The essence of training theory is that a structured training system can be formed, consisting of training activities that target the physiological, psychological, and performance characteristics associated with individual sports. Core training models are needed for adolescent athletes because core muscles are the foundation of the human body. with the needs of adolescent athletes. This study aims to test the practical construction of the exercise model so that it can find out the results of the feasibility test from experts and the effectiveness of the core stability training model using the Swiss ball for student athletes aged 15-17 years, this study uses the research & development(R&D) method applying borg and gall , with a quasi-experimental research design in the form of a pretest-posttest control group design. The research subjects were 60 student athletes aged 15-17 years.Comparison of the results of the effectiveness test through the core test before 1.86 and after being given treatment 2.76. it means that the average score of the core test of student athletes aged 15-17 years who are the subjects there is an increase, from the results obtained it can be concluded that: (1)The core stability training model using a swiss ball for student athletes aged 15-17 years in the form of 20 training models has gone through the training phases so that it is feasible to use, in addition to support in the form of books and applications accompanied by pictures and explanations of core exercises that include, the purpose of the procedure, the training program and the equipment needed to be systematically used as a reference for core training, (2) the model that is applied is safe and effective to increase the strength or endurance of the core muscles for student athletes aged 15-17 years. The effectiveness indicator is determined by calculating the N-gain with the category of "high enough" or the category of effectiveness interpretation in the form of "effective", so that the core stability exercise model using the swiss ball is declared safe by experts and suitable for use for student athletes aged 15-17 years.
Key Words: Core, Core Stability, Swiss Ball, Strength,