Measuring physical activity in young people with cerebral palsy: validity and reliability of the ActivPAL™ monitor.

BACKGROUND AND PURPOSE: We determined the criterion validity and the retest reliability of the ΑctivPAL™ monitor in young people with diplegic cerebral palsy (CP). METHODS: Activity monitor data were compared with the criterion of video recording for 10 participants. For the retest reliability, activity monitor data were collected from 24 participants on two occasions. Participants had to have diplegic CP and be between 14 and 22 years of age. They also had to be of Gross Motor Function Classification System level II or III. Outcomes were time spent in standing, number of steps (physical activity) and time spent in sitting (sedentary behaviour). RESULTS: For criterion validity, coefficients of determination were all high (r(2) ≥ 0.96), and limits of group agreement were relatively narrow, but limits of agreement for individuals were narrow only for number of steps (≥5.5%). Relative reliability was high for number of steps (intraclass correlation coefficient = 0.87) and moderate for time spent in sitting and lying, and time spent in standing (intraclass correlation coefficients = 0.60-0.66). For groups, changes of up to 7% could be due to measurement error with 95% confidence, but for individuals, changes as high as 68% could be due to measurement error. DISCUSSION: The results support the criterion validity and the retest reliability of the ActivPAL™ to measure physical activity and sedentary behaviour in groups of young people with diplegic CP but not in individuals.