Adult hippocampal neurogenesis (AHN) is the process of generating new neurons in the adult hippocampal dentate gyrus (DG). Exercise promotes AHN and improves hippocampal function through neuroplastic enhancement. The underlying regulatory factors of this process are currently being vigorously studied. However, many previous studies have used a rodent wheel-running model, in which the exercise condition (e.g., volume, intensity, duration) cannot be controlled. In contrast, treadmill running (TR) allows the precise regulation of conditions such that animals can run according to specific experimental aims. Understanding the intensity-dependent effects of exercise on AHN and hippocampal functions, and the underlying mechanisms, is crucial for the development of exercise prescriptions for humans in diverse educational and clinical fields. Based on the lactate threshold (LT), an inflection point at which blood lactate accumulation drastically rises during incremental exercise, exercise can be defined as minimal-stress light-intensity exercise (below LT) and exercise-derived-stress vigorous-intensity exercise (above LT). This chapter begins with a brief overview of AHN, followed by a discussion of LT-based exercise effects on AHN and hippocampal function as they vary with exercise intensity, primarily following the findings from the TR models, and closing with the molecular factors involved in AHN and hippocampal function regulation.