The effects of strength vs. endurance exercise training on cardiac function and remodeling in post-myocardial infarction rats

Increased plasma volume (PV) is consistently observed in patients with myocardial infarction (MI), and contributes to the progressive decline in cardiac function by exacerbating left ventricular (LV) dilation; however, compelling evidence suggests that endurance exercise training, despite eliciting a marked increase in PV, beneficially preserves post-MI cardiac function. Contrarily, strength exercise training, which promotes concentric myocardial hypertrophy and has no effect on PV, may be more therapeutic in post-MI applications; therefore, the purpose of this study was to investigate for the first time the effects of strength vs. endurance exercise training on myocardial function and remodeling in post-MI rats. MI was surgically induced on 7-wk-old Sprague-Dawley rats by ligation of the coronary artery. The survivors were assigned to 4 groups (n=10/group): Sham (no MI, no exercise), MI-Sed (MI, no exercise), MI-End (MI+endurance exercise), and MI-St (MI+strength exercise). Endurance and strength exercise training using a rodent treadmill or an 85¢ª inclined ladder, respectively, began 1-wk post-MI and lasted for 10-wks. Echocardiogram measurements (Echo) were performed on the day prior to initiation of exercise training and at the end of exercise training, while in vivo pressure-volume analysis (PVAN) were conducted at the end of exercise training. Echo data revealed that although fractional shortening (FS%) was well preserved in both exercise trained groups compared to the MI-Sed group, LV end-diastolic dimension was significantly lower in the MI-St group compared to the MI-End group (1.075¡¾0.01 vs. 1.184¡¾0.02 cm, p<0.05); furthermore, PVAN data illustrated that dP/dt max values were significantly higher in the MI-St than in the MI-End group (7124.4¡¾293.9 vs. 5888.0¡¾176.8 mmHg/s, p<0.05). Lastly, post-MI strength training significantly elicited a concentric hypertrophic response in the LV posterior wall (p<0.05). Together, these results suggest that strength training may be more beneficial than endurance training at preserving post-MI cardiac function; in addition, this study demonstrated that post-MI strength training significantly attenuates LV dilation without causing any observable adverse effects.