For example, the main biological mechanism linked to physical activity and its potential benefit in BC is that it can decrease estrogen concentrations, particularly estradiol and sex hormone-binding globulin (SHBG) [53]; increase the length of menstrual cycles; and reduce ovulation in premenopausal women with high levels of physical activity [52,54], which it could be related to BC molecular subtypes with hormone receptors. This evidence concerns the gene NR4A1 and breast cancer.