Engagement in regular physical activity is an important part of a healthy lifestyle. Research has shown that regular exercise is linked to the prevention of cardio-vascular disease, type 2 diabetes, cancer, hypertension, obesity, osteoporosis, and depression . The physical activity guidelines set forth by the Canadian government recommend that adults engage in a cumulative total of sixty minutes of moderate intensity physical activity (occurring in bouts of at least 10 minutes) every day . In addition to this, some research has shown that vigorous exercise can lead to health benefits above and beyond those offered by moderate intensity exercise. For example, the use of antidiabetic, antihypertenstion, and LDL-C-lowering drugs have been found to have an inverse relationship with vigorous physical activity . Furthermore, in a study examining the relationships between physical activity and fatness in adolescents, it was found that lower percent body fat was related to vigorous physical activity but not to moderate intensity physical activity . It appears that in order to achieve the health benefits associated with physical activity it is important to exercise regularly and at an appropriate intensity. Despite the vast amount of research that has demonstrated the link between physical activity and health, 63% of Canadians are not sufficiently active to obtain these health benefits . One factor that is thought to contribute to an individual's physical activity levels is his or her motivation to exercise. In fact, various types of motivation have been found to influence effort expended during exercise sessions as well as intentions to continue exercising .
Self-Determination Theory (SDT)  has been proposed as one way of looking at motivation. SDT is a general theory which has frequently been applied in the exercise domain. The SDT framework posits that human motivation lies along a continuum which represents varying degrees of autonomy. Autonomy refers to behaviors being self-determined, or freely initiated by the individual . The self-determination continuum is comprised of both intrinsic and extrinsic components. Intrinsic motivation occupies the most self-determined end of the continuum and involves motivation derived from the sheer pleasure and satisfaction of engaging in the behavior itself . An exerciser who is intrinsically motivated might swim, for example, because they enjoy the feeling of their body moving through the water. Four distinct behavioral regulations comprise the extrinsic part of the motivational continuum. These four regulations successively decrease in their degree of self-determination from autonomous regulations to controlling regulations. Integrated and identified regulations represent the more autonomous forms of extrinsic motivation. Integrated regulation is represented by an individual's belief that a behavior is an important part of his or her identity and is consistent with his or her personal values . An individual who demonstrates integration might go running because they believe they are 'a runner' and therefore running is consistent with their sense of identity. Identified regulation refers to being motivated to perform a behavior because it is personally significant and results in outcomes which are valued by the individual [6, 7]. For example, individuals might engage in resistance training because they know that weight bearing activities are important for bone health. Controlling regulations (introjected and external) occupy the less self-determined end of the motivational continuum. Introjected regulation represents the desire to obtain intrapersonal rewards (e.g., pride) or to avoid self-inflicted punishments (e.g., guilt or shame)  while external regulation refers to the desire to obtain external rewards or avoid punishments . An individual who exercises for external reasons might do so to appease their spouse or their physician. It is also possible that an individual will be amotivated. That is, they will engage in a behavior without feeling any motivation, or they will exhibit a complete lack of intention to perform a behavior. An individual's relative location along the self-determination continuum is determined by the degree to which he or she has achieved satisfaction of the basic psychological needs for competence, autonomy, and relatedness .
One important contention of SDT is that the external regulations and amotivation are less adaptive in nature while intrinsic motivation results in positive motivational consequences. Research has supported this contention with amotivation being linked to behavioral disengagement and negative psychological conditions . Furthermore, intrinsic motivation is associated with persistence at a task as well as psychological health and well-being . In an exercise context, research has examined individuals at various stages of exercise adoption and found that individuals with tendencies toward more regular exercise are more self-determined in their motivation .
In spite of these findings, it has been suggested that some people may persist at sport and exercise despite being extrinsically motivated . This suggestion can be highlighted by research examining the relationships between obligatory exercise and motivation. In a study involving regular exercisers it was found that individuals who are preoccupied with exercise, or who exercise at greater frequency, tend to score higher on identified regulation . Furthermore, individuals who experience negative emotional consequences (i.e., anger, depression) when they miss an exercise session tend to score highly on introjected regulation. In terms of exercise intensity, for individuals who show symptoms of exercise dependence, introjected regulation approached significance as a positive predictor of strenuous exercise behavior and identified regulation was found to be a positive predictor of strenuous exercise .
Using SDT as a context for examining the motivation of 598 male and female university students engaged in a variety of exercise classes (e.g., weight training, aerobics, swimming), it was found that students who were classified as 'more frequent exercisers' showed higher levels of intrinsic motivation and the autonomous forms of extrinsic regulation compared to 'less frequent exercisers' . A gender analysis revealed that females reported higher levels of intrinsic motivation and autonomous regulations while exercise behavior among males was more externally regulated and amotivated.
Further research examined the relationships between exercise regulations and various motivational consequences (i.e., behavioral intention, effort and importance associated with exercise participation, and current exercise behavior) among university students . Results revealed that identified regulation was the strongest predictor of each of the three exercise behaviors in both males and females. Intrinsic regulation was also found to predict effort and importance for males and females, as well as behavioral intention for females only. These findings were consistent with previous research and with SDT. Interestingly, it was found that introjected regulation was a positive predictor of all three motivational consequences for females only. This finding suggested that females may experience a sense of pride associated with exercise or some degree of guilt or shame if they do not exercise.
Overall, it appears that exercise-related motivation varies according to the amount of exercise an individual undertakes. Previous research has considered exercise behavior in several different ways, from intention to exercise and self-reported exercise frequency  to a measure including exercise intensity  and indicates that different types of behavior (e.g., exercise frequency and intensity) may be differentially regulated. Since SDT suggests that the regulations along the continuum are distinct, it is possible that they can be individually manipulated. If key motivational forces can be identified in regular exercisers and specific motivational deficits can be identified in less frequent exercisers, perhaps it is possible to target the most relevant types of motivation in order to increase exercise behavior among those who are insufficiently active. If this is the case, understanding the unique role that each regulation plays in exercise behavior has important practical implications for exercise interventions.
One main limitation to research regarding motivation to exercise has been that the three basic measures of exercise behavior, frequency, intensity and duration have not been investigated within a single study. Another limitation is the lack of a measure of integrated regulation. Many of the studies examining exercise motivation have used the Behavioral Regulation in Exercise Questionnaire (BREQ)  which does not measure integration. More recently, a measure of integrated regulation which is complementary to the BREQ has been developed . The inclusion of an integrated subscale allows for the full spectrum of motives to be measured which is important in order to gain a complete understanding of how individuals are motivated to engage in exercise. Therefore, the purpose of this study was to examine the relationships between three exercise behaviors (frequency, intensity, and duration) and the various behavioral regulations according to the SDT framework, including integrated regulation. Based on the contention of SDT that free-choice behaviors are most closely related to more self-determined motives, it was hypothesized that all three exercise behaviors would be most closely related to autonomous regulations and intrinsic motivation.