Background and Aims: Prognosis for persons who have experienced a cardiac event is worsened with the presentation of comorbidities. Diabetes mellitus (DM) increases relative risk of mortality or serious morbidity 1.5- to 3-fold in individuals who have had a previous coronary event. Although the physiological consequences of an added comorbidity are distinct, exercise is similarly prescribed for disease management in both populations to improve fitness and risk factors. However, if improvements in fitness in a person with coronary artery disease (CAD) differ from those with both CAD and DM, the adoption of population-specific exercise guidelines may improve exercise rehabilitation efficacy. The aim of this study was to determine if the presence of DM in persons with CAD diminished improvements in peak aerobic capacity following 1 year of exercise training.

Methods and Materials: Hierarchical regression was performed on cross-sectional data from patients with CAD who were enrolled in the cardiac rehabilitation program of the Toronto Rehabilitation Institute between March of 1999 and December of 2004 (n = 1,303; mean age = 60.1 years +/- 0.3 SE; men = 1,105; women = 198). From this cohort, 212 participants also had DM as a concomitant diagnosis to CAD. Inclusion criteria were medical referral following recent bypass surgery, angina, myocardial infarction, angioplasty and/or insertion of a stent, and use of oral hypoglycaemic agents, insulin, or prior medical diagnosis of DM for inclusion in the CAD + DM group. Following an initial cardiopulmonary assessment using a graded, cycle ergometer test, walking exercise was prescribed at 60% to 75% heart rate or VO₂ reserve as tolerated in distance and duration. Patients exercised an average of 4 to 5 times per week for 1 year attending weekly, supervised classes. Differences in posttraining peak aerobic capacity (VO_2peak) between CAD and CAD + DM participants were determined after controlling for age, sex, body mass index (BMI), initial VO_2peak at baseline, and amount of self-reported exercise performed.

Results: After 1 year of exercise training, participants with CAD alone and those with CAD+DM walked similar distances per day (average: 3.12 +/- 0.04 miles) and frequency (4.7 +/- 0.1 times) per week. Duration of exercise per day was significantly different between persons with CAD and those with CAD+DM (50.0 +/- 0.4 minutes vs 47.9 +/- 1.0 minutes, respectively; P < .05). Our regression model predicting VO_2peak had significant predictors of age and gender (explaining 28% of the total variance, P < .001), BMI (R² = 0.08, P < .001), initial VO_2peak (R² = 0.35, P < .001), as well as exercise prescription (R² = 0.02 [distance and duration, not frequency], P < .001). Controlling for all previously mentioned variables, the presence of diabetes as a comorbidity was found to be a significant predictor of peak aerobic capacity (R² = 0.01, P < .001). The presence of DM with CAD predicts a smaller improvement in VO_2peak by 1.6 mL kg^-1 min^-1 compared to the average person with CAD alone following 1 year of exercise rehabilitation.

Conclusions: Exercise rehabilitation for persons with CAD and DM may require an altered exercise training approach than that of CAD patients to maintain similar exercise benefit. Future research into the optimal aerobic and resistance exercise prescription for persons with CAD and DM is needed to elucidate this program.