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At least 19 recordsLinked to original sources
PubMedDate not supplied

[Characteristics of the pressure center movement under upright posture regulation].

The hypothesis was put forward that, along with the regulation of mass center projection, the system of upright posture control stabilizes the deviation of pressure center from the position of the mass center projection. The regularities in the behavior of the trajectories of pressure center and mass center projection were analysed. Experimental evidence was obtained supporting the validity of the hypothesis. The structure of the control system that corresponds to the new understanding of the variables being regulated during the maintenance of vertical posture was considered.

Algorithms↗
PubMed2000

Intrasession reliability of the "center of pressure minus center of mass" variable of postural control in the healthy elderly.

OBJECTIVES: To estimate the intrasession reliability of a single measure of the biomechanical variable "center of pressure minus center of mass" (COP-COM) to determine, first, how many trials must be averaged to obtain a reliable measure of postural stability, and second, the minimal metrically detectable change of the COP-COM. PARTICIPANTS: Community-living, healthy, elderly people over 60 years of age (n = 7). DESIGN: Measurements were made in double leg stance, eyes-open condition. Nine successive trials, with rests between, were carried out for each subject. DATA ANALYSIS: Intraclass correlation coefficients (ICCs). MAIN OUTCOME MEASURE: The biomechanical variable COP-COM, which represents the distance between the center of pressure and the center of mass, was measured from two force platforms and three position sensors. RESULTS: The ICCs obtained for one measure of the COP-COM were .79 in the anterior-posterior (AP) direction and .69 in mediolateral (ML) direction. With four trials, the COP-COM variable is reliable at .94 in the AP direction and .90 in the ML direction. Minimal metrically detectable changes were .10 mm (AP) and .16 mm (ML). CONCLUSION: Using four repetitions of the COP-COM variable provides a reliable measurement of postural stability.

Aged↗
PubMed1991

[Photoelastic studies of the position of plantar pressure center and its changes at standing upright: analysis on Down syndrome].

With a photoelastic method, contact pressure patterns between foot and the floor surface were recorded, occasionally for one minute. The aim of this study is to evaluate the development or maturity of postural control. As a clinical model to be tested, Down syndrome characterized by marked muscular hypotonicity was chosen for quantitative analysis. The following results were obtained; (1) the center of contact pressure is shifted significantly forward in Down syndrome, (2) the position tends to move forward on the left side in both normal and Down syndrome groups, and (3) there was no distinctive laterality of weight loading on either side. Flaccidity of ankle joint movements such as abnormal eversion was indicated by a special parameter, which was obtained for the first time by this method.

Child↗
PubMed2002

Effect of center of pressure and trunk center of mass optimization methods on the analysis of whole body lifting mechanics.

OBJECTIVE: This study evaluates methods to optimize the trunk center of mass position, the center of pressure position, or both to minimize the difference between horizontal location of the whole body center of mass estimated by the model and center of pressure measured during static postures. DESIGN: Within subjects repeated measures. BACKGROUND: Methods to optimize the trunk center of mass position have been proposed in the past, but have not been fully evaluated nor have accounted for errors in the location of the center of pressure. Accurately determining these locations affects the understanding of the control of balance. METHODS: Six methods were compared using kinematic and force plate data from 22 subjects. Static postures resembling both leg and back lifting techniques were used to optimize the center of mass. A typical lifting movement was used to evaluate the effectiveness of the methods in reducing the difference between external moment and time derivative of the angular momentum. RESULTS: Optimization of the center of pressure had a statistically significant effect on reducing errors (P<0.05), whereas optimization of the trunk center of mass alone had not (P>0.05). CONCLUSIONS: Optimizing the center of pressure was simple and compensated for systematic errors introduced from the model and instrumentation. The addition of the center of mass optimization improved some results but added much complexity to the experimental procedures. RELEVANCE: Reducing errors in determining the relative position of the center of pressure and center of mass enhances the understanding of balance control as this relationship reflects the dynamic stability of the system.

Adult↗
PubMed1995

[Study of standing exactitude determined by the scatter of the center of pressure--study of standing exactitude by center of pressure].

In so far as stance is maintained during various activities, the center of pressure must be maintained with a certain area. This area is the range of the center of pressure. It is influenced by standing conditions and vision. In this study we used a force platform to measure the range of the center of pressure in 10 normal adults during maximal voluntary shifting from right to left, back and forth under 6 conditions (standing conditions: both legs apart, both legs together and standing on one leg; vision: eyes open and eyes closed). We also recorded the center of pressure while standing still for 30 seconds under the above 6 conditions. The scatter of the center of pressure and the range of the center of pressure were compared. Under easy standing conditions, the range of the center of pressure was very large and the center of pressure was concentrated in a small area. The more difficult the standing condition, the smaller the range of the center of pressure, and the wider the scatter of the center of pressure. Under very difficult standing conditions, the range of the center of pressure was almost as large as the area in which the center of pressure was scattered. Since the range of the center of pressure is closely connected with the scatter of the center of pressure, it may be possible to determine the accuracy of stance regulation by analyzing the range of the center of pressure and the scatter of the center of pressure.

Adult↗
PubMed1981

The center of pressure path in treated clubfeet.

The center of pressure paths of foot-floor contact were examined in detail in normal subjects and a group of 44 patients with treated clubfeet. The foot-floor contact areas were wide and the center of pressure paths more variable in clubfeet patients. The center of pressure paths did not always distinguish between normal and abnormal subjects nor between abnormal subjects with varying functional ratings. Foot prints are not sensitive enough to be a diagnostic aid and are of only limited application to the problem of evaluation of treatment of clubfoot deformity.

Adult↗
PubMed1997

Stochastic processes in postural center-of-pressure profiles.

The stochastic processes of postural center-of-pressure profiles were examined in 3- and 5-year-old children, young adult students (mean 20 years), and an elderly age group (mean 67 years). Subjects stood still in an upright bipedal stance on a force platform under vision and nonvision conditions. The time evolutionary properties of the center-of-pressure dynamic were examined using basic stochastic process models. The amount of motion of the center of pressure decreased with increments of age from 3 to 5 years to young adult but increased again in the elderly age group. The availability of vision decreased the amount of motion of the center of pressure in all groups except the 3-year-old group, where there was less motion of the center of pressure with no vision. The stochastic properties of the center-of-pressure dynamic were assessed using both a two-process, random-walk model of Collins and De Luca and an Ornstein-Uhlenbeck model that is linear and has displacement governed only by a single stiffness term in the random walk. The two-process open- and closed-loop model accounted for about 96% and the Ornstein-Uhlenbeck model 92% of the variance of the diffusion term. Diffusion parameters in both models showed that the data were correlated and that they varied with age in a fashion consistent with developmental accounts of the changing regulation of the degrees of freedom in action. The findings suggest that it is premature to consider the trajectory of the center-of-pressure as a two-process, open- and closed-loop random-walk model given that: (a) the linear Ornstein-Uhlenbeck dynamic equation with only two parameters accommodates almost as much of the variance of the random walk; and (b) the linkage of a discontinuity in the diffusion process with the transition of open- to closed-loop processes is poorly founded. It appears that the nature of the stochastic properties of the random walk of the center-of-pressure trajectory in quiet, upright standing remains to be elucidated.

Adult↗
PubMed2006

Generalizability of center of pressure measures of quiet standing.

Center of pressure (COP) measures are commonly used as indicators of balance and postural control. At present, there are no universally accepted standards in research investigating fluctuations in the COP with regard to the number of trials or the length of a given trial. The purpose of this study was to use the tools of Generalizability Theory (G-Theory) to investigate the reliability of COP measures of quiet standing and to establish an optimal measurement protocol. G-Theory provides a tool that allows us to break down the sources of variation, or facets, in a measurement procedure and ultimately design a protocol that provides optimal reliability. Fifteen participants completed 10 90-s trials with eyes open and closed. COP measures of anterior-posterior standard deviation (SD(AP)), medial-lateral SD (SD(ML)), average velocity (Vel), and 95% confidence ellipse area (Area) were calculated using the first 30, 60, and 90s of each trial. A G-study and follow-up D-studies were performed to estimate reliability coefficients (G-coefficients). The results of the G-Theory analysis suggest that these COP measures reached acceptable levels of reliability (G>or=0.70) with at least five 60s trials.

Adult↗
PubMed2000

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

The purpose of this study was to assess the concurrent validity of center of pressure (COP) measurements during walking, comparing the Parotec System (an in-shoe pressure measurement device) to an Advanced Mechanical Technology Inc. (AMTI) force plate. Pearson correlation coefficients comparing COP displacement in the medial-lateral (ML) and anterior-posterior (AP) direction calculated from the two systems were greater than 0.70 for 52/67 trials (78%) in the ML direction and were greater than 0.90 for 67/67 trials (100%) in the AP direction. The mean root mean square (RMS) error for COP displacement in the ML direction was 0.56+/-0.3 cm and in the AP direction was 1.37+/-0.59 cm. Overall, the Parotec System showed good correlation and small RMS errors when compared to the AMTI force plate. Additional analysis to investigate sources of error pointed to the methods used for calculating the position and orientation of the subject's foot on the force plate. Subsequent analysis to eliminate some of these errors, compared force calculated from the Parotec System and the AMTI plate and showed good to excellent correlation (>0.70) for 62/67 trials (93%). Additional data were collected that allowed for elimination of methodological errors. Again force calculated from the two systems was compared using Pearsons. These data showed excellent correlation (>0.90) for 20/20 trials (100%). This study provides evidence of the validity of the Parotec System for measuring COP during ambulation.

Adult↗
PubMed1999

Center of pressure and its theoretical relationship to foot pathology.

The measurement of center of pressure has been widely used in the evaluation of foot function. This article will describe center of pressure and indicate how it can be used to calculate moments about the joint axes of the foot. Various uses of center of pressure described in the literature will be examined. A model based on the use of the location of center of pressure relative to the location of the subtalar joint axis will be proposed as a theoretical explanation of selected foot pathologies and their treatment.

Biomechanical Phenomena↗
PubMedDate not supplied

Velocity of the center of pressure during walking.

The purpose of this study was to describe the velocity of the center of pressure during walking in a sample of young, healthy individuals. The velocity of the center of pressure was recorded in 60 subjects while they walked barefoot over a floor-mounted pressure platform. The results of this study indicate that the velocity of the center of pressure follows a predictable pattern during the stance phase of walking. Intraclass correlation coefficients calculated to measure between-trial reliability for specific parameters of the velocity of the center of pressure ranged from 0.361 to 0.912. These study results suggest that velocity of the center of pressure may be a useful measurement in future gait research.

Adult↗
PubMedDate not supplied

A unified method for calculating the center of pressure during wheelchair propulsion.

The measurement of the center of pressure (COP) has been and continues to be a successful tool for gait analysis. The definition of a similar COP for wheelchair propulsion. however, is not straightforward. Previously, a COP definition similar to that used in force plate analysis had been proposed. Unfortunately, this solution has the disadvantage of requiring a separate COP definition for each plane of analysis. A definition of the generalized center of pressure (GCOP) which is consistent in all planes of analysis is derived here. This definition is based on the placement of a force-moment system, equivalent to the force-moment system at the hub, on a line in space where the moment vector (wrench moment) is parallel to the force vector. The parallel force-moment system is then intersected with three planes defined by anatomical landmarks on the hand. Data were collected using eight subjects at propulsion speeds of 1.34 m/s and 2.24 m/s (1.34 m/s only for subject 1, 0.894 m/s and 1.79 m/s for subject 8). Each subject propelled a wheelchair instrumented with a SMARTwheel. A PEAK 5 video system was used to determine the position of anatomical markers attached to each subject's upper extremity. The GCOP in the transverse plane of the wrist formed clusters for all subject's except subject 2 at 1.34 m/s. The clustering of the GCOP indicates that the line of action for the force applied by the hand is approximately perpendicular to the transverse plane through the wrist. When comparing the magnitude of the moment vector part of the wrench with the moment of the force vector of the wrench about the hub, the wrench moment is approximately an order of magnitude smaller. This indicates that the role of the wrist for wheelchair propulsion is primarily to stabilize the force applied by the arm and shoulder.

Biomechanical Phenomena↗
PubMed1995

Errors in alignment of center of pressure and foot coordinates affect predicted lower extremity torques.

The purpose of the study was to quantify the effect of errors in spatial alignment between the center of pressure recorded from a force platform and the coordinates of the foot recorded from film on resultant joint torques in the lower extremity during the stance phase of gait. Two-dimensional kinematic and kinetic data from eight subjects performing walking and running were analyzed using inverse dynamics with the obtained center of pressure values and with +/- 0.5 and +/- 1.0 cm shifts in the anteroposterior location of the center of pressure under the support foot. Shifting the center of pressure posteriorly increased the flexor (dorsiflexor) torques at the hip and ankle and decreased the extensor (plantarflexor) torques at these joints. This shift also caused an increase in the extensor and a decrease in the flexor torques at the knee. Shifting the center of pressure anteriorly caused the opposite effects at each joint. The +/- 0.5 and +/- 1.0 cm shifts in the location of the center of pressure caused, on average, 7 and 14% changes, respectively, in maximum joint torque and angular impulse values. Relative transition times between flexor and extensor torques were either increased or decreased, on average, by 7 and 13%, respectively for the two conditions over all trials. Based on these results, it is concluded that due to potential errors in the spatial alignment of kinetic and kinematic data, joint torques in the literature on gait should be considered as approximations of the true values.

Adult↗
PubMed2006

Comparison of quantitative analysis and fractal analysis of center of pressure based on muscle fatigue.

To examine the influence of muscle fatigue on center of pressure displacement during quiet standing using quantitative and fractal analyses, 12 healthy young men and women did the exercise stress test on the triceps surae muscle until fatigued. Subjects were measured for body stability for 60 sec. before and after the exercise. Quantitative analysis showed that center-of-pressure parameters for distance, velocity, amplitude distribution, and mean vector length of sway in the anterior/posterior direction changed significantly after muscle fatigue but not on the periodic parameters. This result suggested that quantitative analysis may identify the effects of muscle fatigue on the parameters that show displacement in the anterior/posterior direction of center of pressure. Fractal analysis indicated the value of critical point coordinates increased after muscle fatigue. This analysis can clarify the fundamental postural control strategy and time-series characteristics of postural sway which cannot be identified by spectral analysis.

Adult↗