Measuring Physical Activity in a Cardiac Rehabilitation Population Using a Smartphone-Based Questionnaire

Background: Questionnaires are commonly used to assess physical activity in large population- based studies because of their low cost and convenience. Many self- report physical activity questionnaires have been shown to be valid and reliable measures, but they are subject to measurement errors and misreporting, often due to lengthy recall periods. Mobile phones offer a novel approach to measure self- reported physical activity on a daily basis and offer real- time data collection with the potential to enhance recall. Objective: The aims of this study were to determine the convergent validity of a mobile phone physical activity (MobilePAL) questionnaire against accelerometry in people with cardiovascular disease (CVD), and to compare how the MobilePAL questionnaire performed compared with the commonly used self- recall International Physical Activity Questionnaire (IPAQ). Methods: Thirty adults aged 49 to 85 years with CVD were recruited from a local exercise- based cardiac rehabilitation clinic in Auckland, New Zealand. All participants completed a demographics questionnaire and underwent a 6- minute walk test at the first visit. Subsequently, participants were temporarily provided a smartphone (with the MobilePAL questionnaire preloaded that asked 2 questions daily) and an accelerometer, which was to be worn for 7 days. After 1 week, a follow- up visit was completed during which the smartphone and accelerometer were returned, and participants completed the IPAQ. Results: Average daily physical activity level measured using the MobilePAL questionnaire showed moderate correlation (r=.45; P=.01) with daily activity counts per minute (Acc_CPM) and estimated metabolic equivalents (MET) (r=.45; P=.01) measured using the accelerometer. Both MobilePAL (beta=.42; P=.008) and age (beta=-.48, P=.002) were significantly associated with Acc_CPM (adjusted R-2=.40). When IPAQ- derived energy expenditure, measured in MET- minutes per week (IPAQ_ met), was considered in the predicted model, both IPAQ_met (beta=.51; P=.001) and age (beta=-.36; P=.016) made unique contributions (adjusted R-2=. 47, F-2,F-27= 13.58; P<.001). There was also a significant association between the MobilePAL and IPAQ measures (r=.49, beta=.51; P=.007). Conclusions: A mobile phone- delivered questionnaire is a relatively reliable and valid measure of physical activity in a CVD cohort. Reliability and validity measures in the present study are comparable to existing self- report measures. Given their ubiquitous use, mobile phones may be an effective method for physical activity surveillance data collection.