Regular exercise habits has proven to benefit human health. According to Self-determination Theory (SDT; Deci & Ryan, 1985, 2000; Ryan & Deci, 2002), self-determined motivation has been hypothesized to mediate the link between psychological need fulfillment and behavioral outcomes in exercise behavior. This study aimed to examine a) theoretically derived hypotheses about the relations between the latent constructs of psychological needs, self-determined motivation, physical activity behaviour and self-esteem b) the mediational role of self-determined motivation in association with psychological needs with exercise and self-esteem c) gender and age differences in the aforementioned associations.

In a Cross-sectional design, adult active members (N=1091) of an internet-based physical activity program between 18 and 78 years of age completed a test battery consisting of The Basic Psychological Needs in Exercise Scale (BPNES; Vlachopoulos & Michailidou, 2006), The Behavioral Regulation in Exercise Questionnaire-2 (BREQ-2; Markland & Tobin, 2004), Leisure-Time Exercise Questionnaire (LTEQ; Godin & Shephard, 1985) and five positively worded items from Rosenberg Self-Esteem Inventory (Rosenberg, 1989).

Need satisfaction predicted self-determined motivation which in turn predicted exercise and self-esteem as outcomes, especially for women and older adults. Self-determined motivation mediated the association between need satisfaction and outcomes, and this mediation effect was stronger for women and older adults.

The results confirm the hypotheses regarding mediation and contribute to the on-going discussion of the complexity of exercise motivation and behavioural and affective outcomes.  A valuable implication is that it seems important to consider moderating factors (e.g. gender and age) when designing exercise interventions. Such findings may not only bring important information to the more theoretical understanding of SDT based models of exercise but also serve as an informative compass or guide to increase adherence in exercise and lifestyle interventions for specific populations (e.g., younger women, older adults).