The purpose of this study is to investigate the relationships among self-determination factors, attitude toward the interaction with service providers, trust, exercise flow and adherence of personal training and group exercise program users. A comparative study was undertaken between the two types of services. The empirical analysis results suggest that participants' self-determination factors were positively related to exercise flow and that consumer-service provider interaction increased trust for the service providers. The antecedents of exercise flow differed according to the service types. While perceived relatedness enhanced the flow for personal training participants, perceived autonomy and competence influenced the flow of group exercise participants.