Background and Aims:

Reduced exercise and functional capacity are observed characteristics in patients with coronary artery disease. Diminished capacity may threaten the ability to meet even minimal activities of daily living (generally requiring a VO₂ capacity between 10 and 18 ml [middle dot] kg ^-1 [middle dot] min ^-1). The restoration and recovery of normal exercise and functional capacity is a goal of exercise-based cardiac rehabilitation. The ability to identify which exercise components(s) best predict incremental improvement to peak aerobic capacity (VO_2peak) within the exercise prescription may provide better direction to patients and improve exercise rehabilitation efficacy. The aim of this study was to determine which component(s) of exercise prescription would best predict peak aerobic capacity in patients with coronary artery disease following one year of exercise training.

Methods and Materials:

Hierarchical regression was performed on cross-sectional data from patients with coronary artery disease who were enrolled in the cardiac rehabilitation program of the Toronto Rehabilitation Institute between January of 1999 and June of 2004 (n = 3048; mean age = 61.3 +/- 10.1 SD; men = 2586; women = 462). Inclusion criteria were medical referral following recent bypass surgery, angina, myocardial infarction, angioplasty and/or insertion of a stent. Chronic heart failure patients were excluded. Following an initial cardiopulmonary assessment using a graded, cycle ergometer test, patients were prescribed walking exercise (50 to 85% heart rate reserve) in distance per day (DIS), duration (DUR) of exercise per day, and intensity as a minute/mile pace (INT). Patients exercised an average of 4 to 5 times per week for one year attending weekly, supervised classes. Variables used to predict post-training VO_2peak were age, sex, body mass index (BMI), percent body fat (%BF), initial VO_2peak at baseline, DIS, DUR and INT.

Results:

Age and gender accounted for 29.1% of the variance in VO_2peak (P < 0.001). BMI and body fat together explained an additional 8.4% variance, although only BMI contributed significantly (BMI: P < 0.001; %BF: P = 0.50). Initial VO_2peak added 30.1% of explained variance (P< 0.001). Controlling for all previously mentioned variables, exercise prescription in terms of DIS and DUR were the only significant predicting variables of VO_2peak (R² = 0.04; DIS: P< 0.001; DUR: P < 0.001; INT: P = 0.263). Overall, the best component of exercise prescription to predict peak aerobic capacity was DIS at the end of 12 months of supervised exercise ([beta] = 0.31). For every increase in mile walked per day would predict an increase in VO_2peak of 2.12 ml/kg/min. The final prediction model included gender, age, BMI, initial VO_2peak, DUR, and DIS which together significantly predicted VO_2peak (P < 0.001) explaining a total of 71.3% of the variance.

Conclusions:

Within aerobic exercise prescription, DIS and DUR were the best predictors of VO_2peak. Exercise prescriptions for patients with coronary artery disease may improve peak aerobic capacity without emphasis on intensity of walking. This regression model effectively quantifies a specific DIS of exercise required to find functional improvements.

Section Description

For more information, contact Marilyn Thomas (204) 488-5854