Background: A significant proportion of patients enrolled in cardiac rehabilitation programs are either overweight or obese. In a recent program evaluation of 259 patients, 39% listed weight loss and 23% listed increased cardiorespiratory fitness (CRF) as their primary goals for rehabilitation. Do the benefits of a cardiac rehabilitation program on changes in body mass and CRF depend on a patient's baseline level of obesity? The aim of this analysis was to determine the changes in body mass and CRF for a given level of baseline obesity in response to a 12-month cardiac rehabilitation program.

Methods: A retrospective study on 3,273 patients with coronary artery disease that completed a 12-month cardiac rehabilitation program at the Toronto Rehabilitation Institute from 1999 to 2005 was done. CRF was assessed using a symptom-limited graded exercise test with gas analysis to determine peak VO₂ at baseline, 6 months, and 12 months. Obesity was determined by body mass index (BMI, kg/m²) measured at baseline, 6 months, and 12 months. Data were grouped into the following BMI categories: <25 (n = 849), 25-29.9 (n = 1,655), 30-34.9 (n = 625), 35-39.9 (n = 113), >40 (n = 31) kg/m² for analysis.

Results: A total of 2,771 men and 502 women with an average age of 61.5 +/- 10.1 years, BMI of 27.6 +/-4.1 kg/m², waist circumference (WC) of 95.9 +/- 11.2 cm and VO₂ peak of 18.2 +/- 5.1 mL kg^-1 min^-1 completed the program. At baseline, 50.6 % of patients were overweight (BMI > 25), 23.5% obese (BMI > 30), and 30.9% abdominally obese (WC > 88 for women and >102 cm for men). The majority of subjects (58.1%) remained weight stable or gained body mass. Patients gained 0.8 +/- 3.3 (P = .0001), 0.3 +/- 4.0 (P < .0001), 0.3 +/- 5.1, and 0.3 +/- 6.0 kg in the <25, 25-29.9, 30-34.9, 35-39.9 BMI categories, respectively. Patients in the BMI > 40 category lost 3.9 +/- 8.8 kg (P = .02) which was significantly different from all other BMI categories. Patients below the WC threshold of obesity had a significant gain in body mass with no difference between groups. Patients gained CRF of 20.6 (P < .0001), 18.6 (P < .0001), 18.9 (P < .0001), 13.0 (P < .0001), and 8.5 (P < .01) percent in the <25, 25-29.9, 30-34.9 and > 40 BMI categories, respectively. Patients in the less than 25 BMI category had significantly greater gains in CRF than patients in the 35-39.9 (P = .01) and > 40 (P < .05) BMI categories. The abdominally obese (WC > 88 for women and >102 cm for men) had significantly smaller gains in CRF than patients below the WC threshold (P < .0001). There was a significant correlation between loss of body mass and gains in CRF (P < .0001).

Conclusions: There was a significant inverse relationship between obesity and gains in peak VO₂. Patients who enter cardiac rehabilitation as overweight or obese have an attenuated CRF response compared to those at a healthy BMI. Since a majority of people entering cardiac rehabilitation are overweight or obese, a focus on weight management strategies is clearly indicated.