Investigators were interested in examining if seasonal (i.e., for 1 or 2 months per year) versus regular (year-round) exercise was related to risk of type 2 diabetes (outcome; yeso) among men and women who are at high risk for type 2 diabetes, but have not been diagnosed with type 2 diabetes (i.e., diabetes free). For this, the recruited and enrolled 960 study participants without type 2 diabetes and classified them as seasonal (exposed) or regular (non-exposed) exercisers based on responses to a physical activity questionnaire. Then, the study participants were followed up annually for 5 years and type 2 diabetes diagnosis was ascertained and recorded. What type of study design is this? randomized controlled trial ecological study prospective cohort study case-control study