Balance in single-limb stance in healthy subjects--reliability of testing procedure and the effect of short-duration sub-maximal cycling

Abstract

Background: To assess balance in single-limb stance, center of pressure movements can be registered by stabilometry with force platforms. This can be used for evaluation of injuries to the lower extremities. It is important to ensure that the assessment tools we use in the clinical setting and in research have minimal measurement error. Previous studies have shown that the ability to maintain standing balance is decreased by fatiguing exercise. There is, however, a need for further studies regarding possible effects of general exercise on balance in single-limb stance. The aims of this study were: 1) to assess the test-retest reliability of balance variables measured in single-limb stance on a force platform, and 2) to study the effect of exercise on balance in single-limb stance, in healthy subjects.

Methods: Forty-two individuals were examined for test-retest reliability, and 24 individuals were tested before (pre-exercise) and after (post-exercise) short-duration, sub-maximal cycling. Amplitude and average speed of center of pressure movements were registered in the frontal and sagittal planes. Mean difference between test and retest with 95% confidence interval, the intraclass correlation coefficient, and the Bland and Altman graphs with limits of agreement, were used as statistical methods for assessing test-retest reliability. The paired t-test was used for comparisons between pre- and post-exercise measurements.

Results: No difference was found between test and retest. The intraclass correlation coefficients ranged from 0.79 to 0.95 in all stabilometric variables except one. The limits of agreement revealed that small changes in an individual's performance cannot be detected. Higher values were found after cycling in three of the eight stabilometric variables.

Conclusions: The absence of systematic variation and the high ICC values, indicate that the test is reliable for distinguishing among groups of subjects. However, relatively large differences in an individual's balance performance would be required to confidently state that a change is real. The higher values found after cycling, indicate compensatory mechanisms intended to maintain balance, or a decreased ability to maintain balance. It is recommended that average speed and DEV 10; the variables showing the best reliability and effects of exercise, be used in future studies.

Figure 1

Stabilometry in single-limb stance, tested by means of a strain gauge force plate. A standardized position was used. The subject is a model who did not participate in the study.

Figure 2

Bland and Altman graph with limits of agreement (LOA). The differences between test sessions 1 and 2 (test 2 minus test 1) plotted against their mean for each subject for the amplitude in mm in the frontal plane (FP) in 42 healthy subjects, together with the 95% confidence interval (CI) and the 95% LOA.

Figure 3

Bland and Altman graph with limits of agreement (LOA). The differences between test sessions 1 and 2 (test 2 minus test 1) plotted against their mean for each subject for the amplitude in mm in the sagittal plane (SP) in 42 healthy subjects, together with the 95% confidence interval (CI) and the 95% LOA.

Figure 4

Bland and Altman graph with limits of agreement (LOA). The differences between test sessions 1 and 2 (test 2 minus test 1) plotted against their mean for each subject for the average speed in mm·s^-1 in the frontal plane (FP) in 42 healthy subjects, together with the 95% confidence interval (CI) and the 95% LOA.

Figure 5

Bland and Altman graph with limits of agreement (LOA). The differences between test sessions 1 and 2 (test 2 minus test 1) plotted against their mean for each subject for the average speed in mm·s^-1 in the sagittal plane (SP) in 42 healthy subjects, together with the 95% confidence interval (CI) and the 95% LOA.

Figure 6

Bland and Altman graph with limits of agreement (LOA). The differences between test sessions 1 and 2 (test 2 minus test 1) plotted against their mean for each subject for the number of movements exceeding 5 mm (DEV 5) in the frontal plane (FP) in 42 healthy subjects, together with the 95% confidence interval (CI) and the 95% LOA.

Figure 7

Bland and Altman graph with limits of agreement (LOA). The differences between test sessions 1 and 2 (test 2 minus test 1) plotted against their mean for each subject for the number of movements exceeding 5 mm (DEV 5) in the sagittal plane (SP) in 42 healthy subjects, together with the 95% confidence interval (CI) and the 95% LOA.

Figure 8

Bland and Altman graph with limits of agreement (LOA). The differences between test sessions 1 and 2 (test 2 minus test 1) plotted against their mean for each subject for the number of movements exceeding 10 mm (DEV 10) in the frontal plane (FP) in 42 healthy subjects, together with the 95% confidence interval (CI) and the 95% LOA.

Figure 9

Bland and Altman graph with limits of agreement (LOA). The differences between test sessions 1 and 2 (test 2 minus test 1) plotted against their mean for each subject for the number of movements exceeding 10 mm (DEV 10) in the sagittal plane (SP) in 42 healthy subjects, together with the 95% confidence interval (CI) and the 95% LOA.