Željko Pedišić

Accelerometer-based measures in physical activity surveillance: current practices and issues

Objective Self-reports of physical activity (PA) have been the mainstay of measurement in most non-communicable disease (NCD) surveillance systems. To these, other measures are added to summate to a comprehensive PA surveillance system. Recently, some national NCD surveillance systems have started using accelerometers as a measure of PA. The purpose of this paper was specifically to appraise the suitability and role of accelerometers for population-level PA surveillance. Methods A thorough literature search was conducted to examine aspects of the generalisability, reliability, validity, comprehensiveness and between-study comparability of accelerometer estimates, and to gauge the simplicity, cost-effectiveness, adaptability and sustainability of their use in NCD surveillance. Conclusions Accelerometer data collected in PA surveillance systems may not provide estimates that are generalisable to the target population. Accelerometer-based estimates have adequate reliability for PA surveillance, but there are still several issues associated with their validity. Accelerometer-based prevalence estimates are largely dependent on the investigators’ choice of intensity cut-off points. Maintaining standardised accelerometer data collections in long-term PA surveillance systems is difficult, which may cause discontinuity in time-trend data. The use of accelerometers does not necessarily produce useful between-study and international comparisons due to lack of standardisation of data collection and processing methods. To conclude, it appears that accelerometers still have limitations regarding generalisability, validity, comprehensiveness, simplicity, affordability, adaptability, between-study comparability and sustainability. Therefore, given the current evidence, it seems that the widespread adoption of accelerometers specifically for large-scale PA surveillance systems may be premature.

Physical activity in different domains and health-related quality of life: a population-based study

PurposeThe purpose of this study was to determine the association between physical activity (PA) in different domains (job-related, domestic, transportation, and leisure-time) and health-related quality of life (HRQoL).MethodsWe used the long version of IPAQ and SF-36 to assess PA and HRQoL, respectively, in a random sample of 1,076 Croatian inhabitants.ResultsMultiple regression analyses showed a significant relationship between PA and Vitality, Mental Health, and mental summary component score in female participants and Physical Functioning, Bodily Pain, Social Functioning, Mental Health, and physical summary component score in male participants (multiple R range, 0.14–0.21). Leisure-time PA was positively related to HRQoL (β range, 0.11–0.18), whereas transportation (β range, −0.10 to −0.14) and domestic (β range, −0.10 to −0.12) PA was inversely related to HRQoL when adjusted for size of settlement, age, educational level, cigarette consumption, alcohol consumption, and body mass index.ConclusionsOur study added useful information to the body of evidence on the positive correlation between leisure-time PA and HRQoL. Since transportation and domestic PA were inversely related with several HRQoL scales, in future studies on the relationship between PA and HRQoL it is important to assess domain-specific PA and not only total PA.

Reliability of a Photographic Method for Assessing Standing Posture of Elementary School Students

OBJECTIVE A high prevalence of poor standing posture among elementary schoolchildren indicates the need for the introduction of school-based interventions for improvement of postural alignments. For assessing the effect of intervention programs, reliable quantitative measures of standing posture should be used. Therefore, the purpose of this study was to examine the reliability of a photographic method for assessment of standing posture among elementary schoolchildren. METHODS The study was conducted on a convenience sample of 273 male students between 10 and 13 years old. Each subject was photographed in habitual standing posture, 3 times in a front view and 3 times in a side view. Deviations from ideal postural alignment were calculated with Posture Image Analyzer software and UTHSCSA ImageTool software. Interitem reliability was estimated using intraclass correlation coefficient. RESULTS Intraclass correlation coefficients for posture deviations assessed with Posture Image Analyzer ranged from 0.81 for knee joints deviation and ankle joints deviation in the coronal plane to 0.92 for trunk deviation and knee joints deviation in the sagittal plane. Intraclass correlation coefficients for posture deviations assessed with UTHSCSA ImageTool ranged from 0.80 for knee joints deviation in the coronal plane to 0.91 for trunk deviation and knee joints deviation in the sagittal plane. CONCLUSIONS This study showed a satisfactory interitem reliability of a photographic method for the assessment of standing posture among elementary schoolchildren.

Compositional data analysis for physical activity, sedentary time and sleep research

The health effects of daily activity behaviours (physical activity, sedentary time and sleep) are widely studied. While previous research has largely examined activity behaviours in isolation, recent studies have adjusted for multiple behaviours. However, the inclusion of all activity behaviours in traditional multivariate analyses has not been possible due to the perfect multicollinearity of 24-h time budget data. The ensuing lack of adjustment for known effects on the outcome undermines the validity of study findings. We describe a statistical approach that enables the inclusion of all daily activity behaviours, based on the principles of compositional data analysis. Using data from the International Study of Childhood Obesity, Lifestyle and the Environment, we demonstrate the application of compositional multiple linear regression to estimate adiposity from children’s daily activity behaviours expressed as isometric log-ratio coordinates. We present a novel method for predicting change in a continuous outcome based on relative changes within a composition, and for calculating associated confidence intervals to allow for statistical inference. The compositional data analysis presented overcomes the lack of adjustment that has plagued traditional statistical methods in the field, and provides robust and reliable insights into the health effects of daily activity behaviours.

Domain-specific physical activity and health-related quality of life in university students

Abstract Information on the relationship between domain-specific physical activity (PA) and health-related quality of life (HRQoL) in the general population and specific groups is still scarce. The aim of this study was to determine the relationship between PA in work, transport, domestic and leisure-time domains and HRQoL among university students. PA and HRQoL were assessed in a random stratified sample of 1750 university students using the International Physical Activity Questionnaire – long form and 12-item Short Form Health Survey, respectively. The Spearmans rank correlations, adjusted for age, community size, personal monthly budget, body mass index, smoking habits and alcohol intake ranged from −0.11 to 0.18 in female students and −0.29 to 0.19 in male students. Leisure-time, domestic, transport-related PA and total PA were positively related to HRQoL. Inverse correlations with HRQoL were only found for work-related PA in male students. Multiple linear regression analysis showed that only leisure-time PA was related to the Physical Summary Component score (β = 0.08 for females and β = 0.10 for males, P < 0.05). Domain-specific PA levels were not significantly related to the Mental Component Summary score. To get a more comprehensive insight in the relationship between PA and HRQoL, future studies should not only analyse total PA levels but also domain-specific PA levels. The evidence on the positive relationship of leisure-time, transport and domestic PA with HRQoL can potentially be used to support evidence-based promotion of PA in a university setting, and as a hypothesis for future longitudinal studies on such potential causal relationships.

The compositional isotemporal substitution model: A method for estimating changes in a health outcome for reallocation of time between sleep, physical activity and sedentary behaviour:

How people use their time has been linked with their health. For example, spending more time being physically active is known to be beneficial for health, whereas long durations of sitting have been associated with unfavourable health outcomes. Accordingly, public health messages have advocated swapping strategies to promote the reallocation of time between parts of the time-use composition, such as “Move More, Sit Less”, with the aim of achieving optimal distribution of time for health. However, the majority of research underpinning these public health messages has not considered daily time use as a composition, and has ignored the relative nature of time-use data. We present a way of applying compositional data analysis to estimate change in a health outcome when fixed durations of time are reallocated from one part of a particular time-use composition to another, while the remaining parts are kept constant, based on a multiple linear regression model on isometric log ratio coordinates. In an example, we examine the expected differences in Body Mass Index z-scores for reallocations of time between sleep, physical activity and sedentary behaviour.

Are total, intensity- and domain-specific physical activity levels associated with life satisfaction among university students?

Background Thorough information about the relationship between physical activity (PA) and life satisfaction is still lacking. Therefore, this study examined the cross-sectional relationships between life satisfaction and meeting the World Health Organization (WHO) moderate to vigorous-intensity PA recommendations, total volume and duration of PA, intensity-specific PA (walking, moderate- and vigorous-intensity), domain-specific PA (work, transport-related, domestic, and leisure-time), and 11 domain and intensity-specific PA types among university students. Additionally, we examined the associations between life satisfaction and gender, age, disposable income, community size, smoking, alcohol intake, body mass index (BMI), and self-rated health. Methods The study included a random sample of 1750 university students in Zagreb, Croatia (response rate = 71.7%; 62.4% females; mean age 21.5 ± 1.8 years), using the International Physical Activity Questionnaire — long form and the Satisfaction with Life Scale. Results Higher life satisfaction was associated with female gender (β = 0.13; p = <0.001), younger age (β = -0.07; p = 0.024), higher disposable income (β = 0.10; p = 0.001), and better self-rated health (β = 0.30; p = <0.001). No significant association was found between life satisfaction and size of community (p = 0.567), smoking status (p = 0.056), alcohol consumption (p = 0.058), or BMI (p = 0.508). Among all PA variables, only leisure-time vigorous-intensity PA was significantly associated with life satisfaction after adjustments for socio-demographic characteristics, lifestyle and self-rated general health (β = 0.06; p = 0.045). Conclusions This study indicated a weak positive relationship between leisure-time vigorous-intensity PA and life satisfaction, whilst no such association was found for other PA variables. These findings underscore the importance of analyzing domain and intensity-specific PA levels in future studies among university students, as drawing conclusions about the relationship between PA and life satisfaction based on total PA levels only may be misleading.

Objective Measurement in Physical Activity Surveillance: Present Role and Future Potential

Measuring physical activity at the population level is the central component of a physical activity surveillance system. These systems are used to monitor trends at the national level, identify sub-groups at risk of low activity, and to assess the long-term impact of policies and public health programs targeting physical activity. Surveillance measures assess physical activity in large samples to provide estimates generalizable to whole populations, and must be used in identical ways over many years. They need to be convenient, affordable and feasible to implement in population-representative samples, with good participants’ adherence to the measurement tasks required. Thus, surveillance measures pose special challenges for objective assessment of physical activity. Objective assessment of physical activity in populations started in the 1980s, with efforts to measure cardiorespiratory fitness and energy expenditure. These measures were costly, placed a substantial burden on participants, and selection effects limited their generalizability. Since around 2000, population objective assessment has been carried out in several countries using motion-sensing accelerometers. These can measure the intensity and duration of most ambulatory activities, walking and running. They produce population prevalence estimates of meeting physical activity guidelines of around 5 % for adults, rates that are much lower than those assessed by self-reports. In addition, simpler pedometers that record step-counts are also used in population studies. When compared to accelerometers, which are influenced by regular changes in device models and cut points, pedometers generally provide more comparable estimates over time. However, their comprehensiveness is limited, as they only assess step counts. Most recently, ‘wearable technology’ has burgeoned, with accelerating growth in the sales of devices such as Fitbits and Jawbone since around 2012. These devices, alongside smart phones and smart watches (that also have accelerometers and other motion sensors built in), provide the potential to reach millions of people. However, the reliability and validity of these devices is not well understood. Further, the models are updated very frequently, which does not influence their usefulness for individuals, but does compromise their potential in population surveillance. The challenge will be to identify affordable technology that is exactly comparable over many years to monitor population physical activity levels.

Validation of the folate food frequency questionnaire in vegetarians

Adequate folate status has an important role in the prevention of chronic and developmental diseases and is considered a potential public health issue. Therefore, valid tools for measuring the vitamin intake are needed. In our previous study a folate food frequency questionnaire (FFQ) designed to measure dietary folate equivalents was developed and validated among adult women against serum and erythrocyte (red blood cell) folate and plasma homocysteine. The aim of the present study was to validate the FFQ in vegetarians (n=75). The Pearson correlation for folate intake and biomarkers was 0.41, 0.36 and −0.15 for serum and red blood cell folate and plasma homocysteine, respectively. The quadratic weighted kappa value for biomarkers was above 0.2 and the gross misclassification of subjects into quartiles was less than 10%. The FFQ is a valid tool for measuring dietary folate equivalent intake in Croatian vegetarians.