Despite a paucity of evidence, patients following cardiac surgery via median sternotomy are routinely prescribed sternal precautions that restrict upper limb and trunk movements, with the rationale of reducing postoperative sternal complications such as sternal wound dehiscence, instability, infection and/or pain. The primary aim of this study was to measure motion at the sternal edges during dynamic upper limb and trunk tasks to better inform future sternal precautions and optimise postoperative recovery. Motion at the sternal edges was measured using ultrasound, which has been demonstrated to be a clinically valid and reliable measure in patients following cardiac surgery.Seventy-five patients following cardiac surgery via median sternotomy with conventional stainless steel wire closure were recruited. Motion at the sternal edges in the lateral (coronal plane) and anterior-posterior (sagittal plane) directions was measured at the level of the fourth intercostal space (mid-sternum) using ultrasound. Ultrasound measures were taken at rest and during five dynamic upper limb and trunk tasks (deep inspiration, cough, unilateral and bilateral upper limb elevation and sit to stand), over the first 3 postoperative months (3 to 7 days, 6 weeks and 3 months postoperatively). Sternal pain, functional status and sternal healing were also observed over the same postoperative period.The magnitude of overlap of the sternal edges in the lateral direction, and separation of the sternal edges in the anterior-posterior direction, both significantly decreased by 0.01cm, over the first 3 postoperative months (p<0.01). Coughing, however, produced a significant increase in separation of the sternal edges in the lateral direction (0.01-0.02cm) and pain (12-63%), compared to rest and all other tasks, at each postoperative time point (p<0.01). Additionally, there was a significant decrease in sternal pain (81%) and increase in postoperative function (79%) over the same postoperative period (p<0.01). At 3 months postoperatively, five (7%) participants demonstrated radiological sternal union and one (1%) participant was diagnosed with clinical sternal instability.A small magnitude of multi-planar motion at the sternal edges, at the mid-sternum, was demonstrated during dynamic upper limb and trunk tasks in a cohort of cardiac surgery patients post-sternotomy, over the first 3 postoperative months. Future research investigating motion at different levels of the sternum, with varying methods of sternal closure, and over a longer postoperative period is warranted to better inform sternal precautions and optimise postoperative recovery.