The current USDHHS guidelines recommend that adults expend at least 1000 kcal per week in PA,12 which can be obtained through 150 minutes per week of moderate intensity PA, 75 minutes of vigorous intensity PA, or some combination. However, current estimates suggest that only 3.5% to 43.5% of US adults, and 28% of overweight or obese adults adhere to these recommendations.13-16 Moreover, people across all World Health Organization regions become less active as they age.17 A more progressive decline in PA is seen after age 45- 50.15,18 In essence, PA rates tend to decrease as people age and gain weight while the health benefits of PA become more pronounced. A growing body of research19-36 suggests that a shift in national guidelines to emphasize PA of a self-selected intensity (i.e., self-paced) instead of prescribed moderate intensity PA may result in better adherence to PA programs, particularly among overweight and obese midlife adults.37,38 In the proposed RCT we will conduct a field-based experimental test of the hypothesis that, among overweight and obese midlife (ages 50-64) adults, adherence to PA programs will be improved when PA is explicitly recommended to be self-paced rather than prescribed at moderate intensity. This approach represents an important shift in mindset for those beginning a new program of PA: That is, PA need not be of a certain intensity in order to ?count?. If a self-paced recommendation is found to lead to better PA adherence among overweight and obese midlife adults, this could have implications for PA recommendations for that population.
Aim 1 : We will conduct an RCT comparing the effects of self-paced versus prescribed moderate intensity PA on PA behavior among low-active overweight and obese midlife (ages 50-64) adults (N=240). Based on procedures developed in our pilot, all participants will receive a 12-month intervention designed to help them overcome barriers to regular PA.53 The independent variable will be random assignment to either self-paced or prescribed moderate intensity PA. The primary outcome will be total volume of PA (frequency x duration x intensity) as measured by accelerometry at months 3, 6, 9, and 12. H1: A recommendation for self-paced PA will result in more PA (primary outcome) relative to prescribing moderate intensity PA based on current public health guidelines.12,54-56 Secondary outcomes include: (a) self-reported min/week of PA over the 12-month program, (b) fitness changes, and (c) weight changes at months 6 and 12.
Aim 2 : Using EMA, we will examine putative mediators of treatment effects based on our conceptual model (see Figure 1). H2: Self-paced PA will lead to a more positive affective response (primary mediator) and thus greater increases in PA behavior.37 Secondary mediators (analogous to secondary outcomes) will include: (a) perceived autonomy, and (b) perceived exertion (RPE).37 Other predictors of PA behavior will also be explored.
Improving adherence to physical activity (PA) programs is critical for overweight midlife adults (ages 50-64) in order to enhance weight management efforts and reduce risk of chronic disease and premature death. Current national PA recommendations, which call for PA of at least moderate intensity (64-76% of maximum heart rate), do not consider how people feel (i.e., pleasure or displeasure) while they are exercising, despite the fact that many overweight midlife adults find moderate intensity PA to be aversive. In this study we will compare the effects of an explicit recommendation for self-paced PA versus a traditional intensity-based exercise prescription (based on heart rate range) on PA behavior among previously low-active overweight midlife adults.
