Center Of Pressure Movement Research Articles

Exercise Therapy In Patients With Peripheral Neuropathy

Peripheral neuropathy is a pathology associated with damage to peripheral nerves, especially those of the extremities. Common symptoms of this condition include weakness, numbness, abnormal sensations and pain in feet, legs, arms, and/or hands. A recent literature search concluded there is inadequate evidence to evaluate the effects of exercise on functional ability in people with peripheral neuropathy. PURPOSE The primary objective was to assess the influence of exercise therapy on peripheral blood flow responses, heart rate variability and functional measures in a small sample of individuals with peripheral neuropathy. METHODS Participants engaged in an organized progressive exercise program 3*week for six weeks. The exercise program consisted of a typical walking program (with or without partial body weight support) or Tai Chi. Leg blood flow was evaluated, in both legs, at rest and following 5 minutes of arterial occlusion, using strain gauge plethysmography. Heart rate variability indices included standard deviation (SDNN), and low frequency (LF) and high frequency (HF) powers determined from EKG's obtained during 10 minutes of uninterrupted supine rest. Postural stability was defined as the average sway velocity in varied conditions on a force platform. Dynamic gait capability was defined as the center of pressure motion during walking on a treadmill. RESULTS To this point sixteen individuals (9 Women and 7 Men, Age: 68±7yrs, Height: 167±9cm, and Weight: 85±16kg) completed the exercise program. The program was well tolerated. No apparent differences in blood flow responses between the left and right legs were noted prior to the program. After 6 weeks, systolic blood pressure decreased (Pre: 135±15 Post: 126±14mmHg, p=0.001), whereas reactive hyperemic blood flow (RHBF) increased (Pre: 16.77±8.16 Post: 20.26±6.45ml/100ml/min, p=0.05). Moreover, changes in measures of heart rate variability suggest a favorable shift in autonomic modulation of the heart (Pre: LF/HF: 2.97±2.42 Post: 2.11±2.05, p=0.03). Finally, the changes in RHBF were associated with changes in SDNN (r2=0.39). Measures of postural stability improved significantly, whereas measures of dynamic gait capability only improved in those individuals involved in the walking program. CONCLUSION The results suggest that progressive exercise therapy is well tolerated in patients with peripheral neuropathy and may improve RHBF, HRV and postural stability. Improvements of measures of dynamic gait capability were specific to the modality of training used.

Aging effects on postural responses to self-imposed balance perturbations

The present study investigated how young and older individuals organize their posture in response to self-induced balance perturbations evoked by oscillatory single limb movements. Eleven old (70.1+/-4.3 years) and nine young (20.1+/-2.4 years) participants performed repeatedly for 5s hip flexion/extension movements using full range of motion and maximum velocity. Two-dimensional joint kinematics (sampling rate: 60Hz), center of pressure (CoP) and EMG activity of tibialis anterior (TA), medial gastrocnemius (MGAS) rectus femoris (RF) and, semitendinosus (ST) in the stance limb were recorded and analysed. Cross-correlation function (CCF) analysis was used to identify the degree of coupling between the swinging limb (SL), center of gravity (CoG) and CoP motions. Old adults significantly limited SL, CoG and CoP range of anterior/posterior (A/P) motion in response to the forceful leg swinging. In the stance limb, significantly lower levels of ankle muscle activity resulted in reduced hip and knee joint excursions and increased ankle instability. By contrast, young performers produced sufficient ankle muscle activity to stabilize the foot to the ground while progressively increasing joint range of motion from the ankle to the hip. Center of pressure and SL movements were strongly correlated in an anti-phase relationship in both age groups. In older adults, however, the relationship between CoG-SL and CoG-CoP movements was neither strong nor synchronous, reflecting a weaker coupling and lack of coordination between component movements. It is concluded that insufficient ankle muscle activity, central integration deficits and increased anxiety to postural threat are important factors implicated for the weaker postural synergies and freezing of degrees of freedom seen in the elderly during performance of single limb oscillations.

Simplest tasks have greatest dual task interference with balance in brain injured adults

Attention difficulties and poor balance are both common sequel following a brain injury. This study aimed to determine whether brain injured adults had greater difficulty than controls in performing a basic balance task while concurrently completing several different cognitive tasks varying in visuo-spatial attentional load and complexity. Twenty brain injured adults and 20 age-, sex- and education level-matched controls performed a balance-only task (step stance held for 30 s), five cognitive-only tasks (simple and complex non-spatial, visuo-spatial, and a control articulation task), and both together (dual tasks). Brain injured adults showed a greater centre of pressure (COP) excursion and velocity in all conditions than controls. Brain injured adults also demonstrated greater interference with balance when concurrently performing two cognitive tasks than control subjects. These were the control articulation and the simple non-spatial task. It is likely that distractibility during these simple tasks contributed to an increase in COP motion and interference with postural stability in stance. Performing visuo-spatial tasks concurrently with the balance task did not result in any change in COP motion. Dual task interference in this group is thus unlikely to be due to structural interference. Similarly, as the more complex tasks did not uniformly result in increased interference, a reduction in attentional capacity in the brain injured population is unlikely to be the primary cause of dual task interference in this group.

Quantitative evaluation of long sitting in paraplegic patients with spinal cord injury

Shirado O, Kawase M, Minami A, Strax TE. Quantitative evaluation of long sitting in paraplegic patients with spinal cord injury. Arch Phys Med Rehabil 2004;85:1251–6. Objectives To evaluate the characteristics of long sitting (ie, sitting with legs extended) in patients with spinal cord injury (SCI) and to compare these results with able-bodied control subjects. Design A kinematic study using a video camera and forceplate with a strain-gauge type load cell. Setting A referral center for patients with SCI in Japan. Participants Twenty-four subjects, including 11 able-bodied, matched control subjects and 13 SCI patients with complete paraplegia. Interventions Not applicable. Main outcome measures Sitting posture in the sagittal plane as well as the movement pattern and distance of the center of pressure (COP). Results Patients with SCI kept their pelvis tilted posteriorly and the lumbar spine was less lordotic during long sitting. The changing COP pattern during long sitting differed in able-bodied subjects as compared patients with SCI. During long sitting with arms outstretched over the thighs, COP movement in the subjects with SCI was significantly greater than that in the able-bodied subjects. When the arms were outstretched over the thighs, the COP shifted anteriorly in the able-bodied subjects and posteriorly in the patients with SCI. Conclusions Long sitting in the paraplegic patients with SCI was unstable compared with the able-bodied subjects. The COP distribution pattern differed significantly between the 2 groups. The support and function of the upper extremities may influence balance during long sitting in the patients with SCI. The method of seating evaluation using a video camera and gravicorder was easy to use and appeared to provide an objective measurement of dynamic seating function in the patients with SCI.

Is there interaction between vision and local fatigue of the lower limbs on postural control and postural stability in human posture?

An investigation of the interaction between local fatigue and vision on postural control and postural stability was carried out. Fatigue was effected in a sitting position and was assumed based on a shortening of the exertion time of the soleus muscles (60% of their maximal voluntary contractions). Postural stability was assessed by centre of gravity motion, which was computed from centre of pressure motion, evaluating postural control. Ten healthy male subjects were asked to stand as still as possible with eyes open (EO) and eyes closed (EC) before and after the fatigue protocol. Results showed that fatigue produced similar effects for the two vision conditions on postural control and postural stability analyzed separately, increasing postural control and leaving postural stability unchanged. Local fatigue essentially produced an increase of neuromuscular activity in high frequencies. However, this increase was more pronounced for the EO, as compared to the EC condition.

Postural and trunk muscle response to sudden release during stoop lifting tasks before and after fatigue of the trunk erector muscles

The effect of fatigue on the muscular and postural response to sudden release of different stoop lifting loads was studied. Ten male volunteers performed a series of stoop lifting trials before and after fatigue of the erector spinae. Trials were performed using loads of 20, 40, 60, and 80N, and sudden release of load was triggered randomly on one of the repetitions using an electromagnetic release. The onset of release was registered by an accelerometer, centre of pressure (COP) motion was recorded via a forceplate, and EMG activities of the latissimus dorsi (LD), erector spinae (ES), rectus abdominus (RA), external oblique (EO) and internal oblique (IO) muscles were recorded. A slightly reduced lifting speed was seen after fatigue, particularly at the higher loads, but this had little effect on the perturbing force at release, which was dominated by the release load. A significant effect of fatigue was seen on the antero-posterior COP motion, with the postural disturbance being decreased after fatigue. Fatigue resulted in a significant increase in ES (p = 0.029) and LD (p = 0.015) relaxation times and, while the response patterns (relaxation, contraction or no response) of the anterior trunk muscles (RA, EO, IO) were not always consistent, the proportion of response by relaxation was greater after fatigue. This resulted in a lower incidence but longer duration of co-contraction of the ES-RA, ES-EO and ES-EO muscle groups following fatigue, such that the mean co-contraction duration of these groups showed no significant differences before and after fatigue. The response to sudden release is a balance between maintaining postural stability and at the same time preventing the trunk musculature from overloading the spine and risking tissue injury. While fatigue of the trunk extensors does not appear to increase either the risk of fall or stumble or the incidence of co-contraction following sudden release of stoop lifting tasks, the duration of co-contraction appears to increase following fatigue. Further study is required to quantify the loading on the spine during sudden release of different lifting tasks before and after more realistic fatigue conditions.

Is there interaction between vision and local fatigue of the lower limbs on postural control and postural stability in human posture?

An investigation of the interaction between local fatigue and vision on postural control and postural stability was carried out. Fatigue was effected in a sitting position and was assumed based on a shortening of the exertion time of the soleus muscles (60% of their maximal voluntary contractions). Postural stability was assessed by centre of gravity motion, which was computed from centre of pressure motion, evaluating postural control. Ten healthy male subjects were asked to stand as still as possible with eyes open (EO) and eyes closed (EC) before and after the fatigue protocol. Results showed that fatigue produced similar effects for the two vision conditions on postural control and postural stability analyzed separately, increasing postural control and leaving postural stability unchanged. Local fatigue essentially produced an increase of neuromuscular activity in high frequencies. However, this increase was more pronounced for the EO, as compared to the EC condition.

Determinación de los patrones de comportamiento postural en población sana española

IntroductionPostural control in a standing position is externally reflected by the displacement of the centre of pressure (COP). It is necessary to determine COP movement normal patterns in order to obtain an accurate balance assessment Materials and methodologyA non pathological subject group was studied using NED/IBV s.v.e. evaluation equipment. Static trials based on Romberg’s test were undertaken in addition to the analysis trials of voluntary postural control ResultsNormal patterns have been obtained for the COP displacement and for the maximum forces produced in the anteroposterior and midlateral axes ConclusionsCOP movement comparative analysis, related to postural behaviour patterns of non-pathological persons, represents an accurate method to assess postural balance in a standing position. This information enables the design of individual and customised rehabilitation strategies in order to reduce the risk of falling

The effects of visual input on postural control of the lumbar spine in unstable sitting

Postural control of the lumbar spine in unstable sitting was quantified through the analysis of the center of pressure (CoP) movement recorded by a force plate situated underneath a seat that incorporated a hemisphere. Thirteen healthy subjects were tested under conditions of increasing seat instability and elimination of visual input. The purpose of this study was to determine the relative effects of visual input and support surface instability on open and closed loop postural control mechanisms in sitting and to determine the association between traditional summary statistics and random walk analysis of CoP movement. The effects of the seat instability level and visual input on the CoP movement parameters were tested with a two-factor, repeated measures ANOVA ( p<0.01). In all summary statistics CoP movement parameters increased significantly due to the seat instability level and lack of visual input. The random walk analysis identified two regions, short- and long-term, which has been postulated to represent open and closed loop control mechanism, respectively. While short-term scaling exponents were independent from visual input, CoP displacement in the short-term region was significantly increased in the eyes closed condition. Summary statistic of CoP total path length per second correlated highly with critical point coordinates and short-term diffusion coefficients. The CoP movement in the long-term region was consistent with a closed loop control mechanisms. The findings of visual influence on what is assumed as an open-loop control mechanism does not, at face value, support the hypothesis that two separate mechanisms are working to achieve postural control.

Voluntary control of postural equilibrium patterns

The ability to voluntarily transit from one whole-body movement to another is based on the multisensory integration of visual, vestibular, and somatosensory information. The role of functional sensory ranges and mechanical constraints on the ability to voluntarily transit between whole-body movements was studied by requiring subjects to switch from a head-fixed-to-surface to head-fixed-in-space postural pattern (and vice versa). The head-fixed-to-surface pattern required an erect stance characterized by an in-phase relationship between center of pressure (CoP) and platform motion. The head-fixed-in-space pattern required subjects to fix trunk–head position in-space while producing an anti-phase relationship between CoP and platform motion. The voluntary transition was performed with and without vision while standing on a surface oscillating in the anterior–posterior (A/P) direction. The support surface oscillated at five frequencies (0.2–1 Hz) with amplitude fixed at 15 cm. The voluntary transition was initiated with an auditory cue. The appropriate CoP-platform phase relationship for the two postural patterns was produced for all frequencies with and without vision. Upper-trunk kinematics revealed that subjects often failed to produce the head-fixed-to-surface pattern for frequencies ≥0.6 Hz, while producing the head-fixed-in-space pattern at all frequencies with vision. Without vision, neither pattern was produced consistently based on upper-trunk kinematics. These findings demonstrate separate control processes for upper- and lower-body motion and that functional sensory ranges and mechanical constraints can facilitate or inhibit voluntary production of whole-body movements based on these control processes. The results are discussed in reference to neurological substrates that may be involved in the planning and execution of motor set-switching. The experimental protocol we employ may also have application as a diagnostic tool for the evaluation of postural deficits.

An in vitro study of individual ankle muscle actions on the center of pressure.

The objective of this study was to correlate the effects of muscle force on the movement of the center of pressure (COP) for increased clinical utility of the COP measurement. Five fresh frozen cadaveric specimens were used to apply a 49 N sinusoidal muscle force to isolated or grouped extrinsic ankle muscles, and a constant ankle joint reaction force at different tibial positions. The muscle force and the vertical ground reaction force (GRF) play the role of a mechanical lever system so that the differential COP movement can be interpreted as a moment arm for the vertical GRF.

The role of task difficulty in the control of dynamic balance in children and adults

Although several studies have explored the development of balance control in children, few have addressed the influence of task difficulty on balance control under dynamic and ecologically valid conditions. In this study, reaching tasks in three directions to two distances enabled the examination of balance control in the context of graded task difficulty. Balance control was measured in younger (6 years) and older (10–11 years) children and adults using center of pressure (COP) measures (initial position, excursion, and amplitude) and reach distance. Measures of the initial position of the COP and the excursion of the COP revealed no age-related differences in balance control. Furthermore, balance control, measured by the amplitude of COP movement over the course of the reaching tasks, indicated no differences between the age groups for the least difficult and most difficult tasks. For tasks of moderate difficulty, however, older children displayed levels of balance control similar to younger children for some tasks and higher levels of balance control, similar to adults, for others. This study suggests that (1) process-based measures of balance control are more sensitive in detecting age-related differences, and (2) balance control depends upon both age and the difficulty of the task being performed.

Perception of Unsteadiness in Patients with Dizziness: Association with Handicap and Imbalance

Dizziness is a common problem in patients seeking medical help and is often associated with imbalance and handicap. This study aimed to reveal whether the perception of unsteadiness could be an indication of greater imbalance and handicap in these patients. Patients with dizziness were categorized into two groups, steady patients (n = 15) and unsteady patients (n = 23), based on the presence or absence of self-perceived unsteadiness. The level of self-perceived handicap was evaluated by the Dizziness Handicap Inventory. Static balance ability was evaluated using a force platform and the center of pressure motion was calculated during various quiet standing conditions. Dynamic balance ability was evaluated by the functional forward reach test and Dynamic Gait Index. All the patients also went through isometric strength tests of the lower extremities. It was found that all patients reported themselves to be handicapped by dizziness. Patients who perceived themselves to be unsteady had greater handicap and poorer static standing, but did not differ from the steady patients in regard to muscle strength or functional balance tests. Thus, self- perceived unsteadiness was associated with greater handicap and poorer static balance in dizzy patients. In clinical management of these patients, special attention should be paid to balance and handicap.

A comparison of rheumatoid arthritis and fibromyalgia patients and healthy controls exposed to a pulsed (200 μT) magnetic field: effects on normal standing balance

Specific weak time varying pulsed magnetic fields (MF) have been shown to alter animal and human behaviors, including pain perception and postural sway. Here we demonstrate an objective assessment of exposure to pulsed MF's on Rheumatoid Arthritis (RA) and Fibromyalgia (FM) patients and healthy controls using standing balance. 15 RA and 15 FM patients were recruited from a university hospital outpatient Rheumatology Clinic and 15 healthy controls from university students and personnel. Each subject stood on the center of a 3-D forceplate to record postural sway within three square orthogonal coil pairs (2 m, 1.75 m, 1.5 m) which generated a spatially uniform MF centered at head level. Four 2-min exposure conditions (eyes open/eyes closed, sham/MF) were applied in a random order. With eyes open and during sham exposure, FM patients and controls appeared to have similar standing balance, with RA patients worse. With eyes closed, postural sway worsened for all three groups, but more for RA and FM patients than controls. The Romberg Quotient (eyes closed/eyes open) was highest among FM patients. Mixed design analysis of variance on the center of pressure (COP) movements showed a significant interaction of eyes open/closed and sham/MF conditions [ F=8.78(1,42), P<0.006]. Romberg Quotients of COP movements improved significantly with MF exposure [ F=9.5(1,42), P<0.005] and COP path length showed an interaction approaching significance with clinical diagnosis [ F=3.2(1,28), P<0.09]. Therefore RA and FM patients, and healthy controls, have significantly different postural sway in response to a specific pulsed MF.

Effect of long-duration spaceflight on postural control during self-generated perturbations.

This report is the first systematic evaluation of the effects of prolonged weightlessness on the bipedal postural control processes during self-generated perturbations produced by voluntary upper limb movements. Spaceflight impacts humans in a variety of ways, one of which is compromised postflight postural control. We examined the neuromuscular activation characteristics and center of pressure (COP) motion associated with arm movement of eight subjects who experienced long-duration spaceflight (3--6 mo) aboard the Mir space station. Surface electromyography, arm acceleration, and COP motion were collected while astronauts performed rapid unilateral shoulder flexions before and after spaceflight. Subjects generally displayed compromised postural control after flight, as evidenced by modified COP peak-to-peak anterior-posterior and mediolateral excursion, and pathlength relative to preflight values. These changes were associated with disrupted neuromuscular activation characteristics, particularly after the completion of arm acceleration (i.e., when subjects were attempting to maintain upright posture in response to self-generated perturbations). These findings suggest that, although the subjects were able to assemble coordination modes that enabled them to generate rapid arm movements, the subtle control necessary to maintain bipedal equilibrium evident in their preflight performance is compromised after long-duration spaceflight.

How Does Calf-muscle Fatigue and Age Affect Vibration-perturbed One-leg Stance?

This study investigated the effect of muscle fatigue on vibration-perturbed one-leg stance in healthy young and older women. Force-plate measurements were obtained before and up to 15 min after fatiguing exercise of one leg. The study indicates an immediate but short-lasting effect of fatiguing exercise on vibration-induced centre of pressure (CP) oscillations in terms of increased amplitude. It also indicates that the influence of fatiguing exercise on the CP movements over time differs between young persons (20-26 years of age) and older persons (50-60 years of age). The normal learning effect due to repeated one-leg stance was not disturbed by the fatiguing exercise in the group of older persons in our study regarding sagittal CP velocity and frontal amplitude which was the case in the group of young persons. These results raise questions regarding postural control strategies and interpretation of force-plate data. Fatiguing exercise did not influence the shift of CP caused by vibration thus indicating...

Postural control of trunk during unstable sitting

A method for quantifying postural control of the lumbar spine during unstable sitting was developed. The unstable seat apparatus was equipped with leg and foot supports to isolate the control of the lumbar spine and trunk from the adjustments in the lower body joints. Polyester resin hemispheres with decreasing diameters were attached to the bottom of the seat to achieve increasing levels of task difficulty. The seat was placed on a force plate at the edge of a table and the participating subjects were instructed to maintain their balance while sitting on the seat. Coordinates of center of pressure (CoP) were recorded and quantified with summary statistics and random walk analysis. The CoP movement increased significantly with increased seat instability (task difficulty) ( p<0.01). Stabilogram plots of the CoP movement revealed short and long-term regions consistent with the hypothesis that the two regions reflect open and closed-loop postural control mechanisms. Repeatability of the CoP parameters was excellent for the summary statistics and the short-term random walk coefficients (0.77< R<0.96). It was fair for the long-term diffusion coefficients (0.56< R<0.57) and poor for the long-term scaling exponents (0.14< R<0.40). Summary statistics of the CoP movement were positively correlated with body weight (0.69< R<0.73) and the T9 to L4/L5 distance (0.43< R<0.54) of the subjects. This method can be applied to study the deficits in postural control of the lumbar spine in low-back pain population.

A prospective study of laboratory and clinical measures of postural stability to predict community-dwelling fallers.

The identification of specific risk factors for falls in community-dwelling elderly persons is required to detect early changes and permit a preventative approach to management. This study determines the ability of various laboratory measures and clinical tests of postural stability to prospectively predict fallers in community-dwelling elderly women. One hundred elderly women (65-86 years, mean age 73 +/- 5 years) performed a reaction-time step task, a limits of stability, and a quiet stance balance task. Postural muscle timing and movement speed were recorded during the step task. Center of pressure (COP) motion was recorded in quiet stance and at the limits of stability. Four common clinical balance tests were performed, and balance confidence, medical and activity history questionnaires were completed. Subjects were followed up regularly for a 6-month period following testing to determine the frequency and characteristics of any falls that occurred. Predictive capabilities of the balance measures to determine fallers were determined through logistic regression models. The clinical balance tests investigated were not able to predict fallers in this community-dwelling elderly population. A combination of variables from the laboratory tasks provided the best overall prediction rate (77%) of fallers (sensitivity 51%) and nonfallers (specificity 91%) from laboratory measures. Of these, step movement time and gluteus medius onset times were the factors best able to predict fallers. Alone, measures of COP motion in quiet stance and at the limits of stability had a poor ability to predict fallers, although they could correctly identify most nonfallers. Prediction was not significantly improved when clinical balance test results were added to the most predictive laboratory measures. Not all older adults with a reduction in balance ability reported a fall over a 6-month period. Of those who did, a combination of measures reflective of different aspects of mediolateral postural stability during a rapid step task, quiet stance, and movement to the limits of stability were best able to predict faller status, with nonfallers better predicted than fallers. These results emphasize the importance of the multifactorial nature of falls in the community-dwelling elderly population in that the clinical and laboratory measures did not predict a high proportion of fallers.

In-chair movement: validity, reliability and implications for measuring sitting discomfort

Sitting discomfort is traditionally evaluated with subjective rating scales which are referenced to an objective correlate (e.g. sitting posture) measured on a static (i.e. non-continuous) basis. Since sitting discomfort is dynamic in nature, it requires continuous, objective measurement. We therefore adapted an interface pressure mat to continuously record in-chair movement (ICM) as an indirect measurement of sitting discomfort by tracking the center of pressure (COP) at the buttock–chair interface. Here we report on two phases in the development of the COP system: laboratory validity and field reliability. In the laboratory study we confirmed system validity by simultaneously tracking ICM with the mat and a force platform ( r 2>0.80) and by comparing subjects’ COP movement with their gross trunk movements ( r 2>0.86). In our field study we used the intraclass correlation coefficient to establish a data sampling (i.e. selection) protocol that was reliable. We collected ICM data on seated telecommunications Directory Assistance operators during 2 h field tests. Results showed that using a minimum sampling time of 5 min and then averaging a series of 5 min samples of ICM was more reliable than single discrete samples. Using the averaging protocol, we also showed that ICM increased significantly over 2 h and that ICM did not differ between trials.

Analysis of the perception-action cycle for visually induced postural sway in 9-month-old sitting infants

Recent progress in understanding the adult’s postural control system comes from studying the relation between the timing of postural responses and visual motion. In this study, we sought to investigate this same relation in infants by testing the postural responses of 10 9-month-old infants sitting in a moving room. Trials were defined by the walls oscillating at different frequencies ranging from 0.2 to 0.8 Hz. In contrast to previous research with infants, we tested postural sway with multiple measures including center of pressure (COP), and head and lower back movements. The results revealed that all three measures were influenced by the driving frequency of the wall movements, but the pattern of this relation differed across measures. In particular, sway coherence between the head or lower back and room movements decreased with frequency, but sway coherence between the COP and room movements remained flat. The reasons for this pattern of results are discussed in terms of the type of control system necessary for producing postural sway to visual motion.