Reliably Measuring Ambulatory Activity Levels of Children and Adolescents With Cerebral Palsy

Objective: To identify sources of variance in step counts and to examine the minimum number of days required to obtain a stable measure of habitual ambulatory activity in the cerebral palsy (CP) population. Design: Cross-sectional. Setting: Free-living environments: Participants: Children and adolescents with CP (N=209; mean age +/- SD, 8y, 4mo +/- 3y, 4mo; n=118 boys; Gross Motor Function Classification System [GMFCS] levels I-III) were recruited through 3 regional pediatric specialty care hospitals. Interventions: Daily walking activity was measured with a 2-dimensional accelerometer over 7 consecutive days. An individual information-centered approach was applied to days with <100 steps, and participants with >= 3 days of missing values were excluded from the study. Participants were categorized into 6 groups according to age and functional level. Generalizability theory was used to analyze the data. Main Outcome Measures: Mean step counts, relative magnitude of variance components in total step activity, and generalizability coefficients (G coefficients) of various combinations of days of the week. Results: Variance in step counts attributable to participants ranged from 33.6% to 65.4%. For youth ages 2 to 5 years, a minimum of 8, 6, and 2 days were required to reach acceptable G coefficient (reliability) of >=.80 for GMFCS levels I, II, and III, respectively. For those ages 6 to 14 years, a minimum of 6, 5, and 4 days were required to reach stable measures of step activity for GMFCS levels I, II, and III, respectively. Conclusions: The findings of the study suggest that an activity-monitoring period should be determined based on the GMFCS levels to reliably measure ambulatory activity levels in youth with CP. Archives of Physical Medicine and Rehabilitation 2013;94:132-7 (C) 2013 by the American Congress of Rehabilitation Medicine