ABSTRACT Risk for cardiovascular disease (CVD) substantially increases during midlife (ages 40-60) and risk trajectories differ for women and men. Increasing physical activity (PA) can mitigate these risks and there is a critical need for research that can reduce barriers to engagement in this population. PA measurement reactivity, or a change in PA engagement in response to the introduction of PA measurement, may bias the objective assessment of PA that is essential to evaluating PA promotion efforts. At present, however, evidence supporting PA measurement reactivity as a key confound in PA research is mixed, including preliminary evidence from the investigative team. Our funded R03 is designed to address key limitations of existing work – including emphasis on children or healthy, young adults with low risk for CVD and lack of attention to individual differences between participants – among women in midlife with elevated CVD risk (e.g., obesity, hypertension; N = 800). The proposed supplement is designed to further address limitations of low power for conducting critical tests of gender differences in PA measurement reactivity responses, by including men and conducting the first fully powered test of gender differences in this area. We will use 6 existing datasets from NIH-funded clinical trials and publicly available databases to examine gender differences in PA measurement reactivity among midlife adults with elevated CVD risk (N = 1940). Using a coordinated analysis approach, we will employ multilevel modeling techniques to achieve the following aims: (1) To characterize midlife adults’ PA measurement reactivity across 4 PA outcomes (full sample and within genders): steps, minutes of light activity, minutes of moderate-to-vigorous intensity activity, and minutes of sedentary behavior, (2) To determine whether the presence or extent of measurement reactivity differ based on demographic, medical, or psychological characteristics (with emphasis on gender), and (3) To determine whether the presence or extent of measurement reactivity differ based on study characteristics such as research design (i.e., observation only vs. PA observation prior to the start of an intervention) and PA monitoring procedures (i.e., research-grade accelerometers vs. commercially available wearables). We will also examine whether gender moderates the influence of characteristics such as study design, BMI, or depressive symptoms. This work will identify circumstances associated with problematic levels of PA measurement reactivity among adults in midlife and potential gender-specific targets for reducing it in an at-risk group. This R03 supplement thus represents an important extension of funded work that leverages existing data sources to increase the scientific rigor of research in the fields of PA measurement and intervention, and to provide high-quality evidence that speaks to potential gender differences in PA measurement reactivity responses.

PROJECT NARRATIVE Adults in midlife (ages 40-60) are at unique risk for cardiovascular disease, in part due to decreases in physical activity, and there is a critical need for research that can reduce barriers to physical activity engagement. Reactivity to physical activity measurement (i.e., inflated physical activity engagement in response to the introduction of monitoring) poses a threat to these efforts, as it may bias activity estimates from monitoring devices, though it has not been examined in at-risk populations such as midlife adults and existing examinations of gender differences are inconsistent and underpowered. The proposed study will use a coordinated analysis approach to contribute to the scientific rigor of work in this area, by estimating the influence of and identifying study and participant characteristics associated with reactivity responses (particularly gender; N = 1940 across 6 studies), toward the goal of developing best practice recommendations for mitigating its effects in at-risk groups such as midlife adults.