The relative contribution of psychological, social, and environmental variables to explain variation in leisure-time physical activity among adults at a population level

摘要

Background Information: There is substantial evidence demonstrating the significant benefits of regular physical activity (PA) and the burden of morbidity and mortality associated with inactivity. In Australia however, approximately 40% of the adult population is not meeting recommended levels of PA, the rates of inactivity may be increasing, and improving population levels of PA has been identified as a public health priority. Research is needed therefore, to develop a better understanding of the variables that limit and facilitate PA levels within the population, so as to guide the development of population-based PA promotion. Although a range of psychological, social and environmental variables have been associated with PA, few studies have integrated correlates across these domains and compared their relative contribution. The current evidence base is also limited by too few population-based studies, insufficient assessment of the measurement properties of correlate scales, minimal information on PA item non-response, and a lack of specificity among PA domains. Aims: This research program aimed to develop measures and examine the relative contributions of self-reported psychological, social, and environmental variables to explain variation in leisure-time PA (LTPA) among adults in the general population. Methods: This research program comprised three studies that utilised a crosssectional design and a mail survey methodology with a population-based random sample drawn from Brisbane, Australia (N=5000). Study one involved development and assessment of the measurement properties of a battery of scales to measure correlates of LTPA, using principal components and internal reliability analyses. Study two assessed the magnitude of and sociodemographic variables associated with LTPA item non-response on the mail survey, using logistic regression. Study three examined the independent contributions of self-reported psychological, social, and environmental variables to variation in walking, moderate- and vigorousintensity LTPA, using logistic regression adjusted for sociodemographic covariates. Results: Study one produced a battery of 28 scales to assess self-reported psychological, social and environmental correlates of LTPA. The scales used a total of 123 items to measure activity history (habit, mastery, exposure), health (physical, psychological), activity-related cognitions (self schemata, activity schemata, demand, need, knowledge), self-efficacy, anticipated benefits (psychological, health, challenge, improved appearance, social, weight management), perceived barriers (expense/low access, poor skill, poor personal functioning, time organization, disinterest, family obligations), social support (encouragement, discouragement) and neighborhood environment (available facilities, physical characteristics, aesthetic features, traffic). Of the 28 scales that were factorially derived, 25 had acceptable or marginal levels of internal consistency with Cronbach's alpha values ranging from 0.65 to 0.89. Study two indicated that 28% of the mail survey respondents had incomplete LTPA data with 8% of respondents missing the walking item, and 18% and 23% missing the vigorous-intensity and moderate-intensity LTPA items respectively. Respondents who missed all three LTPA items were more likely than those with complete LTPA data to be female, less educated, from low-income households, in poor health, and a current smoker. Respondents who missed the walking item were significantly more likely to be a current smoker, and to have limited education and low household income. Incomplete moderate-intensity LTPA data was associated with single parenthood and vocational education. Those who missed the vigorousintensity LTPA item were more likely to be 35-54 years old, in fair or poor health, and obese. Respondents with incomplete LTPA data were also more likely to miss sociodemographic items assessing education, household composition, and household income. In study three, the sociodemographic and correlate variables collectively accounted for 43% of the variation in total LTPA, 45% of vigorous-intensity LTPA, 26%of walking, and 22% of moderate-intensity LTPA (Nagelkerke R square). The individual correlates accounted for 0.0 - 4.0% of unique variation across the different domains of LTPA. Habit, self-efficacy, and social encouragement tended to contribute more unique variation for each LTPA domain. Physical health, discouragement, competition, and time management barriers contributed more unique variation to vigorous-intensity LTPA. Anticipated benefits of social interactions and weight management contributed more unique variation to moderate-intensity LTPA. Neighbourhood aesthetics contributed more unique variation to walking variation. Conclusions. This research program demonstrates the importance of integrating psychological, social, and environmental variables to explain PA, and that the relative importance of these correlates is likely to differ among PA domains. More research is needed to enhance the conceptualisation and measurement of correlate variables, in particular PA opportunities across the lifecourse, the anticipated benefit of a balanced lifestyle, the barriers of an unpredictable lifestyle and family obligations, social discouragement, and environmental variables. Population-based mail surveys of LTPA may under-represent population subgroups that are insufficiently active for health, and proactive strategies are needed to maximise their full participation in research and obtain complete survey data, in particular among individuals of low socioeconomic position and for the assessment of moderateintensity LTPA. Generic promotion to increase overall levels of LTPA in the population could focus on promoting self-efficacy for PA and habitual LTPA, as well as enhancing social encouragement. Tailored promotion for vigorous-intensity LTPA could reduce barriers associated with physical health, discouragement, competitiveness, and time management. Tailored promotion for moderate-intensity LTPA and walking should focus on supportive local neighbourhoods and promote the benefits of weight management and social interactions. In time, the successful implementation of such policy and promotion may arrest the decline of PA levels in the population, reduce preventable morbidity and mortality and economic burden associated with inactivity, and facilitate improved health for all Australians.