Physical inactivity is a risk factor for repeat cardiac events and all-cause mortality in coronary heart disease (CHD). Cardiac rehabilitation, a secondary prevention programme, aims to increase physical activity levels in this population from a reported low baseline. This trial will investigate the effectiveness and implementation of a very brief physical activity intervention, comparing different frequencies of physical activity measurement by cardiac rehabilitation clinicians. The Measure It! intervention (

This type 1 hybrid effectiveness–implementation study will use a two-arm multicentre assessor-blind randomised trial design. Insufficiently active (

The study has ethical approval (University of Canberra (ID 11836), Calvary Bruce Public Hospital (ID 14-2022) and the Greater Western Area (ID 2022/ETH01381) Human Research Ethics Committees). Results will be disseminated in multiple formats for consumer, public and clinical audiences.

ACTRN12622001187730p.