Exercise Intervention in Women With Metastatic Breast Cancer

* Participants will be randomized to one of two groups. Study participants assigned to Group A will immediately participate in a 16-week exercise program, and participants assigned to Group B will wait 16 weeks before taking part in an exercise program. * Before beginning the exercise program (Group A) or waiting period (Group B), participants will undergo a series of tests to measure exercise capacity, fatigue level and quality of life. They will be asked to complete a series of questionnaires and meet with an exercise physiologist and undergo a treadmill test designed to measure physical fitness in patients with a chronic illness. The participant will complete the questionnaires again 8 weeks after enrolling in the protocol and will complete one final set and undergo a second treadmill test after the 16-week study period has ended. * Participants in Group A will be given a 16-week gym membership, as well as a heart rate monitor and a pedometer. They will meet with an exercise physiologist, who will design an exercise program for each participant. Participants will meet with the exercise physiologist weekly for 4 weeks, then once per month for the duration of the study. The target exercise goal will be 150 minutes of moderate-intensity exercise each week. * Participants will be given an exercise journal to record the minutes of cardiovascular exercise and steps taken each day. These journals will be reviewed by the exercise physiologist each week. * Participants in Group B will be allowed to exercise as much as they wish during the first 16-weeks of their time on the study, but they will not be given a formal exercise plan or a gym membership until the completion of the 16-week waiting period. During this time, they will also complete questionnaires at the time of study entry, 8 weeks after enrolling, and at the end of 16 weeks. After the 16-week delay period has passed, participants in Group B will be given a pedometer, heart rate monitor and 16-week gym membership. They will also meet with an exercise physiologist weekly for one month, and the exercise physiologist will design an individualized exercise plan for these participants.