When is the best time to exercise during breast cancer treatment?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Aged 21-80 years * Female * MSK histologically confirmed early-stage operable breast cancer * Scheduled to receive chemotherapy in the neoadjuvant or adjuvant setting * ECOG status of 0 or 1 * Performing less than 150 minutes of structured moderate-intensity or strenuous intensity exercise per week * If a female of child-bearing potential, must not be pregnant or planning to become pregnant during the study. a. Women \< 50 years old must have a negative pregnancy test (urine HCG or serum βHCG) within 2 weeks of beginning chemotherapy. * Able to complete an acceptable baseline cardiopulmonary exercise test (CPET), in the absence of high risk ECG findings or other inappropriate response to exercise as determined by the investigator. * Able to achieve an acceptable peak baseline CPET, as defined by any of the following criteria: * Achieving a plateau in oxygen consumption, concurrent with an increase in power output; * A respiratory exchange ratio ≥ 1.10; * Attainment of maximal predicted heart rate (HRmax) (i.e., within 10 bpm of age-predicted HRmax \[HRmax = 220-Age\[years\]); * Volitional exhaustion, as measured by a rating of perceived exertion (RPE) ≥ 18 on the BORG scale. * Willingness to be randomized to one of the study arms Exclusion Criteria: * Presence of any other concurrent, actively treated malignancy * History of any other malignancy treated within the past 3 years (other than non-melanoma skin cancer) * Presence of metastatic disease * Any of the following contraindications to cardiopulmonary exercise testing: * Acute myocardial infarction within 3-5 days of any planned study procedures) * Unstable angina * Uncontrolled arrhythmia causing symptoms or hemodynamic compromise; * Recurrent syncope * Active endocarditis * Acute myocarditis or pericarditis * Symptomatic severe aortic stenosis * Uncontrolled heart failure * Acute pulmonary embolus or pulmonary infarction within 3 months of any planned study procedures; * Thrombosis of lower extremities * Suspected dissecting aneurysm * Uncontrolled asthma * Pulmonary edema * Respiratory failure * Acute non-cardiopulmonary disorders that may affect exercise performance or be aggravated by exercise (i.e., infection, renal failure, thyrotoxicosis) or * Room air desaturation at rest ≤ 85% * Mental impairment leading to inability to cooperate. * Any other condition or intercurrent illness that, in the opinion of the investigator, makes the participant a poor candidate for the trial