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

OBJECTIVE

To investigate the validity of MTI accelerometer as a physical activity (PA) measurement instrument for children with cerebral palsy (CP).

DESIGN

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.

SETTING

Data were collected on normal school days in special schools within the participants' 30-minute break period.

PARTICIPANTS

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).

INTERVENTIONS: Not applicable.

MAIN OUTCOME MEASURES: 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.

RESULTS

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.

CONCLUSIONS

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.