The purpose of the present study was to examine motivations for participating in physical activity in an emerging adulthood sample, using Eccles et al.’s (1983) expectancy-value model. Of particular interest was how this model varied for individuals engaging in sports versus exercise. Three hundred and twenty eight undergraduate students completed questionnaires assessing expectancy beliefs, subjective task values, participation indicators as well as health outcomes. Model effectiveness varied as a function of both the activity itself as well as the specific participation indicator. For both sports and exercise activities, however, emerging adults appeared to be more driven by internal rewards (e.g., demonstrating competence, having fun) than by external incentives (e.g., attention and career goals). Findings of the present study partially support the use of the expectancy-value model in this research context, although future research might consider some revision to the measure, to better reflect motivations specific to physical activity engagement.