Inadequate physical activity levels are associated with a shorter lifespan because inadequate physical activity can increase an individual’s risk of developing chronic illnesses, like diabetes. Although the evidence is clear that increasing physical activity levels is important for preventing illness and premature mortality across the lifespan, do individual’s perceptions of their physical activity levels compared to others influence mortality? Prior work suggests that individual’s perceptions of their own health behaviors influences actual health behavior engagement 
leading to health outcomes.
A study recently published in Health Psychology examined whether adults’ perceptions of their physical activity levels predicted mortality. Data for this study came from the National Center for Health Statistics (NCHS), and included 61,141 participants across three nationally representative samples with follow-up time points up to 21 years later. One of the most important advantages of analyzing data from large-scale epidemiological studies is greater confidence in the accuracy of results by reducing the likelihood for error. Participants were asked to rate whether they perceived themselves as a lot more active, a little more active, as active, a little less active, and a lot less active than other people their same age. In addition, participants provided data on their actual physical activity levels via self-report or an accelerometer. Mortality was measured as death from any cause collected from the 2011 National Death Index. The authors chose to control for demographics variables, perceived health, number of illnesses, disability, mental health, smoking, body mass index, and actual physical activity levels in analyses to rule out alternative explanations for the effect.
This study found that, even after controlling for many variables influencing mortality, those who perceived themselves as a little more active or as active as others had an 8% increased likelihood of having died than those who perceived themselves as a lot more active than others. In addition, those who perceived themselves as a lot less active had an 18% increased likelihood of having died than those who perceived themselves as a lot more active. These results replicated in two additional samples, which provides evidence that these findings were not due to chance.
Taken together, this study supports a growing body of evidence that an individual’s perception of their own physical activity levels compared to others influences mortality. The authors suggest that perceptions predict mortality by influencing actual physical activity engagement. Future research will need to examine this mechanism. Given that physical activity interventions focus on increasing actual rates of physical activity, this study suggests that interventions may also want to target individual’s perceptions of their physical activity levels by informing people of their actual physical activity levels compared to others. Future research will need to assess the reasons why perceptions and social comparisons influence behavior.
Reference: Zahrt, O.H., & Crum, A.J. (2017). Perceived physical activity and mortality: Evidence from three nationally representative US samples. Health Psychology, 36, 1017-1025.