This class action research was carried out with the aim to improve the physical fitness of class X students of SMKN 1 Sakra in the 2018/2019 Academic Year. The method used in this research is to use class action research. The research subjects used in this study were all students of class X SMKN 1 Sakra, East Lombok Regency in the 2018/2019 Academic Year. This research was conducted in odd semester. The results showed that 32 children who have been given action in cycle I, cycle II and cycle III produce the following conclusions: 1) Physical fitness through modification of the running game makes the learning atmosphere more active, students are better able to display their respective characters while moving their feelings confidence, cooperation, courage and good sportsmanship. 2) The application of running game modifications can improve physical fitness, this can be proven by the results of the analysis of cycle I to cycle II and cycle II to cycle III, 3) The application of running game modifications can im   rove physical fitness learning outcomes, with the percentage of class completeness reaching 78.12 %.