Exercise Trajectories and Current Exercise and Risk of Breast Cancer: a Cohort Study of 325,953 Women Who Participated in BreastScreen Norway

The purpose of the study was to elucidate life-course and current exercise levels among women aged 50–69 who participated in BreastScreen Norway during the period from 2006 to 2015, and to estimate the risk of breast cancer based on exercise trajectory classes and current exercise level. Self-reported data from 325,953 women were utilized for descriptive and exploratory analyses. Retrospective information about exercise levels at ages 15–19, 20–29, 30–39, and 40–49 was used to establish exercise trajectory classes, while reported exercise at ages 50–69 was considered as current activity. Hazard Ratios (HR) with 95