Prolonged sedentary time is recognized as a distinct health risk, and mortality risks are expected to be greatest for individuals with low exercise levels. It is unknown whether participation in exercise-based cardiac rehabilitation (CR) programs influences sedentary behaviour particularly among those patients expected to be at greatest mortality risk. This study examined the influence of CR participation on sedentary behaviour and identified the proportion and characteristics (socio-demographic and clinical) of patients who do not meet exercise recommendations and have prolonged sedentary times.

A prospective study was conducted among patients of an exercise-based CR program and assessments performed at baseline and 3 months. Physical activity and sedentary behaviour information were collected by self-report, and convergent validity was examined on an accelerometer-wearing subsample.

Of 468 CR patients approached, 130 participants were recruited with an average sedentary time of 8hours/day. Sedentary behaviour remained consistent at follow-up (relative change= −2.4%, P=0.07) notwithstanding a greater proportion meeting exercise recommendations (relative change= 57.4%). 19.2% of participants were classified to have prolonged sedentary time and not meet exercise recommendations at baseline. No significant differences were found between the characteristics of high-risk individuals and lower risk subgroups. Findings were consistent among the accelerometer-derived subgroup and the overall sample despite poor to moderate convergent validity.

These results suggest that the exercise-focus of CR may not reduce sedentary behaviours. Future studies are needed to determine whether sedentary behaviour-specific reduction strategies are more effective than traditional exercise-based strategies and lead to meaningful improvements in clinical outcomes.