Validity and Reliability of Measures Obtained from the Balance Performance Monitor During Quiet Standing

The intra-rater reliability of the Balance Performance Monitor when measuring sitting symmetry and weight-shift activity after stroke in a community setting

Objective: To examine the intra-rater reliability of sitting symmetry and weight-shift activity measurements in poststroke adults.

Design: An intra-rater reliability study.

Setting: A community setting.

Subjects: Adult stroke survivors attending stroke support groups within the community of Nottingham (UK).

Main measures: The Balance Performance Monitor used to measure sitting symmetry and weight-shift activity. Intraclass correlation coefficients (ICCs) and their 95% confidence intervals (95% CI) were calculated. The Bland-Altman method for assessing agreement is also presented.

Results: We tested 49 participants (median age 73 years; interquartile range 68-81 years). Between-test reliability for sitting symmetry was high: ICC (1,1) = 0.93 (95% CI 0.87 ≤ ICC5 ≤ 0.96). The mean difference between the measures (d̄) was-0.08 (95% CI-0.48 ≤ d̄ ≤ 0.31); the standard deviation of the differences (SDdiff) was 1.383. The coefficient of repeatability was 2.76; the 95% limits of agreement were -2.850 and 2.682. Between-test reliability for weight-shift activity was also high: ICC (1,1) = 0.86 (95% CI 0.775 ≤; ICC5 ≤; 0.92). Bland-Altman d̄= - 0.08 (95%CI-0.19 ≤ d̄ ≤ 0.35), SDdiff = 0.936. The coefficient of repeatability was 1.87; the 95% limits of agreement were-1.792 and 1.952.

Conclusions: The 95% CI for d for both parameters crossed zero, indicating that between-test bias is unlikely. Sitting symmetry and weight-shift activity measures demonstrated acceptable levels of reliability.

Posture control development in children aged 2-7 years old, based on the changes of repeatability of the stability indices

One of the most common problems encountered in posture control studies is relatively poor repeatability of postural stability measures based on the COP (center of pressure) time-series which results from the inherent variability of postural control. The repeatability of the data reflecting the postural control mechanisms in young children is still not well enough explained. The differences between of the repeatability of the stability indices of left and right foot may reflect the lateralization development of legs in the support function. The aim of the present study was two-fold: the assessment of the repeatability of the stability indices in three consecutive trials in young children, aged 2-7 years old, during quiet bipedal stance and the description of process of lower limbs lateralization, based on the difference of repeatability of both feet stability the indices changing with years. The subjects were 272 young healthy children aged 2-7 years old separated in 6 groups for children of different age. Each child stood for around 90s on two AccuSway force platforms (AMTI). The shifts of COP beneath left and right legs were recorded onto a computer by using appropriate software compatible with platforms. The indices of the ellipse area and velocity COP shifts were calculated. For assessment of the repeatability the concordance correlation coefficient (CCC) of the indices was used between the 1st and 2nd, 2nd and 3rd, and 1st and 3rd trials. Young children of 2-4 years old exhibit low level of the stability indices repeatability which increases in 5-year-old children, 6-year-olds revealed both low and high and 7-year-olds good and high levels of repeatability. Youngest children showed higher repeatability of the ellipse area of the left leg, 3- and 4-year-olds the right leg, while 6-year-olds again the left leg. In 5- and 7-year-olds there were no differences in the repeatability of stability indices between the left and right foot. The comparisons of the repeatability of the velocity index between the left and right leg revealed the difference only in 3 years old children. Posture control development of children can be assessed on the basis of velocity index but the COP ellipse area index is better way to describe the lateralization process. The repeatability of the stability indices is poor from 2 to 4 year of life but increases significantly from 5 to 7 year of life. The comparisons of repeatability between the left and right foot indices reflect the developmental process of lateralization of lower limbs in the support function and reveal that the left lower leg is a dominant one in support function while standing position. The process of leg lateralization is finishing about 6th year of life.

Weight distribution in standing and sitting positions, and weight transfer during reaching tasks, in seated stroke subjects and healthy subjects

BACKGROUND AND PURPOSE

The recovery of sitting balance after a stroke is assumed to be essential to obtain independence in other vital functions. The purpose of the present study was to investigate weight distribution while sitting and standing still, and weight transfer during seated reaching tasks performed by stroke subjects and healthy subjects.

METHOD

The study was cross-sectional. Twenty-one stroke subjects and 21 healthy subjects, matched by age and gender, participated. Main measures were weight distribution while standing and sitting still, and displacements of centre ofpressure (COP) during seated reaching tasks. Data were collected using a balance performance monitor (BPM), including software.

RESULTS

Stroke subjects had less symmetrical weight distribution in standing than that of healthy subjects (p < 0.001). No significant differences between the groups were found while sitting still, and no associations between asymmetries in standing still and sitting positions within individual stroke subjects were found. Neither did the degree of weight distribution in sitting correspond to COP displacements in seated reaching tasks. However, COP displacement patterns in reaching tasks in the seated position were different in stroke subjects from those of healthy subjects. Stroke subjects showed more lateral displacement when reaching forwards (p < 0.001), and less lateral displacement when reaching sideways to the unaffected side (p = 0.01).

CONCLUSION

COP displacement patterns in stroke subjects deviate more than those of healthy subjects in seated reaching tasks. The deviating COP displacement patterns are discussed as a possible dysfunction in the ability to make postural adjustments and learn an efficient movement pattern.

The relationship between sitting stability and functional performance in patients with paraplegia11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated

OBJECTIVES

To compare sitting stability between patients with high and low thoracic spinal cord injury (SCI), to determine the factors that can predict sitting stability, and to examine the relationship between sitting stability and functional performance.

DESIGN

Cross-sectional assessment was performed on subjects with paraplegia.

SETTING

Rehabilitation hospital affiliated with a medical university.

PARTICIPANTS

Convenience sample of 30 adults with complete chronic thoracic SCI.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

(1) Postural sway during quiet sitting over 30 seconds was recorded as static sitting stability, and composite maximal weight-shift during leaning tasks over 30 seconds was measured as dynamic sitting stability; (2) age, body weight, trunk length, trunk strength, postonset duration, injury level, and presence of spasticity were examined as predictive variables for sitting stability; and (3) the time for completion of upper- and lower-body dressing and undressing and transfer was measured as functional performance.

RESULTS

A significant difference in composite maximal weight-shift was found between high and low thoracic SCI subjects (t=2.90, P<.01). Injury level and trunk length were 2 important predictive factors for dynamic sitting stability, and they explained 43.5% of the variance. Only the completion time of upper-body dressing and undressing correlated significantly with static (r=.465, P=.01) and dynamic (r=-.377, P<.05) sitting stability.

CONCLUSIONS

The subjects with low thoracic SCI showed better dynamic sitting stability than those with high thoracic SCI. Injury level and trunk length, not trunk flexion or extension strength, predicted the outcome of dynamic sitting stability. Measures were not precise enough to predict functional performance from the viewpoint of injury level and sitting stability. The underlying premise that a reduction or increase in trunk strength is indicative of poorer or better sitting stability in SCI individuals is questioned, and implications for problem identification and treatment planning are discussed.

Factors Affecting Reliability of the Biodex Balance System: A Summary of Four Studies

Purpose:

To describe differences in test-retest reliability of balance measures produced by the Biodex Balance System.

Methods:

Subjects performed balance tests in 4 studies, each involving two 30-second tests under varying conditions. Test-retest reliability coefficients were calculated for the overall stability index (SI) under each condition. Test-retest reliability was computed for subjects' limits of stability (LOS).

Results:

Intraclass correlation coefficients (ICC3,1) ranged from .44 to .89 for static balance tests; variability between the 2 tests ranged from 21% to 37%. Tests at lower stability levels or without visual input produced the highest ICCs. ICCs for the LOS tests ranged from .64 to .89. These measures were less variable (6% to 8%) than the static measures of balance.

Conclusions:

Test-retest reliability of the SI produced by the Biodex Balance System is acceptable for clinical testing and is comparable to other balance measures currently in use.

Validity of weight distribution and sway measurements of the Balance Performance Monitor

BACKGROUND AND PURPOSE

The Balance Performance Monitor (BPM) is a device which provides auditory and visual feedback on weight distribution and the magnitude of lateral and anterior-posterior sway during quiet standing. This study investigated the validity of the measurements provided by the BPM using a Kistler force plate (KFP) as the gold standard.

METHOD

Percentage weight distribution between the BPM foot plates was validated using both a series of calibration weights and the vertical component of ground reaction force, measured by the KFP, during normal standing in 18 young normal subjects. The lateral and anterior-posterior sway indices from the BPM were validated against the standard deviation of the position of the centre of pressure, again obtained using the KFP, during normal standing with eyes open and eyes closed and standing with feet together with eyes open. Concurrent validity of the percentage weight distribution measurements was assessed by calculating the 'limits of agreement' between the corresponding measurements from the BPM and KFP and the 95% confidence intervals for these 'limits'. Differences in the units of measurement obtained from the BPM and KFP resulted in the concurrent validity of the sway indices being assessed using correlation and regression.

RESULTS

Excellent agreement was found between the percentage weight distribution values provided by the BPM and the KFP, which showed that the BPM may read only 3% of body weight above or below that given by the KFP. High correlations (r = 0.61-0.99) were found between both the lateral and anterior-posterior sway indices from the BPM and the motion of the centre of pressure from the KFP in the respective direction. Despite this, further analysis of regression equations and the 95% prediction intervals showed poor concurrent validity of the BPM sway indices in relation to KFP measurements. This was thought to be due to the different methods by which the sway indices and the motion of the centre of pressure were calculated.

CONCLUSIONS

The BPM may be used to provide a valid measure of the symmetry aspect, but not necessarily the steadiness aspect of postural control.