Author(s): HAN, K., Institution: CALIFORNIA STATE UNIVERSITY, NORTHRIDGE, Country: UNITED STATES, Abstract-ID: 396

INTRODUCTION:
Total travel distance (TTD) of the center of pressure (CoP) during single-leg stance has been shown to be a valid measure of postural balance [1]. TTD in cm was calculated by summing the displacement of the x and y components of the CoP as a function of time by applying the Pythagorean Theorem. The reliability of a single trial or averaged trials and the number of trials to average must be considered when using TTD. The purpose of the study was to determine a single trial and averaged trials reliability of TTD of the CoP in a single leg balance with eyes open, eyes closed, and eyes open on a foam surface.
METHODS:
A total of 12 (6 males, 6 females) healthy subjects (age = 23.8 ± 2.6 yrs, height = 157.5 ± 7.3 cm, mass = 51.3 ± 8.1 kg) participated in this study. Each subject completed 8 trials of single leg balance in each condition on a force platform with the order counterbalanced. The force data were sampled for 15 seconds at 60 Hz. TTD (cm) was measured in single leg stance and calculated according to the balance condition of each trial. Reliability was analyzed using SPSS to compute the intraclass correlation coefficient (ICC) with a 2-factor mixed-effects model and type consistency.
RESULTS:
For eyes open condition, there were significant differences in TTD between trials 1-8 (49.3 ± 13.7, 49.2 ± 12.7, 45.5 ± 11.1, 45.6 ± 11.0, 48.4 ± 17.1, 42.2 ± 9.9, 43.6 ± 11.8, 39.7 ± 9.0 cm), p = 0.026, respectively. Mean (SD) TTD in eyes open was 45.5 ± 10.0 cm with a single trial ICC of 0.609 and an averaged trials ICC of 0.926. In the eyes closed condition, there were significant differences in TTD between trials 1-8 (91.1 ± 35.8, 87.3 ± 27.7, 75.9 ± 21.5, 79.0 ± 16.4, 75.6 ± 15.6, 67.8 ± 21.0, 75.0 ± 20.7, 75.3 ± 22.9 cm), p = 0.027, respectively. Mean TTD in eyes closed was 78.4 ± 17.7 cm with a single trial ICC of 0.502 and an averaged trials ICC of 0.890. In the eyes open on foam condition, there were no differences in TTD between trials 1-8 (60.5 ± 20.6, 64.4 ± 16.7, 60.0 ± 23.1, 61.5 ± 18.9, 58.1 ± 16.3, 58.2 ± 18.8, 58.8 ± 15.0, 51.3 ± 13.8 cm), p = 0.161, respectively. Mean TTD in eyes open on foam was 58.9 ± 15.1 cm with a single trial ICC of 0.650 and an averaged trials ICC of 0.937.
CONCLUSION:
Averaging multiple trials of single leg balance improves the reliability of TTD (cm) measurement of the CoP. Further research is needed to identify possible interactions between trial-specific learning effect and fatigue when recording multiple trials in postural balance measurements.
REFERENCE:
1. Han et al (2009). Journal of Orthopaedic & Sports Physical Therapy, 39(4), 246-255, doi:10.2519/jospt.2009.2958