Background/Purpose: A common protocol for measuring physical activity in children involves measurement across four days, three weekdays and one weekend day. The purpose of this study was to evaluate whether this four-day protocol is appropriate for children and adolescents with Down syndrome (DS) employing a Generalizability study (G-study). We also wanted to establish the minimum number of days needed through a Decision study (D-study).
Method: The pre-intervention data were collected from 43 children and adolescents with DS in the age range between 8 and 15 years (Mean age=11.7±2.2). The participants were asked to wear an Actical accelerometer for seven consecutive days during the first week of April and the first week of June. They were excluded if they failed to wear the accelerometer for a minimum of ten hours per day, and at least four of the seven days including one weekend day which has been previously established.
Analysis/Results: Based on the results of the G-study, it appears that four days of measurement which includes one weekend day is appropriate for participants with DS (r=.87). The results of the D-study demonstrate that measuring physical activity for one or two days results in generalizability coefficients below .80, while measuring physical activity for three or more days achieves generalizability coefficients of .80 or higher.
Conclusions: Based on these results, it appears that a minimum of three days is necessary to establish a stable measurement of physical activity using the Actical accelerometer with children and adolescents with DS.
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