Inclusion Criteria:
1. Age ≥ 18 years
2. Diagnosis of DCIS or stage I, II, or III breast cancer 3 Planned to initiate an AI
1. Post- menopausal defined as ≥ 60 years of age, prior bilateral oophorectomy, or age over 50 and absence of any menstrual periods in the last 12 months, or FSH and estradiol in the menopausal range
2. Premenopausal patients receiving chemical ovarian suppression are allowed
3. Prior aromatase inhibitor use (if this is a second primary, for example) is allowed as long as it has been more than 12 months
4. Prior tamoxifen is allowed if switching to an aromatase inhibitor, as long as it has been 28 days between last tamoxifen dose and the baseline procedures (per the half-life of tamoxifen)
4\. Completion of all primary therapy for breast cancer, including surgery, radiation, and chemotherapy. Patients must be ≥ 21 days from chemotherapy completion and ≥14 days from radiation completion. Ongoing HER2 targeted therapy with trastuzumab or pertuzumab, or TDM1 is allowed. Ongoing therapy with abemaciclib per standard of care is allowed.
5\. Baseline T score \> - 2.5 on DXA 6. Body weight less than 275 lbs., as dictated by the weight limit for the LIV platforms 7. ECOG performance status of 0-2 at the time of study enrollment 8. Informed consent and authorization of the release of health information must be obtained according to institutional guidelines 9. Physically able to stand unassisted for 10 minutes at a time 10. Currently not participating in regular exercise (defined as less than 90 minutes of moderate to vigorous exercise per week measured by the RPAQ questionnaire)
Exclusion Criteria:
1. Unwilling to co-enroll onto the companion FIT core study (IRB study #1707550885)
2. Diagnosis of other disorder affecting bone function or turnover, such as Paget's disease, renal osteodystrophy, parathyroid disorders, vitamin D deficiency/osteomalacia, chronic renal disease (Cr \> 1.4)
a. Vitamin D will be checked during screening. Patients with Vit D \< 20 can be enrolled if supplementation is initiated per the treating physician.
3. Prior history of non-traumatic, fragility bone fracture
4. Any muscle or neuromuscular disorder affecting muscle function, such as muscular dystrophy, myositis, or amyotrophic lateral sclerosis
5. Use of bisphosphonates or denosumab within the prior 12 months
6. History of retinal detachment
7. Current or planned pacemaker
8. Current or planned cochlear implant
9. Any condition precluding power protocol participation (i.e. riding a stationary bicycle), including: NYHA class III or IV congestive heart failure, uncontrolled angina, myocardial infarction in the prior 12 months, orthopedic surgery in the previous 6 months or plans for orthopedic surgery during the study period, chronic uncontrolled pulmonary conditions such as uncontrolled asthma (symptoms \> 2 days/week) or dyspnea requiring oxygen, symptomatic peripheral vascular disease, or any other comorbidity that would interfere with the ability to complete and comply with the protocol in the opinion of the investigator
10. Metastatic breast cancer
a. History of prior treated malignancies, other than breast cancer, that are now stable, are in remission, and do not require active therapy, are acceptable.
11. Patients requiring chronic anticoagulation are excluded from participation in the optional muscle biopsy collection.
