Objective: Examine differences in physical activity (PA) constraints experienced as freshmen among college upperclassmen based on sex, race/ethnicity, adiposity, and fitness. Participants and methods: Upperclassmen (n = 524) from self-reported demographics, PA, subjective changes in PA, and freshman PA constraints via an online survey, and had adiposity and predicted aerobic fitness objectively assessed. Results: Self-reported reductions in PA since high school and freshmen year were associated with a lack of motivation as a freshman, lower current PA levels, and poorer aerobic fitness compared to those who maintained or increased PA. Women were less active than men and reported greater constraints, while non-Hispanic white students had greater vigorous PA than minority students. Multiple regression analyses revealed that motivation constraints predicted PA regardless of sex and race/ethnicity. Conclusions: Findings highlight the importance of college administrators and health promoters alleviating freshman PA constraints, particularly among women, to promote the adoption of an active lifestyle.