The Reality Gap: Are We as Active as We Think?

There is a growing concern about the gap between how much physical activity we believe we're doing and how much we're actually engaging in. A study published in the International Journal of Behavioral Nutrition and Physical Activityby Schuna et al. (2013) sheds light on this issue using data from the 2005-2006 National Health and Nutrition Examination Survey (NHANES). The study compares self-reported physical activity and sedentary behaviors with those objectively measured by accelerometers, revealing a stark difference that challenges our current understanding of physical activity levels.

The research reveals that individuals who self-reported meeting the physical activity guidelines of at least 150 minutes of moderate-to-vigorous physical activity (MVPA) per week were, in reality, achieving only about 57 minutes per week when objectively measured. This finding highlights a significant overestimation of physical activity in self-reports. The discrepancy likely arises from the cognitive difficulties in recalling physical activity accurately and the ambiguous nature of terms like "moderate" and "vigorous" (Schuna et al., 2013).

Furthermore, the study shows that while those who reported higher levels of physical activity did engage in more activity as measured by accelerometers, their total sedentary time was not significantly lower than those reporting less activity. This suggests that even people who think they are active still spend a considerable amount of time being sedentary, which is concerning given the independent health risks associated with prolonged sedentary behavior.

The study also examined usual occupational/domestic activity (UODA) and leisure-time sedentary behavior (LTSB), revealing that adults who reported spending most of their day sitting or engaging in three or more hours of sedentary leisure time accumulated significantly less physical activity than those with more active daily routines. These findings underscore the importance of both the amount and the context of physical activity in determining health outcomes.

One of the innovative approaches of this study was to cross-classify individuals based on their self-reported MVPA, UODA, and LTSB. This method provided a more detailed view of physical activity patterns. For example, the group that reported high levels of physical activity, low sedentary time, and active occupational/domestic routines accumulated more than twice as many daily steps as the least active group. This approach offers a clearer picture of how different combinations of behaviors impact overall activity levels and emphasizes the limitations of relying on single, self-reported measures to predict health outcomes (Schuna et al., 2013).

While the study provides valuable insights, there are some limitations. The NHANES question on transportation-related MVPA did not specify that activities should last at least 10 minutes to be counted, potentially misclassifying participants. Additionally, the measure for UODA was not strictly occupational, potentially overlapping with leisure-time activities and confounding the results. Future research should aim to refine these measures and explore more accurate ways to capture physical activity and sedentary behaviors.

The findings of this study call into question the accuracy of self-reported physical activity data, which may not reflect actual behaviors. As we strive for better health outcomes, it is essential to base our public health guidelines on reliable, objective data. This will help us move beyond assumptions and more accurately assess and improve physical activity levels within the population.

Reference: Schuna, J. M., Johnson, W. D., & Tudor-Locke, C. (2013). Adult self-reported and objectively monitored physical activity and sedentary behavior: NHANES 2005-2006. International Journal of Behavioral Nutrition and Physical Activity, 10(126).