Fatigue is recognized as a significant and long-lasting effect of cancer treatment that influences quality of life. Although no studies to date have focused on exercise as an intervention to reduce fatigue and improve quality of life, previous studies have suggested exercise may have this effect. This proposal aims to use latent variable modeling to test the direct and/or indirect effects of exercise on fatigue and quality of life. Seventy-eight women with stage I-III breast cancer will be recruited in to this low-intensity progressive exercise study. Subjects will be followed for eight weeks using a 12-minute walk, Caltrac accelerometer monitoring, physical activity logs, Profile of Mood State fatigue-inertia and vigor-activity subscales, visual analogue scales of fatigue (twice daily), Quality of Life Index for patients with cancer, and Positive and Negative Affect Scales. Latent variable modeling will be used to test the fit of the measurement model.