Exercise Volume Modulates Cardiac Protection in a Type 2 Diabetic Rat Model: Differential Effects of High- and Low-Volume Moderate-Intensity Endurance Exercise Training on Diabetic Cardiomyopathy

Background Cardiomyopathy is a major complication of type 2 diabetes, whose prevalence continues to rise globally. Although major cardiology and endocrinology societies endorse exercise training to reduce cardiovascular risk, the optimal exercise training modality, and specifically the role of exercise volume, in preventing diabetic cardiomyopathy remains unclear. Methods Male Sprague Dawley rats were fed a high-sugar diet to induce type 2 diabetes. At diet onset, animals were assigned to high-volume (HVE, N = 7) or low-volume (LVE, N = 8) moderate-intensity treadmill training, performed five days per week for 18 weeks. Sedentary rats served as controls (N = 6). Cardiac function was assessed using conventional echocardiography, strain imaging, and invasive hemodynamics. Plasma analyses were used to identify systemic metabolic status, and ex vivo techniques quantified left ventricular cardiac fibrosis, oxidative stress, hypertrophy, inflammation, and metabolism. Results After 18 weeks of diet, sedentary rats developed characteristic features of early-stage diabetic cardiomyopathy, accompanied by impaired systolic function and increased interstitial myocardial fibrosis. Conversely, high volumes of moderate-intensity exercise training partially prevented pathological cardiac remodelling by improving cardiac metabolic regulation, reducing oxidative stress, and enhancing both cardiac stress-responses and systemic metabolic control. Lower volumes of exercise training primarily reduced oxidative stress and inflammation, resulting in only modest cardioprotective effects and limited preservation of cardiac function. By contrast, high-volume exercise training elicited more pronounced cardioprotective effects, reflected by a significantly higher ejection fraction (p < 0.006), cardiac output (p < 0.002), and stroke volume index (p < 0.006) relative to sedentary controls. Conclusion The progression of diabetic cardiomyopathy is strongly modulated by the volume of exercise. High-volume moderate-intensity exercise training confers superior cardioprotection compared with low-volume training, underscoring the importance of incorporating sufficient exercise volume into evidence-based exercise prescriptions for individuals with type 2 diabetes.