| Plasma volume expansion is often observed in patients with myocardial infarction (MI) and is known to contribute to the progressive deterioration of cardiac function by exacerbating left ventricular (LV) dilation. Mounting evidence suggests that endurance exercise (End) training beneficially preserves cardiac function post-MI despite the concomitant changes to plasma volume and blood composition. In contrast, resistance exercise training (St) induces concentric cardiac hypertrophy, enhanced myocardial contractile force without causing plasma volume expansion. This may suggest resistance training be a promising therapeutic alternative in post-MI rehabilitation. The purpose of this study was to determine the ideal rehabilitative exercise intervention for the post-MI heart through the comparative analyses of the effects of endurance, and resistance exercise training on cardiac function, myocardial remodeling and hormonal responses in post-MI rats. MI was surgically induced in 7-wk-old rats by ligation of the left anterior descending coronary artery, with sham-operated animals serving as controls. The survivors were assigned to 4 groups: Sham (n=9,), MI-Sed (n=9, MI+no exercise), MI-End (n=7), and MI-St (n=10). One week after surgery, MI-End were trained on a rodent treadmill (at 16m/min, 50 incline, 40min/d, 5d/wk) and MI+ST were trained on a ladder with weight attached to tail (1 m high, step loading periodization, 3d/wk) for 10 wks. Our results showed that MI-St LV contraction velocities were greater than both MI-End and MI-Sed (P < .05). Circulating aldosterone and sodium concentrations were comparable among MI-End and MI-Sed, yet both were significantly (P < .05) greater than MI-St. Serum albumin concentration was elevated in MI-End compared to MI-St and MI-Sed (P < .05). Total blood volume and plasma volume were elevated in both MI-End and MI-Sed compared to MI-St (P < .05). The LV end-diastolic dimension (LVEDd) of MI-End and MI-Sed were similar, however both were greater than MI-St (P < .05). The LV end-systolic dimension (LVESd) of MI-St was notably lower than MI-End (P < .05), yet both MI-St and MI-End were less than MI-Sed (P < .05). The results of this study demonstrated post-MI resistance training preserved LV systolic function and reduced pathological dilation better than post-MI endurance exercise. The absence of sodium- and albumin-induced plasma volume expansion observed with post-MI resistance exercise may have contributed to the mitigation of hypervolemia, and the corresponding influences of volume overload conditions on systolic function. Therefore the data presented in this study suggests post-MI resistance training significantly attenuated LV dilation, with no observed adverse effects, and may be more beneficial to the preservation cardiac function in the post-MI heart. |
