Reliability of Center of Pressure Measures for Assessing the Development of Sitting Postural Control

64 Objectives: To determine the reliability of linear and nonlinear tools, including intraand inter65 session reliability, when used to analyze the center of pressure (COP) time series during the 66 development of infant sitting postural control. 67 Design: Longitudinal study 68 Setting: University hospital laboratory 69 Participants: Thirty three typically developing infants (mean age at entry in the study ± standard 70 deviation, 152.4 ± 17.6 days). 71 Interventions: Not applicable 72 Main Outcome Measures: Infants were tested twice in one week at each of the four months of the 73 study. Sitting COP data was recorded for three trials at each session (two each month within one 74 week). The linear COP parameters of root mean square (RMS) and range of sway for both the 75 anterior-posterior (AP) and the medial-lateral (ML) directions, and the sway path, were calculated. 76 In addition, the nonlinear parameters of approximate entropy (ApEn), Lyapunov exponent (LyE), 77 and correlation dimension (CoD) for both directions were also calculated. Intra-session and inter78 session reliability was quantified by the intraclass correlation coefficient (ICC). 79 Results Conclusions: Our results showed that the evaluation of COP data is a reliable method of 80 investigating the development of sitting postural control. In particular, the nonlinear tool of ApEn 81 presented high intraand intersession ICC values in comparison to all other parameters evaluated. 82 Generally, intraand intersession reliability increased in the last two months of the data 83 collections and as sitting posture matured. The present study emphasizes the need for establishing 84 COP reliability before using it as a method of examining intervention progress directed at 85 improving the sitting postural abilities in infants with motor developmental delays. 86