Physical activity measurement using MTI (actigraph) among children with cerebral palsy.

Abstract

To investigate the validity of MTI accelerometer as a physical activity (PA) measurement instrument for children with cerebral palsy (CP). Participants were classified within Gross Motor Function Classification System I to III and took part in 2 activity sessions: (1) a structured activity protocol with increasing intensities and (2) a free play session. Concurrent measurements of activity counts, heart rate, and observed physical activity were performed. Data were collected on normal school days in special schools within the participants' 30-minute break period. Convenience sample of children with CP (N=31; 17 girls, 14 boys) age between 6 and 14 years (mean +/- SD, 9.71+/-2.52 y). Not applicable. MTI measured activity counts, a monitoring device measured heart rate, and the System for Observing Fitness Instruction Time (SOFIT) was used for direct PA observation. There were strong relationships between MTI and SOFIT (r=.75; R(2)=.56; P<.001) and heart rate monitor (HRM) and SOFIT (r=.65; R(2)=.43; P<.001) data in structured activities, but the difference between these 2 correlation coefficients was not significant (P=.46). In free play activities, the association between MTI and SOFIT data (r=.67; R(2)=.45; P<.001) was significantly stronger (P=.01) than that between heart rate and SOFIT data (r=.14; R(2)=.02; P<.001) . Bland-Altman plots showed better agreement between observed SOFIT and MTI-predicted SOFIT data than observed SOFIT and HRM-predicted SOFIT data from the linear regression analysis. The findings suggest that the MTI appears to be a valid instrument for measuring raw activity volume among children with CP and is suitable for use in studies attempting to characterize the PA of this population.