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2.6 Weight History

2.7.4 Physical Activity Barriers

Physical activity is an important behavior within the context of a behavioral weight loss intervention. When added to a calorie restricted diet, physical activity has been shown to enhance weight loss by approximately 20 to 25 percent compared to what is achieved through calorie restriction alone [103]. However, at the population level, engagement in a sufficient amount of physical activity appears to be less than optimal to impact body weight. Even within the context of a behavioral intervention not all participants initiate sufficient engagement in physical activity. Because of these considerations, it is important to explore individual perceptions of exercise barriers as they relate to weight loss in adults with obesity.

Examination of cross-sectional findings support that there is an inverse relationship between perceived physical activity barriers and physical activity engagement. For example, in a review of correlates of physical activity there is consistent evidence of higher barriers to physical activity being associated with lower activity levels independent of weight status [238]. This relationship is also observed for individuals with overweight or obesity. In behavioral weight loss interventions higher perceived physical activity barriers were inversely associated with moderate to vigorous physical activity at baseline [239] and at 6 months [235]. In addition Napolitano et al. observed that women with obesity and higher perceived physical activity barriers at 3 months reported 70 fewer minutes of physical activity compared to women with obesity with lower perceived barriers [240]. There is also evidence that decreasing perceived physical activity barriers within an intervention is associated with higher physical activity levels at 6 months [239, 241], 12 months [239], and 24 months [239].

Additionally, women with obesity were 10 times more likely to agree their weight makes physical activity more difficult compared to women who were normal weight [243]. At baseline prior to initiating a behavioral physical activity intervention, women with obesity reported significantly higher perceived physical activity barrier summary scores(60.8 ± 12.2) compared to overweight (56.7±13.3) or normal weight women(55.4±12.5) [240].

There is no consensus of whether perceived physical activity barriers are associated with weight loss within behavioral weight loss interventions or not. In a review by Teixeira et al., there was suggestive evidence based on two studies that perceived physical activity barriers at baseline were predictive of weight loss [36]. However, in an update to this initial review, it was found that perceived physical activity barriers were not predictive of weight loss, with there being limited studies exploring this psychosocial variable [38].

When examining individual studies, there is limited evidence to support baseline physical activity barriers as a predictor of weight loss. While Teixeira et al. found that baseline perceived physical activity barriers predicted weight loss success [39, 166], other studies have not replicated this. For example, two studies did not find baseline perceived physical activity barriers to predict weight loss at 4 months [208, 244]. In addition, while Gallagher et al. found a decrease in perceived physical activity barriers from baseline to 6 months to predict more weight loss at 6 months, they did not find baseline barriers to predict weight loss at 6 months [235]. Thus, additional research may be needed to address this discrepancy in findings regarding whether perceived physical activity barriers at baseline is predictive of subsequent weight loss.

Because of the potential inverse association between physical activity and perceived physical activity barriers in adults with obesity, it is important to consider whether behavioral interventions are effective at reducing these barriers. On average, behavioral weight loss

interventions produce a reduction in perceived physical activity barriers, although there is evidence of variation with response to interventions regarding when and how perceptions of physical activity barriers increase or decrease [208, 235, 239, 241, 245]. For example, Napolitano et al. observed that perceived physical activity barriers were lower in normal weight individuals compared with individuals with obesity at baseline and 12 months, but not significantly different at month 3, which corresponds to the end of the active phase of the intervention [240]. In another study that examined clinician determined physical activity barriers, during the weight loss phase physical activity barriers decreased; however, following the weight loss phase physical activity barriers appeared to increase during the maintenance period [246]. In addition, Call et al. demonstrated that despite a decrease in barriers through 12 months of active treatment, perceived physical activity barriers increased from 12 to 18 months and then remained stable through 24 months within a behavioral weight loss intervention [239]. Overall, interventions decrease perceived physical activity barriers, however this decrease appears to occur during the intensive intervention phase and it appears that perceived physical activity barriers increase following the most active phase of the intervention.

Individuals that reduce perceived physical activity barriers within behavioral interventions lose significantly more weight, with a decrease in perceived physical activity barriers being associated with short-term weight loss at 4 months [208, 240] and 6 months [235]. Additionally, Teixeira et al. found individuals who reduce their perceived physical activity barriers have greater weight loss at 12 months [247]. Moreover, this study reported that barriers to physical activity was more strongly associated with 12-month weight loss than other psychosocial measures that were examined [247].

There may be demographic factors that contribute to whether physical activity barriers are associated with weight status or weight loss, and a better understanding of their utility is warranted. Call et al. reported that being younger and white was associated with higher perceived physical activity barriers, although they found no differences between gender or BMI status [239]. In addition, variations in perceived physical activity barriers have been demonstrated across gender, race, education, and level of BMI [246, 248]. For example, Venditti et al. found that being female or having obesity was associated with higher clinician assessed physical activity barriers [246] while Stankevitz et al. found higher perceived time barriers to physical activity in white participants compared to other races [248]. Due to the variation of perceived physical activity barriers based on different demographics, it may be important to better understand physical activity barriers to facilitate more individualized behavioral weight loss interventions [249].

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