Most studies on rodent gait biomechanics focus on pathological conditions, but recent research has begun to explore moderate training. Aging and obesity lead to morphological and functional changes in skeletal muscle, especially in ECM and collagen fibers. Given the growing use of animal models, understanding how morphological and functional changes in skeletal muscle impact the three-dimensional angular kinematics of rat hindlimb gait in relation to the extracellular matrix (ECM) is essential. For this purpose, this study aimed to evaluate the three-dimensional angular kinematics of the knee and ankle during gait in rats of different ages, subjected to a high-fat diet (HFD) and HIIT, linking these aspects to muscle ECM characteristics. Male Wistar rats, aged seven, nine, 12, and 18 months, were divided into 16 groups (n = 7):​ T-SD and S-SD (trained and sedentary on standard diet), S-HFD and T-HFD (sedentary and trained on HFD). Trained rats underwent an 8-week HIIT protocol, 3x a week. Gait cycles were recorded, and ECM area and types I and III collagen in the soleus and EDL muscles were measured. HIIT reduced the maximum knee peak in T-SD groups (p = 0.0002), while HFD decreased this in S-HFD groups (p = 0.0012). HIIT also lowered the ankle peak in T-SD and T-HFD groups (p < 0.0001). Muscle ECM remodeling and type I collagen were related to age (p < 0.0001), while HIIT influenced type III collagen remodeling (p < 0.0001). These findings advance understanding of motor behavior and ECM remodeling in obese and aged rodents, guiding age standardization in exercise studies.