Most research involving rodents has analyzed biomechanical gait parameters under pathological conditions, with some studies exploring the effects of moderate-intensity training on these variables in the context of aging and disease. Additionally, aging and obesity in humans cause morphological changes in the musculoskeletal system, while physical exercise helps mitigate muscle deterioration. This study aimed to investigate linear gait kinematics and muscle tissue morphometry in Wistar rats of different ages, fed a high-fat diet (HFD), and subjected to a HIIT protocol. Thus, the aim of this study was to analyze linear kinematic gait parameters, as well as morphometric aspects of muscle tissue in Wistar rats of different ages fed with an HFD diet and subjected to a high-intensity interval training (HIIT) protocol. Seven-, nine-, 12- and 18-month-old male Wistar rats divided in 16 groups (n = 7):​ T-SD and S-SD (trained and sedentary fed with standard diet), S-HFD and T-HFD (trained and sedentary fed with high-fat diet) were subjected to a HIIT protocol, 3x a week, for 8 weeks. After the training period, the gait cycles of all groups were recorded. The cross-sectional area of the muscle fibers of the soleus and extensor digitorum longus was assessed. The practice of HIIT body mass and causing muscle fiber hypertrophy regardless of diet and age (p < 0.001), increased maximum running capacity, reduced stride length, stride and support time, and increased stride frequency, even under the influence of age (p < 0.001). As a conclusion, HIIT promoted greater linear locomotor efficiency, resulting in a more efficient and dynamic gait. Obesity condition did not directly affect the linear variables analyzed.