Inactivity Causes Excess Body Fat — Or Is the Reverse True?
From The Sports Medicine Bulletin
By Kathleen F. Janz, Ed.D., FACSM, and Soyang Kwon, Ph.D.
Given the health consequences for individuals and the economic burden of health care for society, the lack of physical activity and increased prevalence of obesity are major areas of interest for researchers, health practitioners and the public. There is substantial evidence that both the lack of physical activity and the rise in obesity contribute to poor health, independently of and synergistically with each other.
Physiologically, it makes sense that the lack of physical activity contributes to adiposity accumulation. Many epidemiologic studies have also shown the effect of inactivity on obesity phenotype. However, the role of adiposity on physical activity participation (reverse causation hypothesis) has been investigated less often. Understanding the potential effects of adiposity levels on physical activity has significant implications for designing physical activity intervention programs, even those not specifically aimed at preventing or reducing obesity. The reverse causation hypothesis implies a positive feedback loop, where becoming obese leads to physical inactivity which leads to becoming more obese – a pattern that may continue throughout life. The consequences of this loop could be particularly devastating for children due to the strong tracking of adiposity and the critical formation of attitudes, values and motor skills that takes place during childhood.
How can adiposity level negatively influence physical activity behaviors in children – especially given that the general population, including most children, is aware of the detrimental health consequences of obesity as well as the weight loss potential afforded by physical activity? (One might assume that being obese would be an excellent motivator for high levels of physical activity.) The reality is that obesity and physical activity behaviors exist in a complex bio-behavioral context. There is accumulating support for obesity-induced biomechanical and physiological changes and psycho-societal influences of obesity, which in turn, could act to suppress physical activity behaviors. For example, there is some evidence that obesity leads to musculoskeletal changes, decreased mobility, modification of gait patterns, changes in energy expenditure and, perhaps most importantly, decreased affect during moderate-intensity movement. That is, exercise doesn't feel the same if you are obese. Obesity has also been shown to decrease physical activity self-efficacy. In addition, obese children are more likely to be bullied and perceived as less athletic.