ABSTRACT
As indicated in previous chapters, genetic background plays a crucial role in determining an individual’s daily physical activity patterns; however, genetics is not the only factor driving physical activity. Like other behavioral phenotypes, physical activity is a complex behavior and is driven by various physiological variables not only influenced by genetics, but also, combined effects of genetics and environmental factors. When considering environmental influences on physical activity, the general thought is that common environmental factors, an example of which is our ‘built environment” or presence and ease of access to sidewalks, parks, trails, and recreational facilities, is an important factor in determining individual activity engagement. This thought, however, has yet to be supported by evidence in adults where physical activity has been measured objectively (13, 18, 49). Thus, ease of access to a gym or parks does not necessarily prompt an increase in physical activity among individuals. Less commonly considered are unique environmental factors that affect physical activity, defined as all individual-specific experiences (see Chapter 6). Such factors have been calculated to account for 8–52% of the observed interindividual variation in daily activity patterns (33, 62, 66, 71). The precise unique environmental factors that directly influence an individual’s physical activity are beginning to be studied, with work isolating factors including specific types of environmental chemicals and diet demonstrating a significant and detrimental effect of these factors on physical activity patterns. In this chapter, the purpose is to discuss two unique environmental influencers of the genetic regulation of activity and potential mechanisms (32) through which each are hypothesized to regulate activity.
