Obesity is commonly defined as a body mass index of 30 kg/m2or higher. Increasing rates of obesity in many countries represent a great challenge for public health. In the United States, for example, the rate of adult obesity exceeds 35%. Obesity is associated with increased risk of premature mortality resulting from chronic diseases (e.g., diabetes, cardiovascular and cerebrovascular disease, certain cancers), increased disability (e.g., knee osteoarthritis, chronic back pain, fatigue), and increased health care costs.
The etiology of obesity is multifactorial, comprising both genetic and epigenetic factors. While an increasing number of putative risk factors continually emerge (including such novel contributors as sleep deprivation and stress), the “big two” causal factors are diet and physical inactivity.
Obesity is of special interest to exercise professionals because obese individuals exhibit lower rates of physical activity (PA) participation and higher rates of nonadherence and drop-out than their normal-weight counterparts. However, the reasons behind this phenomenon remain unexplored, severely limiting the intervention options that are available to practitioners.
While most scientific organizations and public health agencies currently recommend a minimum of 30 minutes of moderate-intensity PA on 5 days per week for health maintenance in the general population, the recommended dose for weight management is more demanding. Specifically, most organizations recommend at least 60 minutes of activity per day to prevent weight gain and at least 60 to 90 minutes per day for the avoidance of weight regain in individuals who were previously overweight or obese.
Nearly all obese individuals report that they would like to weigh less (90% of men, 96% of women). Approximately two thirds report doing something in an effort to lose weight. Even of those obese individuals who say that they are doing something to lose weight, however, the percentage of them who report engaging in PA (approximately 61% of men, 56% of women) is lower than that in the general population.
The magnitude of the problem becomes more clearly evident when one examines how much PA obese individuals do. The percentage of those who do not meet the minimum recommended amount of PA for health approaches 80%. In 2000, according to Behavioral Risk Factor Surveillance System data, 21.3% of obese men and 15.9% of obese women trying to lose weight reported combining eating fewer calories with at least 150 minutes of PA per week. Only 6% of men and 3% of women reported combining eating fewer calories with at least 420 minutes of PA per week (i.e., 60 minutes per day on average). When activity is measured objectively via accelerometers, the percentage is even lower. In a 2009 study of 1,297 obese participants, which was conducted by Deborah Rohm Young and collaborators, only 1.7% were found to be active at least at a moderate intensity for at least 60 minutes per day. On average, the participants in this sample did only 12.8 minutes of moderate and 2.0 minutes of vigorous PA per day.
When considering the relationship between physical inactivity and obesity, most researchers and practitioners assume that causation is unidirectional: People who do less activity become obese. However, longitudinal studies from several countries have shown that, whereas the inactivity– obesity link is usually weak or nonexistent, the obesity–inactivity link is always robust.
This finding has several implications. First, it underscores the importance of efforts to address the growing problem of childhood obesity because it suggests that, once obesity develops, it becomes an important barrier to PA participation. Second, this finding shows that obese individuals face unique challenges in their efforts to become and remain physically active, beyond those faced by their normal-weight and even overweight counterparts.
Extensive evidence indicates that obesity is associated with significant declines in quality of life (QOL) and a range of mental health problems. Among obese youth, self-reported QOL has been found to be comparable to that of children and adolescents diagnosed with cancer. Shame and social isolation are presumed to be significant mediators for this effect. Among adults, epidemiological data indicate that obesity is associated with a 25% increase in the risk for mood and anxiety disorders. Longitudinal studies, such as the British Whitehall II study, have also shown that, while obesity predicts mental health problems, the case is at least as strong for the reverse order: Individuals with a higher number of mental health problems have a higher risk of becoming obese over time.
Possible Reasons for Physical Activity Avoidance
The reasons for the extremely low rates of PA participation among obese individuals are not fully understood. Based on preliminary evidence, the hypotheses that have emerged include the following. First, possibly due to media messages, many obese individuals begin activity regimens with unrealistically high weight loss expectations. When these expectations are violated, frustration ensues.
Second, a high number of obese individuals experience self-presentational concerns in the context of PA, resulting in social physique anxiety (SPA). Under the influence of this anxiety, several environmental cues, such as the presence of others or wall-to-wall mirrors, are interpreted as threatening. Third, perhaps as a result of prior negative experiences, a high percentage of obese individuals report negative or dysfunctional attitudes toward PA. Approximately 25% report feeling “too fat to exercise.” In turn, this perceived barrier is associated with feeling too shy or embarrassed and having a poor exercise identity. Fourth, several studies have found evidence of both explicit and implicit antifat bias among exercise, nutrition, and medical professionals, as well as obesity specialists. For example, exercise science students, on average, endorse statements such as “Fat people are physically unattractive” and “There is no excuse for being fat.” Fifth, a growing number of studies show that physiological and biomechanical problems associated with obesity contribute to making the exercise experience less pleasant. It has been found, for instance, that obese individuals experience more pain (possibly due to heavier impacts on knees and lower back), higher perceived exertion, more dyspnea, and more uncomfortable thermal sensations during exercise.
- Ball, K., Crawford, D., & Owen, N. (2000). Too fat to exercise? Obesity as a barrier to physical activity. Australian and New Zealand Journal of Public Health, 24(3), 331–333.
- Chambliss, H. O., Finley, C. E., & Blair, S. N. (2004). Attitudes toward obese individuals among exercise science students. Medicine and Science in Sports and Exercise, 36(3), 468–474.
- Ekkekakis, P., Lind, E., & Vazou, S. (2010). Affective responses to increasing levels of exercise intensity in normal-weight, overweight, and obese middle-aged women. Obesity, 18(1), 79–85.
- Kivimäki, M., Lawlor, D. A., Singh-Manoux, A., Batty, G. D., Ferrie, J. E., Shipley, M. J., et al. (2009). Common mental disorder and obesity: Insight from four repeat measures over 19 years: Prospective Whitehall II cohort study. British Medical Journal, 339,
- Young, D. R., Jerome, G. J., Chen, C., Laferriere, D., & Vollmer, W. M. (2009). Patterns of physical activity among overweight and obese adults. Preventing Chronic Disease, 6(3), A90.