Obesity and physical inactivity are poor prognostic indicators for breast cancer. Cardiorespiratory fitness (CRF) is a good predictor of survival for general population and for breast cancer survivors (BCS). CRF depends on genetic factors and on the PA performed by the individual. International organizations recommend at least 150 minutes per week of moderate-vigorous physical activity (MVPA). A limitation of physical activity (PA) research has been the use of self-reported measures. Some studies show that a minority of BCS are meeting the PA recommendations.