Socioeconomic disparities in physical activity among Swedish women and trends over time - the population study of women in Gothenburg.

Objective: To explore secular trends in physical activity in relation to socioeconomic position in middle-aged women, with focus on whether the social gaps have become wider, narrower, or remain unchanged.

Design: Cohort comparisons between two representative samples of women, recruited in 1980-81 and 2004-05 as a part of the Population Study of Women in Gothenburg.

Setting: Gothenburg, the second largest city of Sweden, with ≈ 450 000 inhabitants.