The effect of interval training at modified speed on the development of some physical and physiological variables for the 1511m runners Dr. Mohamed Al-Hussein Al-Metwally Abstract: This research aims to identify the effectiveness of interval training on the development of physiological variables for 1511m runners represented in (anaerobic capacity - relative and absolute VO2MAX maximum oxygen consumption - LACTATE THRESHOLD rate before and after the effort - speed associated with maximum oxygen consumption vVO2MAX - running economy). EXERCISE RUNNING ECONOMY Ventilation Equivalent (VE-Ed) Vital capacity EPOC- Heart rate before and after the effort. Procedures The study sample consisted of 8 runners in the 1511m race at Kafr Saqr Club and registered in the Egyptian Athletics Federation (weight 66.42 ± 1.11, kg, height 171.1 ± 1.82, cm, age 17). 83 ± 1.56, years, training age 4.61) The researcher applied the program to the sample under study, and the physical variables were measured in the stadium and the physiological variables were measured in the laboratory of the means of Measurement.The most important results There are statistically significant differences at the level of Sig.(p.value) < 1.15 between the tribal and remote measurements in the physical and physiological variables in favor of the post measurement in the physical variables and anaerobic and physiological capacity, which ranged between (2.15:: 39.19:) for the structural variables between the measurement of speed endurance Run 611 meters and endurance both legs, while the percentage of improvement in the anaerobic variables ranged between (4.57:: 9.34:) for the maximal anaerobic capacity and the fatigue index, while the percentages of improvement in the physiological variables ranged between heart rate at rest and the maximum relative oxygen consumption (1.16 % 11.83) Recommendations- To be guided by the tests used in the research when evaluating the variables of aerobic endurance and anaerobic capacity and to benefit from the methods of rationing the loads used in this training program when designing training programs in different races commensurate with the type of exercises and different age stages . - Using interval training at a modified speed in various sports activities and for different age groups during different season periods to identify the functional and biochemical responses to aerobic training Keywords: Interval training at average speed