Study design, randomisation and blinding
IMPACT-Women is a two-site, two-arm, parallel-group superiority randomised controlled trial. Participants will be randomised 1:1 to the two groups using permutated blocks with random block sizes of two and four, stratified by study site, chemotherapy type (adjuvant/neoadjuvant), and postmenopausal status (yes/no). Randomisation will occur after completion of baseline assessments using a blinded online electronic randomisation tool, with enrolment and assignment performed by a research coordinator. All outcome assessors will be blinded to group assignment. Blinding participants to a behavioural intervention is not possible but is not expected to bias our physiological outcomes. Participants’ treating oncologists will not be blinded as we expect that group assignment may need to be discussed during care.