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Medicine & Science in Sports & Exercise:
doi: 10.1249/01.mss.0000218137.25970.c6
APPLIED SCIENCES: Psychobiology and Behavioral Strategies

Psychosocial Factors Related to Physical Activity and Weight Loss in Overweight Women

GALLAGHER, KARA I.1; JAKICIC, JOHN M.1; NAPOLITANO, MELISSA A.2; MARCUS, BESS H.2

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Author Information

1Physical Activity and Weight Management Research Center, University of Pittsburgh, Pittsburgh, PA; and 2 Centers for Behavioral and Preventive Medicine, The Miriam Hospital and Brown Medical School, Providence, RI

Address for correspondence: John M. Jakicic, Ph.D., Department of Health and Physical Activity, Physical Activity and Weight Management Research Center, University of Pittsburgh, 140 Trees Hall, Pittsburgh, PA 15260; E-mail: jjakicic@pitt.edu.

Submitted for publication April 2005.

Accepted for publication December 2005.

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Abstract

Purpose: This study examined whether psychosocial factors related to physical activity in overweight, previously sedentary women were affected by a 6-month behavioral weight loss program. In addition, these psychosocial factors were examined across levels of weight loss and self-reported physical activity in response to a weight loss intervention.

Methods: Data from 165 overweight (body mass index (BMI) = 32.7 ± 4.2 kg·m2) women (age = 37.6 ± 5.5 yr) who participated in a comprehensive behavioral weight loss program that included behavioral education, moderate caloric restriction, and progressive home-based exercise were examined. Body weight was assessed at 0 and 6 months. Perceived benefits and barriers, physical activity self-efficacy, and physical activity processes of change were assessed at 0 and 6 months. Physical activity (minutes per week of at least moderate-intensity activity) was assessed using the 7-Day Physical Activity Recall at 0 and 6 months.

Results: The intervention resulted in increases in physical activity self-efficacy, behavioral processes of change, and several cognitive processes of change(P < 0.05). There was a reduction in expected barriers for physical activity (P < 0.05). Individuals with ≥ 10% weight loss reported higher levels of physical activity self-efficacy, greater use of behavioral strategies to elicit social support, and fewer barriers to physical activity than those with lower levels of physical activity and less weight loss (P < 0.05). Individuals reporting higher levels of exercise also reported higher levels of physical activity self-efficacy, greater use of behavioral strategies, and fewer barriers to physical activity than those individuals with lower levels of physical activity (P <0.05).

Conclusion: Targeting self-efficacy, behavioral strategies, and barriers in weight management programs may improve physical activity, which may result in improved weight loss in overweight adults.

Recent public health initiatives have been aimed at decreasing the prevalence of overweight and obesity in the United States (18). Despite these initiatives, prevalence rates continue to increase, and millions of Americans remain overweight and obese. Physical activity has been shown to be vitally important for preventing weight gain or enhancing weight loss and as such is an important component of behavioral weight loss programs (19,27). However, recent estimates indicate that only 45% of adults meet minimal recommended levels of physical activity that will improve health-related outcomes (4,5), defined as at least 30 min of moderate-intensity physical activity on most days of the week (20,24). Moreover, it appears that there is an inverse relationship between level of physical activity and body weight (13,19).

Engaging in physical activity has been shown to improve weight loss, with recent guidelines recommending approximately 60 min of moderate-intensity physical activity daily to maximize weight loss and to prevent weight regain(6,9,10,22). Therefore, it is important to understand the factors that influence physical activity in overweight individuals. Potential psychosocial factors that have been shown to be associated with physical activity participation include outcome expectations, perceived barriers, self-efficacy, and the processes of change(14,21). Previous research in the area of physical activity has shown that these variables change in response to a behavioral intervention. For example, Dunn et al. (7) examined changes in behavioral and cognitive processes of physical activity in individuals participating in a 6-month physical activity intervention, with the intervention based primarily on social-cognitive theory and the transtheoretical model. Results indicated that individuals who increased self-efficacy for physical activity, along with applying behavioral and cognitive strategies, were more likely to meet public health recommendations for physical activity. It is unclear whether similar results would be observed in individuals engaging in physical activity as part of a comprehensive weight loss program or whether psychosocial variables differ by magnitude of weight loss or achieved level of physical activity.

Therefore, the purpose of this study was to examine the following research questions in a cohort of overweight and obese women:

1. What is the effect of a comprehensive behavioral weight loss intervention that is designed to modify eating and physical activity behaviors on psychosocial variables that have previously been shown to influence physical activity?

2. What is the effect of varying levels of relative weight loss (< 5%, 5-9%, ≥ 10%) on psychosocial variables that have previously been shown to influence physical activity?

3. What is the effect of achieving varying levels of moderate-intensity physical activity (< 150 min·wk−1, 150-199 min·wk−1, 200-299 min·wk−1, or ≥ 300 min·wk−1) in a comprehensive behavioral weight loss intervention on psychosocial variables that have previously been shown to influence physical activity?

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METHODS

Subjects

A total of 201 overweight, sedentary healthy women were recruited using newspaper advertisements to participate in a behavioral weight loss intervention. The primary aim of the study was to examine the effect of varying doses and intensities of exercise on long-term weight loss and cardio respiratory fitness; the primary outcomes have previously been published (11). Females aged 21-45 yr with body mass index (BMI) between 27 and 40 kg·m−2 were eligible to participate in this study. Participants were excluded if they had medical limitations that would affect study participation, if they were pregnant or had been pregnant in the previous 6 months, or if they were taking any medication that would affect metabolism, body weight, or physiological responses to exercise (e.g., beta-blockers). Additional exclusion criteria included weight loss of ≥ 10 lb in the previous 12 months, participation in a commercial and/or medically supervised weight loss program in the previous 12 months, or regular participation in physical activity ≥ 3 d·wk−1 for at least 20 min·d−1. These weight loss and physical activity exclusion criteria were implemented so that focus of the intervention was on weight loss and increasing physical activity rather than maintaining a previously achieved weight loss or an existing level of physical activity. Written informed consent and medical clearance from their personal physician were obtained for all participants prior to initiating this study. All procedures were approved by the institutional review boards at the Miriam Hospital, Providence, RI, and the University of Pittsburgh. Baseline characteristics of participants are shown in Table 1.

Table 1
Table 1
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Intervention

The comprehensive behavioral weight loss intervention that was implemented in this study was group based, has been previously described by Jakicic et al. (11), and is based primarily on social-cognitive theory. The data presented in this study are for the initial 6 months of a 24-month intervention. Weekly group sessions were held during the first 6 months of the intervention. The content of the group sessions was based primarily on social cognitive theory and included strategies to reduce energy intake and increase energy expenditure. The group sessions lasted approximately 30 to 45 min, and the purpose was to address behavioral strategies to facilitate the adoption of eating and physical activity behaviors that would result in weight loss and improvements in cardiorespiratory fitness. The multidisciplinary intervention team consisted of individuals trained in psychology, nutrition, and exercise.

Modification of eating behaviors included instructions to reduce energy intake to 1200-1500 kcal·d−1 and dietary fat intake to 20% of total energy. As previously reported, dietary intake was reduced from approximately 2100 kcal·d−1 at baseline to approximately 1500 kcal·d−1 at month 6, with dietary fat decreasing from approximately 38% to approximately 28% across this same 6-month period (11). To facilitate the adoption of these recommendations, participants were provided with structured meal plans and were instructed to record their daily food choices, calories, and fat grams in a weekly diary that was reviewed by the interventionists.

The physical activity component of the intervention consisted of randomly assigning participants to one of four conditions based on both dose of structured activity (1000 vs 2000 kcal·wk−1) and intensity of the activity (moderate vs vigorous). Therefore, participants were assigned to one of the following groups: 1000 kcal·wk−1 at a moderate intensity, 1000 kcal·wk−1 at a vigorous intensity, 2000 kcal·wk−1 at a moderate intensity, or 2000 kcal·wk−1 at a vigorous intensity. The specific progression and components of this physical activity intervention have previously been published (11). All exercise was home based, and participants were instructed to engage in activities similar to brisk walking as the mode of exercise. As previously reported (11), walking was reported as the mode of exercise for 87.5% of the exercise sessions.

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Measurements

Body weight, BMI, physical activity, and psychosocial variables were measured at baseline and 6 months according to the following procedures.

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Body weight, height, and BMI.

Body weight was measured to the nearest 0.1 kg (0.25 lb) with subjects wearing a cloth hospital gown, without shoes on a calibrated balance beam scale. Height was measured to the nearest 0.1 cm using a calibrated wall-mounted stadiometer. BMI was determined by dividing body weight (kg) by height (m2).

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Physical activity.

Physical activity participation was determined using an interviewer-administered 7-day Physical Activity Recall (2). All interviewers were trained using a standardized protocol. This questionnaire determines the frequency and time spent in sedentary, light, moderate, hard, and very hard levels of physical activity over the previous 7-d period. Activities were classified into these intensity categories based on the METs provided in the compendium of physical activities (1). For the purpose of this study, physical activity that was consistent with the activity recommendations of the intervention was defined as the amount of time spent in activity that was of moderate intensity or greater over the 7-d period.

Psychosocial variables that have previously been shown to be correlated with physical activity were assessed at 0 and 6 months using the questionnaires presented below. Questionnaires were completed at home by the participant and returned to the investigators at the assessment visit.

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Physical activity self-efficacy.

Self-efficacy for exercise was assessed using the Physical Activity Self-Efficacy questionnaire developed by Marcus et al. (17). The five-item scale rates subject confidence regarding the ability to be physically active in various situations. Response options range from 0 (not at all confident) to 5 (extremely confident). Marcus et al. (17) report that this self-efficacy measure has demonstrated an internal consistency of 0.76.

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Physical activity decisional balance.

A 16-item scale was used to assess physical activity decisional balance (16), which is used to rate the importance of a variety of positive and negative statements regarding the pros and cons of engaging in physical activity. This rating was based on a five-point Likert scale with a rating of 1 referring to "not important at all" and a rating of 5 referring to "extremely important." The pros scale of the decisional balance questionnaire has demonstrated an internal consistency of 0.79, and the cons scale has demonstrated an internal consistency of 0.95 (16).

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Expected outcomes and barriers for habitual physical activity scale.

The Expected Outcomes and Barriers for Habitual Physical Activity Scale was developed and validated by Steinhardt and Dishman (23). Participants rated their agreement with statements related to barriers and benefits of physical activity on a five-point Likertscale ranging from 1 (strongly disagree) to 5 (strongly agree). Ratings were used to compute a total score for both perceived barriers and perceived benefits of physical activity. In addition, ratings were used to compute subscales for perceived physical activity barriers (time barriers, effort barriers, obstacles barriers) and perceived physical activity benefits (psychological benefits, body image benefits, health benefits).

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Physical activity processes of change questionnaire.

The Physical Activity Processes of Change Questionnaire was completed by participants to assess the strategies used to modify physical activity behavior (16). This 40-item scale rates the frequency of use for each strategy over the past month on a Likertscale ranging from 1 (never) to 5 (repeatedly). Specific questions are used to allow the physical activity processes of change to be separated into physical activity cognitive processes and physical activity behavioral processes subscales based on previously proposed scoring algorithms (17). The cognitive processes subscale consists of the following: increasing knowledge, warning of risks, caring about consequences to others, comprehending benefits, and increasing healthy opportunities. The behavioral processes subscale consists of substituting alternatives, enlisting social support, rewarding oneself, committing oneself, and reminding oneself (15).

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Statistical Analysis

All analyses were performed using Statistical Packages for the Social Sciences software (SPSS Version 11.0). Statistical significance was defined at P < 0.05 (two tailed) for all analyses. As described above, the data analyzed for this study were collected as part of a larger study to determine the effect of varying doses of exercise on weight loss in a comprehensive behavioral weight loss program. Changes from baseline to 6 months in physical activity, body weight, and psychosocial variables were assessed using two-factor (group × time) repeated-measures ANOVA to determine whether there were significant group main effects, time main effects, or group × time interaction effects based on randomized group assignment for this study. The time main effect was based on the assessment data collected at 0 and 6 months. The group main effect was based on the randomized group intervention. As described earlier, the intervention consisted of randomly assigning participants to one of four conditions based on both dose of structured activity (1000 vs 2000 kcal·wk−1) and intensity of the activity (moderate vs vigorous). Therefore, participants were assigned to one of the following: 1000 kcal·wk−1 at a moderate intensity, 1000 kcal·wk−1 at a vigorous intensity, 2000 kcal·wk−1 at a moderate intensity, or 2000 kcal·wk−1 at a vigorous intensity.

Correlation coefficients were computed to determine the relationship between weight loss and both baseline and 6-month psychosocial variables using Pearson product-moment correlations. In the event of skewed data, Spearman rank order correlations were computed. To examine the relationship between weight loss and psychosocial parameters assessed at 6 months while controlling for baseline psychosocial data, partial correlation coefficients were computed.

Data were analyzed to determine the effect of the magnitude of weight loss on psychosocial variables. Participants were grouped based on weight loss achieved (< 5%, 5-9%, and ≥ 10%). These criteria are consistent with clinical recommendations for magnitude of weight loss that appears to be related to improvements in health-related outcomes (19) and the average weight loss achieved within a behavioral weight loss intervention (27). Repeated-measures ANOVA (group × time) were performed to detect differences in psychosocial variables based on magnitude of weight loss. When significant main effects were noted, Duncan post hoc analyses were performed to explore differences in group means.

Data were also analyzed to determine the effect of self-reported exercise participation on psychosocial variables. Spearman rho correlation coefficients were computed for the relations between 6-month physical activity and the psychosocial variables measured in this study. Moreover, 6-month physical activity was categorized into four groups that corresponded with current physical activity guidelines. These groups were 1) not meeting any recommendations for physical activity (< 150 min·wk−1), 2) meeting the American College of Sports Medicine/Center for Disease Control (ACSM/CDC) recommendations (150-199 min·wk−1), 3) following ACSM guidelines for sufficient physical activity to achieve weight loss (200-299min·wk−1), and 4) meeting the Institute of Medicine's recommendations for physical activity for weight loss (≥ 300 min·wk−1). A repeated-measures ANOVA (group × time) was performed to detect differences in psychosocial variables based on level of actual exercise participation.

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RESULTS

A total of 201 women were randomized to participate in this study, and 192 subjects completed 6 months of participation. Reasons for attrition included lack of interest (N = 5), pregnancy (N =3), and relocation (N = 1). For the present study, missing or incomplete data on variables of interest were also excluded from analyses, which included missing 6-month data for measures of physical activity (N =10), physical activity self-efficacy (N = 22), physical activity decisional balance (N = 24), expected outcomes and barriers for habitual physical activity (N = 27), and physical activity processes (N = 32). Therefore, complete data from 165 subjects were analyzed. Subject characteristics are shown in Table 1. Comparison of baseline demographic data showed that subjects with complete data were significantly older than subjects with missing data, with no additional difference in demographic characteristics being observed (data not shown). Moreover, there was no significant difference in the number of subjects with complete data based on initial randomized group assignment.

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Intervention effects on psychosocial factors.

Data were analyzed to determine whether there were significant differences for the variables of interest for this study based on randomized group assignment. The results showed no significant differences in baseline characteristics for age, weight, or BMI between subjects randomly assigned to each of the intervention groups. In addition, the results of a two-factor repeated-measures (group × time) ANOVA showed no significant differences between the intervention groups across the 6-month intervention period for body weight or physical activity. Because no significant group differences were found, data presented in Table 1 are collapsed across all intervention groups. Results showed a significant decrease in bodyweight of 8.69 ± 4.74 kg, with moderate- to vigorous-intensity exercise increasing by 150.33 ± 314.24 min·wk−1 (P < 0.01 for time main effect).

A series of repeated-measures ANOVA (group × time) revealed no difference in the pattern of change in the psychosocial variables between intervention groups across the 6-month intervention period. Overall, physical activity self-efficacy increased from baseline to 6 months (P <0.01 for time main effect). However, decisional balance showed no significant change across the 6-month intervention (P > 0.05 for time main effect). With respect to expected outcomes for physical activity, psychological benefits were the only variable to increase significantly from baseline to 6 months (P < 0.05 for time main effect). There were significant decreases (P < 0.05 for time main effect) in the expected barriers for physical activity (time barriers, effort barriers, obstacle barriers, and total barriers) across the 6-month intervention period (Table 2).

Table 2
Table 2
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There was a significant increase in physical activity behavioral processes across the 6-month intervention (P < 0.01 for time main effect), with no significant group main effect. In addition, there was a significant increase in all of the subscales for the physical activity behavioral processes (substituting alternatives, enlisting social support, rewarding oneself, committing oneself, and reminding oneself) (P < 0.01 for time main effect, see Table 2). While there was no change in physical activity cognitive processes, there were significant improvements in the increasing knowledge and increasing healthy opportunities subscales (P < 0.01). However, the caring about consequences to others subscale significantly decreased over the 6-month intervention (P <0.05 for time main effect).

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Relationship between 6-month weight loss and psychosocial variables.

Correlations between weight loss and psychosocial variables are presented in Table 3. Correlations between 6-month weight loss and baseline psychosocial variables indicated that image benefits (r = 0.15) were the only variable that was significantly correlated with weight loss (P < 0.05). However, 6-month weight loss was significantly correlated with 6-month scores for physical activity self-efficacy (r = 0.30) and physical activity decisional balance (r = 0.16). Weight loss at 6 months was inversely related to 6-month subscales of the expected barriers for physical activity: time barriers (r = −0.21), effort barriers (r = −0.29), obstacle barriers (r = −0.25), and total barriers (r = −0.31) (P < 0.05). In addition, there were significant relationships between weight loss and behavioral processes (r = 0.17) and the substituting alternatives (r = 0.16), enlisting social support (r = 0.19), and committing oneself (r = 0.17) subscales (P < 0.05). Partial correlations were computed for weight loss and psychosocial variables at 6 months, while controlling for baseline scores on these same psychosocial parameters (Table 3). These analyses revealed significant relationships between 6-month weight loss and 6-month values of physical activity self efficacy (r = 0.29) and physical activity decisional balance (r = 0.15) (P < 0.05), and an inverse correlation with each of the subscales of expected barriers for physical activity (Table 3). Partial correlations revealed significant correlation coefficients between 6-month weight loss and 6-month behavioral processes (r = 0.20), and the subscales of substituting alternatives (r = 0.19), enlisting social support (r = 0.17), and committing oneself (r = 0.20), and reminding oneself (r = 0.14) (P < 0.05).

Table 3
Table 3
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Psychosocial variables by weight loss.

The measured psychosocial variables were examined across the tertiles of percentage weight loss achieved following the 6-month intervention (< 5%,5-9%, and ≥ 10% weight loss). The weight loss groups did not differ on baseline measures for physical activity self-efficacy, physical activity decisional balance, physical activity processes, and expected outcomes and barriers for physical activity.

Results following the 6-month intervention based on weight loss achieved are shown in Table 4. Results following the 6-month intervention showed that physical activity self-efficacy was significantly lower in the < 5% weight loss group compared with the ≥ 10% weight loss group (P < 0.05). In addition, total barriers and effort barriers were significantly lower in the ≥10% weight loss group following the 6-month intervention compared with the < 5% and 5-9% weight loss groups (P < 0.05), with the ≥ 10% weight loss group also reporting fewer obstacle barriers than the < 5% weight loss group (P < 0.05). Moreover, the ≥ 10% weight loss group reported a higher score for enlisting social support following the 6-month intervention compared with the < 5% weight loss group (P < 0.05). There were no significant differences between the weight loss groups (< 5%, 5-9%, ≥ 10%) for 6-month scores for physical activity decisional balance, expected outcomes for physical activity, cognitive processes, or the remaining behavioral processes (Table 4).

Table 4
Table 4
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Relationship between 6-month physical activity and psychosocial variables.

Correlations were computed between physical activity participation at 6 months and the psychosocial variables measured in this study. Because physical activity data were skewed, Spearman rho correlation coefficients were computed to assess these relationships. There were no significant correlation coefficients between any of the baseline psychosocial variables and 6-month physical activity. However, 6-month physical activity was significantly correlated with 6-month physical activity self-efficacy (r = 0.30, P < 0.05) and 6-month physical activity decisional balance (r = 0.18, P < 0.05). Significant correlation coefficients were also computed for the relationships between 6-month physical activity and the 6-month behavioral processes score (r = 0.22, P < 0.01), along with the behavioral processess ubscales for substituting alternatives (r = 0.02, P < 0.01), enlisting social support (r = 0.17, P < 0.05), and reminding oneself (r = 0.23, P < 0.01). There was a significant inverse correlation coefficient for the relationship between 6-month physical activity and time barriers reported following the 6-month intervention (r = −0.17, P < 0.05).

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Psychosocial variables by level of physical activity participation.

As described earlier, 6-month exercise participation was categorized into four groups based on minutes of moderate- to vigorous-intensity physical activity per week (< 150 min·wk−1, 150-199 min·wk−1, 200-299 min·wk−1, ≥ 300 min·wk−1). Interestingly, 67% of subjects classified into the < 150 min·wk−1 group were initially randomly assigned to the 1000 kcal·wk−1 exercise groups, whereas 67% of subjects classified into the ≥ 300 min·wk−1 group were initially randomly assigned to the 2000 kcal·wk−1 groups. Data were analyzed using one-way ANOVA to examine whether there were significant baseline differences in psychosocial variables between the four groups based on minutes of moderate- to vigorous-intensity physical activity. There was no significant difference between the groups at baseline for physical activity decisional balance, expected outcomes for physical activity, expected barriers for physical activity, cognitive processes, physical activity self-efficacy, or behavioral processes.

Data were analyzed using a one-way ANOVA to assess potential differences in the psychosocial variables at the 6-month assessment period between the groups based on minutes of moderate- to vigorous-intensity physical activity, with results presented in Table 5. Because of a significant effect for physical activity self-efficacy, Duncan post hoc analyses were performed, which revealed significantly lower levels for individuals in the < 150 min·wk−1 group compared with the other groups (P < 0.001).

Table 5
Table 5
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Analysis of expected barriers for physical activity revealed significant differences between the groups for total barriers, effort barriers, and obstacle barriers (Table 5). Posthoc analysis indicated that at 6 months, both total barriers and effort barriers were significantly greater in the < 150 min·wk−1 group compared with the other groups (P < 0.05). When compared with the 150-199 min·wk−1 group, obstacle barriers were significantly greater in the < 150 min·wk−1 group and ≥ 300 min·wk−1 group (P <0.05). There were no significant differences between the groups for physical activity decisional balance or expected outcomes for physical activity measured following the 6-month intervention period (Table 5).

Analysis of physical activity processes of change indicated no differences between exercise groups for the cognitive processes or the subscales of cognitive processes. Results showed that behavioral processes were significantly lower in the < 150 min·wk−1 group compared with the 200-299 min·wk−1 and ≥ 300 min·wk−1 groups, and this pattern was also shown for the subscales of substituting alternatives and committing oneself (P < 0.05). The subscale of reminding oneself was significantly lower in the < 150 min·wk−1 group compared with all other groups (P < 0.05). In addition, individuals in the 200-299 min·wk−1 group reported greater levels on the enlisting social support subscale compared with the < 150 min·wk−1, 150-199 min·wk−1, and ≥ 300 min·wk−1 groups (P < 0.05). These data are presented in Table 4.

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DISCUSSION

The primary purpose of this study was to examine the effect of a comprehensive behavioral weight loss program on psychosocial variables that have previously been shown to influence physical activity. While other studies have examined the effect of physical activity based behavioral interventions on these psychosocial outcomes, this study examined these parameters within the context of a comprehensive behavioral weight loss program. The results of this study provide an important contribution to the scientific literature because of the known benefits of adequate levels of physical activity on improved weight loss outcomes (10-12) and chronic disease risk factors (8,26). Thus, it is important to identify factors that result in improved physical activity participation in this population.

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Intervention effects on psychosocial factors.

The intervention for this study was based primarily on social-cognitive theory and incorporated numerous strategies to enhance weight loss behaviors, which included physical activity and eating behaviors. These strategies included but were not limited to problem solving, goal setting, stimulus control, relapse prevention, and self-monitoring. As shown in Table 2, this intervention resulted in improvements in many of the psychosocial parameters measured in this study including physical activity self-efficacy, all behavioral processes of change (substituting alternatives, enlisting social support, rewarding oneself, committing oneself, and reminding oneself), and three of the five cognitive processes of change (increasing knowledge, caring about consequences to others, and increasing healthy opportunities). These results are similar to other studies that have reported improvements in physical activity self-efficacy and both behavioral and cognitive processes of change in response to a behavioral intervention focusing on increasing physical activity (7,14). Thus, it appears that overweight and obese adults respond in a similar manner on these psychosocial outcomes to what has been observed for normal-weight individuals, which may indicate that strategies for improving physical activity participation are not necessarily influenced by demographic characteristics such as body weight.

This study also showed that the behavioral intervention resulted in a reduction in the expected barriers to physical activity (see Table 2). However, aside from an increase in psychological benefits (P < 0.05), the intervention did not result in improvements in the expected image benefits or health benefits that can be achieved from physical activity (Table 2). This may be a result of barriers to physical activity rather than a lack of knowledge regarding the benefits of physical activity influencing the adoption and maintenance of this behavior. Moreover, 96.4% of the subjects in this study rated the benefits of physical activity between a score of 3 and 5 (1 = strongly disagree that the outcome was a benefit of physical activity; 5 = strongly agree that the proposed outcome was a benefit of physical activity). Thus, most individuals were aware of the potential benefits of physical activity, which may limit the magnitude of improvement that can result from the intervention. This may suggest that interventions should focus primarily on the barriers to physical activity rather than on further increasing the knowledge of participants regarding the potential benefits of physical activity.

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Weight loss and exercise effects on psychosocial factors.

This study examined relationships between psychosocial variables at baseline and 6 months with 6-month weight loss (Table 3). Results indicate that how an individual scores on these variables at the beginning of an intervention does not appear to relate to degree of weight loss achieved during the first 6 months. However, higher levels of physical activity self-efficacy, physical activity decisional balance, and several behavioral processes of change at 6 months were related to the greatest weight loss. In addition, reported barriers to physical activity at 6 months were inversely correlated with weight loss at 6 months, suggesting that individuals reporting fewer barriers to physical activity were able to achieve the greatest weight loss. Therefore, focusing interventions to increase physical activity self-efficacy, increase the use of selected behavioral strategies, and decrease barriers to physical activity may improve weight loss outcomes. However, the significant correlation coefficients in this study were of a moderate magnitude, which could affect the generalizability of these findings and therefore should be interpreted with caution.

As shown in Table 5, individuals who participated in < 150 min of moderate-to vigorous-intensity physical activity had significantly lower self-efficacy and reported using fewer behavioral processes than individuals who reported higher levels of physical activity. These findings are consistent with other studies that have measured physical activity self-efficacy (3,7) and suggest that this variable may be an important predictor of physical activity adoption. For example, Lewis et al. (14) reported that most physical activity interventions resulted in improvements in behavioral processes, which in turn were related to increases in physical activity participation. Moreover, Calfas et al. (3) reported that behavioral strategies, such as goal setting, enlisting social support, and self-efficacy were significantly associated with the level of physical activity. These results are similar to those reported by Dunn et al. (7), who showed that individuals who increased their use of behavioral strategies such as substituting alternatives, enlisting support, and committing oneself were more likely to meet the CDC/ACSM recommendations of ≥ 150 min of moderate-intensity physical activity per week. When physical activity self-efficacy and behavioral processes were examined based on the magnitude of weight loss achieved following the 6-month intervention, individuals achieving weight loss that was ≥ 10% of initial body weight reported higher levels of self-efficacy compared with those achieving <5% weight loss (Table 5). In addition, individuals achieving ≥ 10% weight loss reported use of more behavioral strategies to enlist social support than individuals achieving< 5% weight loss (Table 5). Thus, identifying and targeting overweight and obese individuals who have lower physical activity self-efficacy and who do not report the use of specific behavioral strategies to elicit social support may help to improve physical activity adoption and maintenance, which may improve weight loss in overweight and obese adults.

It is interesting to note that although cognitive processes such as increasing knowledge, caring about consequences to others, and increasing healthy opportunities improved over the 6-month intervention (Table 2), these cognitive processes did not differ between individuals grouped according to their level of physical activity (Table 5). A similar pattern was shown when participants were grouped based on weight loss achieved (Table 4). This finding is not unique to this study, as previous studies have reported similar results (14,21). This may be a result of cognitive processes (Tables 2-5) affecting whether an individual begins to engage in an intervention targeting physical activity, whereas the behavioral processes (Tables 2-5) may be most important once the individual is actively engaged in the intervention to modify physical activity behaviors (14). Thus, targeting cognitive processes may be most effective for individuals in the precontemplation or contemplation stages of changes, whereas behavioral processes may be most effective for individuals in the action and maintenance stages of change, and this may warrant further investigation to develop an explanatory model for physical activity interventions for overweight and obese adults.

This study also showed that individuals who participated in ≥ 150min of moderate- to vigorous-intensity physical activity per week or who achieved ≥ 10% weight loss reported fewer barriers to physical activity at 6 months than those participating in lower levels of physical activity or achieving less weight loss (Tables 4 and 5). This may have contributed to the higher levels of physical activity observed in these groups, which in turn may have contributed to the greater magnitude of weight loss. However, it should be noted that even those individuals who reported higher levels of activity or achieved greater weight loss did report at least some barriers to physical activity. For example, individuals who reported ≥ 300 min·wk−1 of moderate- to vigorous-intensity physical activity also reported more obstacle barriers than those individuals reporting 150-199 min·wk−1 of physical activity. Obstacle barriers include factors such as bad weather, lack of facilities, and family obligations. However, these barriers did not appear to have a negative impact on physical activity participation in this group, whereas these obstacle barriers may have negatively affected physical activity participation in those individuals reporting < 150 min·wk−1 of physical activity (Table 5). Thus, it may be possible that although these obstacles barriers were present, the ≥ 300 min·wk−1 group was able to overcome these barriers, but the < 150 min·wk−1 group was unable to implement strategies to address these barriers. Future research should examine how reported barriers to physical activity affect behavior and how to best target interventions at the barriers that appear to have a negative impact on behavior.

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Limitations and future directions.

This study is not without limitations. For example, the outcome variables were examined during the initial 6 months of the intervention. Thus, they only provide information regarding the adoption of physical activity during this period. However, examining these parameters beyond this initial period may provide valuable information regarding the importance of these psychosocial factors in the maintenance of physical activity and the impact on long-term weight loss in overweight and obese adults. This study only included women, and therefore it is unclear whether similar results would be observed in men. It is also important to note that this study examined the outcomes in the context of a comprehensive behavioral weight loss program that targeted changes in both physical activity and eating behaviors to achieve weight loss. Future studies should examine whether a similar pattern of results is observed in overweight and obese adults when the target of the intervention is physical activity behavior rather than weight loss. Physical activity was measured using a self-report questionnaire that has been shown to provide a valid and reliable assessment of physical activity (25). However, future studies may consider incorporating objective measures of physical activity such as accelerometry, HR monitors, and pedometers into the intervention when assessing physical activity.

The results of this study may also have implications for future interventions. For example, it appears that improving self-efficacy for physical activity and reducing barriers to physical activity are associated with improved physical activity participation and improved weight loss. Moreover, selected behavioral processes appear to be important for improving both physical activity and weight loss (Tables 4 and 5). Therefore, tailoring interventions to affect these psychosocial factors may prove to have a positive influence on increasing physical activity and improving weight loss in overweight and obese adults. Future studies are needed to examine the most appropriate method of tailoring interventions in this manner.

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SUMMARY

In summary, this study showed that psychosocial parameters that may have an impact on physical activity were affected by a comprehensive weight loss program for overweight and obese women. These findings are similar to those that have been reported for interventions that targeted physical activity as the outcome rather than both physical activity and eating behavior for weight loss. Moreover, individuals with higher levels of exercise and greater magnitudes of weight loss reported higher levels of physical activity self-efficacy, greater use of behavioral strategies, and fewer barriers to physical activity than those individuals with lower levels of physical activity and less weight loss. These findings are important for interventions targeting overweight and obese adults because of the demonstrated link between higher levels of physical activity and improvements in weight loss outcomes. Thus, interventions should focus on addressing these factors within comprehensive behavior weight loss programs to increase physical activity and potentially improve weight loss outcomes.

This study was supported by grant HL64991 from the National Institutes of Health and the National Heart, Lung, and Blood Institute. Additional support is provided from the National Institute of Diabetes and Digestive and Kidney Diseases (DK58002) and the Obesity/Nutrition Research Center at the University of Pittsburgh P30 (DK46204). The authors acknowledge the contribution of the staff of the Weight Control and Diabetes Research Center at the Miriam Hospital and the Physical Activity and Weight Management Research Center at the University of Pittsburgh for their assistance with this project.

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Keywords:

PHYSICAL ACTIVITY; OBESITY; SELF-EFFICACY; BARRIERS; PROCESSES OF CHANGE

©2006The American College of Sports Medicine

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