This research aims to study the effect of high-intensity interval training with short and long duration repetitions on the development of some physical and physiological variables in junior squash players under 15 years of age. The researcher used an experimental design with two experimental groups, employing pre- and post-tests for both groups. The research sample was selected purposively and included (12) junior squash players under 15 years of age from Al-Zohour Sports Club, registered with the Egyptian Squash Federation for the 2023-2024 academic year. The training program lasted for 8 weeks, with 3 training sessions per week. The most important finding of the research was the absence of statistically significant differences between the two experimental groups. The first group (high-intensity interval training) The second (high-intensity interval training with long-duration repetitions) in the post-test measurement of some physical and physiological variables (maximum oxygen consumption, maximum aerobic speed, time to exhaustion, anaerobic capacities) for junior squash players.