The aim of the research is to study the effect of interval training with a modified speed on the development of some physical and physiological variables for the 1500-meter runners. The research sample was chosen by the intentional method from the 1500-meter juniors registered in the Sharkia region and registered with the Egyptian Athletics Federation for the 2019/2020 season, and they are training in the Kafr Saqr Sports Club. The total number of the research sample was (13) contestants, and the two researchers randomly selected (5) contestants for the study The survey was drawn from the research community and outside the basic research sample, thus the basic research sample consisted of (8) contestants. The researchers used physical and physiological measurements as a means of collecting data, and the most important results were the effect of the training program using the modified speed interval training on the development of some physical and physiological variables for the 1500m contestants, and the most important recommendations were the use of the modified speed interval training in developing some physical and physiological variables for athletes in various sports activities and age stages Different phases during the different seasons to identify the functional and biochemical responses to aerobic training.