Engaging in regular physical activity has yield a number of physiological and psychological benefits (U.S. Department of Health and Human Service, 1996). Although the links between regular exercise and health are well documented, many people are either sedentary or infrequently active to accrue these health benefits (Georgiadis et al., 2001). For example, UK national surveys indicated that 72 % of English; 69 % of the Northern Irish and 61% Scottish populations are highly inactive and are generally failing to meet current physical activity recommendations (Lowther et al., 2007). In their study, Haase et al. (2004) reported that leisure-time physical activity is below the recommended level in university students from 23 countries.
Researchers have interested in the reason of not engaging in physical activity and factors affecting the exercise behavior. Understanding why individuals do not participate in sufficient physical activity is complex and multifaceted-encompassing personal, interpersonal, environmental, and policy determinants (Lovell et al., 2010; Louw et al., 2012).
Body mass index (BMI) is one of the personal factors that may influence the exercise behavior of individuals. Previous studies indicated that BMI is related to changes in lifestyle variables such as exercise behavior and physical activity level (Dumith et al., 2007; LahtiKoski et al., 2002). BMI not only influence exercise behavior but it also influence the reason or motives of exercising (Vartanian and Shaprow, 2008).
Self-determination theory (SDT; Ryan and Deci, 2007) is a conceptual framework which is frequently used in exercise setting for studying motivation of exercise participants. According to SDT, motivational states range along a continuum in relation to the degree of self-determination or the extent to which the behavior is regulated by controlling aspects. Amotivation represents one end of the continuum and is a lack all intention to exercise or exercise without intent (i.e., they may "go through the motions"). On the other hand, the continuum lies intrinsic motivation, the most self-determined, or autonomous form of motivation and intrinsically motivated individuals engage physical activity for enjoyment and satisfaction. Extrinsic motivation is in the continuum between amotivation and intrinsic motivation (Ryan and Deci, 2000). Studies have validated the effect of managing the social-contextual variables proposed by SDT in the different exercise promotion setting (Edmunds et al. 2008; Fortier et al. 2007). Therefore, a number of SDT studies have been applied comprehensively in the field of BMI and behavioral regulations in exercise, and these studies have showed the efficiency of SDT to explain the psychological factors relevant to BMI (Hwang and Kim 2013; Williams et al., 1996). Research has shown that the degree of self-determined motivation has been linked with greater diminishment in BMI, and developed persistence at the 23-month follow-up within a weight loss program (Williams et al. 1996).
Importantly, not only behavioral regulations but also the feelings of exercisers such as dispositional flow and social physique anxiety have been influenced by BMI (Greenleaf, 2005; Hausenblas and Fallon, 2002). For example, Fredrickson and Roberts (1997) reported that body shame and anxiety reduce or disrupt awareness of internal bodily states and flow experiences; but less is known about the associations between BMI and optimal psychological states occurring in exercise setting. On the other hand, previous studies clearly reported that BMI influence social physique anxiety (Hausenblas and Fallon, 2002; Sabiston et al., 2005). Research has also shown that social physique anxiety was positively predicted by physical characteristics such as BMI (Haase and Prapavessis, 1998; Thogersen-Ntoumani and Ntoumanis, 2007).
Rising rates of unhealthy behavior (i.e. eating disorder and obesity) and declining physical activity levels have increased interest in understanding psychological factors that underlay these trends (Haskell et al.,
2007). Thereby, to reveal the relationship between the psychological characteristics (i.e. behavioral regulations, dispositional flow and social physique anxiety) and BMI is important in order to use this knowledge to design and implement health programming. Moreover, limited literature is available on the relationship between flow experiences in exercise and BMI. This paper also includes the flow experiences which have not yet to be well studied or understood within exercise psychology framework. In the exercise domain, exercise participation, motivational variables, flow experience and social physique anxiety continue to consistently hold a strong link with health behavior (Pan et al., 2009; Verplanken and Melkevik, 2008). There is a strong necessity for investigating exercise behavior and the role of these psychological characteristics in initiation and maintenance to exercise. Moreover this research would be useful for practitioners working in college health services and recreation centers to understand factors that have an influence on college students behavioral regulations, dispositional flow and social physique anxiety in exercise environments.
In sum, the overall purpose of this study is to examine psychological characteristics of exercisers (behavioral regulations, dispositional flow, and social physique anxiety) in terms of body mass index. It was hypothesized that self-determined exercise motivation (i.e. intrinsic motivation) and dispositional flow would be higher in normal and underweight participants. In contrast, it was expected that non-self-determined motivation (i.e. external and introjected regulation), and in particular amotivation and social physique anxiety would be higher in overweight and obese participants.
All questionnaires were administered to 1190 university students who participated voluntarily. Participants were determined in terms of stage of change in exercise. To be eligible for the study, respondents had to be categorized in the preparation, action or maintenance stages of exercise involvement. 782 exercisers ([n.sub.male] = 369; [M.sub.age] = 22.42 [+ or -] 2.27 and [n.sub.female] = 413; [M.sub.age] = 21.38 [+ or -] 1.96) were eligible to data analysis based on their stage of change in exercise. They were aged 17-30 years ([M.sub.age] = 21.87 years, SD= 2.17). On average, male exercisers...