medio-lateral variability of time-to-contact was lower in the patients. Patients as well as healthy older controls responded to lean manipulations with an increase in CP variability. Boundary relevant CP measures thus show clear changes in control strategies and confirm the role of lateral instability in PD.

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.

Stability criterion for controlling standing in able-bodied subjects

A new stability criterion that can be used to assess the standing condition of a subject from center of pressure (CoP) measurements is presented. This criterion can be applied, for example, to control a standing prosthesis, which should allow a paraplegic subject to stand up, sit down and stand safely without using hands for support. Experiments conducted with able-bodied subjects enabled us to establish a relationship between its stability and the subject's CoP position. Four CoP stability zones were identified: high preference, low preference, undesirable and unstable zones. The high preference zone is defined as the area where the CoP is found 99% of the time during quiet standing. The area where the CoP is found during the remaining 1% of the time is called the low preference zone. The undesirable zone is defined as the CoP area where the subject is forced to change posture in order to maintain balance, and the unstable zone is defined as the CoP area in which the subject is forced to step forward, backward or sideways to maintain stability. A general model of the proposed four stability zones was derived, which can be used to compute stability zones a priori for any subject and thus allows one to assess the subject's stability condition from the CoP measurements.

Postural control during stance in paraplegia: Effects of medially linked versus unlinked knee-ankle-foot orthoses

Objective: To investigate the effect of medially linking knee-ankle-foot orthoses (KAFOs) on postural stability and sway during (1) quiet standing and (2) functional activities for persons with spinal cord injury (SCI). Design: A randomized, mixed design, with the factors being activity (quiet standing and two function-mimicking tasks), SCI (present or not), and type of orthosis used in SCI group (linked or unlinked KAFO). Participants: Nine men with T5 to T12 paraplegia, 8 of whom had complete lesions and 1 with some sacral sparing (American Spinal Injury Association grade B) without proprioception, matched to 9 able-bodied men. Main Outcome Measures: Mean amplitude of sway and sway path in anteroposterior and mediolateral directions, derived from center of pressure measurements on a force platform. Results: All men with SCI were able to stand unsupported and perform function-mimicking activities in medially linked KAFOs; however, when wearing unlinked KAFOs only 5 could maintain balance during quiet stance and 3 could maintain balance during activity. Significant differences were found between linked and unlinked KAFOs; side-to-side mean amplitude of sway was less and sway path was greater for SCI subjects when they wore the linked KAFOs. Conclusion: Medial linkage of bilateral KAFOs provides an effective strategy to improve stability and increase postural control for persons with SCI, facilitating performance of functional activities during standing without upper limb support.

INCREASED SWAY AND REDUCED FUNCTION BUT NO FALLS IN ELDERLY WITH AND WITHOUT A VESTIBULAR DISORDER

1934 The goal of this study was to examine associations between measures of postural sway, and functional performance and self-efficiacy in 10 healthy young adults (Y, 24.6±0.73 yrs), 10 healthy older adults (H, 72.6±1.06), and 11 older adults (V, 69.1±2.22) with a vestibular disorder (perilymph fistula). Center of pressure (COP) data were collected using a force platform over 10, 30 s trials. Data on preferred walking speed (Pwalk, m/s), one leg balance time (1 Leg, s), timed get-up-and-go (Get Up, s), Berg balance test (Berg), isometric knee extensor strength and knee extensor muscle power (ExtP) and gait (GES) and falls efficacy were also recorded. MANOVA analysis revealed that there were no differences between Y and H on the 6 COP measures. Significant differences were observed between H and V on 3 of the 6 COP measures. There was little difference between the Y and H on any of the functional measures or the self-efficacy scales although H did exhibit reduced muscle power. Y performed markedly better than V on all the functional performance measures, gait efficacy scale, and muscle strength and power. COP measures (in particular medio-lateral range and variability, and average velocity) were correlated with the performance and efficiacy measures. Falls were assessed retrospectively. No subject in this study reported a fall within the previous 2 years. Despite marked increases in postural sway, functional decline, and lower self efficacy, older adults with a vestibular disorder had adapted their behavior to cope with a disorder that resulted in severely disturbed balance and vertigo. (Table)Table

Comparison of an in-shoe pressure measurement device to a force plate: Concurrent validity of center of pressure measurements

Comparison of an in-shoe pressure measurement device to a force plate: Concurrent validity of center of pressure measurements

Foot type: Determinant of static and dynamic foot function

Centre of pressure (COP), plantar pressure (PP), and plantar-flexion isometric strength (PFisom) are often examined in relation to postural control and gait.Our aim was to systematically review and quality appraise articles addressing the reliability of COP and PP measures in static stance and PFisom measures.Three electronic databases (SCOPUS®, SportDISCUS™, and PubMed) were searched and supplemented by a manual search. Peer-reviewed original research on the reliability of COP, PP, and PFisom in healthy adults (≥18 years) was included. Quality appraisal was done according to the updated COnsensus-based Standards for the selection of health Measurement INstruments reliability checklist. Data regarding study characteristics, test protocols, outcome measures, and reliability metrics were extracted.Forty articles met inclusion and were assessed for their methodological quality. Only four articles (10%) obtained uppermost quality scores. From the reviewed studies, the most reliable measures were: COP sway area and path length; PP mean pressure, percentage body weight distribution, and contact area; and PFisom peak torque and force. Although these measures generally exhibited good-to-excellent relative reliability based on correlation coefficients, absolute reliability based on typical errors were not always optimal (variation > 10%). Literature on PP reliability was scarce (n = 2).Our findings highlight the need for better quality methodological reliability studies to be undertaken to make stronger inferences about the reliability of COP, PP, and PFisom measures. The most reliable measures based on the current review are: COP sway area and path length; PP mean pressure, percentage of body weight distribution, and contact area; and PFisom peak torque and peak force. These measures are the ones that should be selected preferentially in clinical settings, bearing in mind that their typical errors might be suboptimal despite exhibiting strong relative reliability.

Retest Reliability of Centre of Pressure Measures of Standing Balance in Healthy Older Women

Centre of pressure (COP) measurements have been frequently used in the evaluation of postural control, especially in the elderly. Despite this, the retest reliability of these measures has not been well investigated in this age group. This study investigated the retest reliability of COP measures using a force platform in 17 women with a mean age of 69.5 years. Results indicated low correlations between test occasions for static stance postures with Intra class Correlation Coefficients (ICCs) ranging between 0.27 and 0.55. In contrast, ICCs were high (between 0.81 and 0.92) for test conditions involving angular perturbation of the support surface. Investigation of test durations of 10 and 25 second length did not indicate any significant difference between these two test durations (p>0.05). The study also revealed no series effects using twelve consecutive 25 second tests on the force platform. These results support further investigation of dynamic standing balance in older women using the test protocol described in this study, including whether these tests are able to discriminate between fallers and non fallen, and their predictive validity.

Steadiness in one-legged stance: development of a reliable force-platform testing procedure.

Postural steadiness in one-legged stance has potential for evaluation of unilateral injuries and disorders, but any test protocol must be demonstrated to be both feasible and reliable. A testing protocol for using a force platform to measure steadiness in one-legged stance with eyes opened and eyes closed was successfully developed, and its within-session retest reliability was investigated in a group of 24 young, healthy subjects. Strategies were used to minimize the loss of data for trials in which the subjects incurred significant loss of balance from the one-legged position. The performance scores examined were the standard deviation of the three orthogonal force components and the two horizontal center of pressure (CP) coordinates averaged over four consecutive five-second trials. The retest coefficients for all test conditions were substantially improved compared with testing protocols reported earlier. Retest reliability was higher for performance scores based on force measures than for performance scores based on CP measures. The difference was statistically significant in two of the stances, with a similar trend in the other two stances. Further, factor analysis showed that force measures were the best predictors of steadiness in one-legged stance. Analysis of variance failed to detect any systematic effect for leg preference or laterality on steadiness in one-legged stance with eyes opened or eyes closed in the healthy subjects with no history of injury (p greater than .05). The test protocol described enables the development of clinical or experimental trials with repeated-measures design using the subject's nonaffected leg as a control.