Relationship between exercise tolerance and muscle strength following cardiac rehabilitation: Comparison of patients after cardiac surgery and patients with myocardial infarction

Background and purpose Previous studies have demonstrated that cardiac rehabilitation (CR) improves exercise tolerance and muscle strength in patients with myocardial infarction (MI) and in patients after cardiac surgery. However, the association between exercise tolerance and muscular strength following CR and the comparison of relationships among various disease categories has not been fully examined. The purpose of the present study was to assess the relationship between exercise tolerance and muscle strength following CR in patients after cardiac surgery and patients with MI. Methods and results One hundred and four patients who participated in CR for 6 months were enrolled [post-cardiac valve surgery (VALVE), n = 28; post-coronary artery bypass grafting (CABG), n = 42; post-acute MI, n = 34]. The exercise tolerance, thigh/calf circumferences, and muscle strength were measured before and after CR. At the baseline, the thigh circumference was significantly smaller in the VALVE group than in the MI group. There were significant positive correlations between peak V˙⁡O2 and muscle torques of the lower muscles in all groups. After 6 months, peak V˙⁡O2 and muscle torque were significantly increased in all groups (p < 0.001). A positive significant correlation between percent increases in peak V˙⁡O2 and muscular strength was observed in the VALVE group (r = 0.51, p < 0.01), but not in the other groups. In addition, the changes in peak V˙⁡O2 and calf circumference after CR were significantly higher in the VALVE group than in the MI group. Conclusions These data suggest that exercise intolerance in patients after heart valve surgery may in part depend on decreased muscular strength. Further studies are needed to assess whether the strategy of increasing muscular strength of lower limb by programmed resistance training could be effective for improving exercise intolerance in patients after heart valve surgery and symptomatic patients with heart failure.