OBJECTIVES: To develop a reference chart to monitor inspiratory muscle strength during pre-operative inspiratory muscle training for patients at high risk of developing postoperative pulmonary complications awaiting coronary artery bypass graft (CABG) surgery. DESIGN: Secondary data analysis using patients from the intervention arm of a randomised clinical trial. SETTING: University medical centre. PARTICIPANTS: Patients at high risk of developing postoperative pulmonary complications awaiting CABG surgery. INTERVENTIONS: Patients performed inspiratory muscle training seven times per week for at least 2 weeks before surgery. MAIN OUTCOME MEASURES: Maximal inspiratory muscle strength. RESULTS: A new reference chart was produced using a non-linear time trend model with a normal error structure. CONCLUSIONS: The chart is a novel tool for monitoring the progress of inspiratory muscle training for physiotherapy practice. Wider use of this chart is recommended.