Original article
Physical Activity Measurement Using MTI (Actigraph) Among Children With Cerebral Palsy

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Abstract

Capio CM, Sit CH, Abernethy B. 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±2.52y).

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; R2=.56; P<.001) and heart rate monitor (HRM) and SOFIT (r=.65; R2=.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; R2=.45; P<.001) was significantly stronger (P=.01) than that between heart rate and SOFIT data (r=.14; R2=.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.

Section snippets

Participants

A convenience sample of 31 children with CP (17 girls, 14 boys) between ages of 6 and 14 years (mean ± SD, 9.71±2.52y) participated in the study. The sample size was based on a balance between the difficulty in procuring large samples of children with CP and previous suggestions that studies need at least 15 participants for each predictor variable in order to develop reliable regression equations.32 The participants were recruited from 2 special schools for children with physical disabilities.

Structured Activity

The structured activity session was designed to represent a stepwise increase in intensity of physical activities. Table 2 shows the means and SDs for the MTI, HRM, and SOFIT outputs for the 6 protocol activities, with predictably greater activity outputs found in the higher levels of the structured activity protocol.

Results of the Pearson correlations and linear regression analyses indicated that all 3 activity measures increased across the higher levels of the structured activity protocol in

Discussion

The protocol in the structured activity sessions engaged the participants in a series of activities that were designed to have a stepwise increase in intensity. Observed PA levels as measured by SOFIT demonstrated a very strong, significant, and positive linear association with the activity protocol, confirming the evidence that direct observation is an appropriate criterion measure for PA measurement validity studies,19, 21, 23, 24 particularly among children.37 In an earlier calibration study

Conclusions

The present study concludes that the MTI appears to be a valid measure of activity volume among children with CP in both structured and free play activities. The findings support the potential use of MTI in field-based studies that aim to monitor the habitual PA of children with CP, including studies examining the effects of interventions. A minimum of 7 days of monitoring is required to assess children's habitual PA reliably,38 including weekdays and weekends.39 Similar considerations may have

Acknowledgments

We thank Tina Chan, PT and Kathlynne Eguia, PT for facilitating the data collection. Special thanks to the participating children with CP and to their parents as well.

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