Abstract
The aim of the study is to determine how circuit training affects the fitness of volleyball players. This research employs an experimental approach using a “one-group pretest-posttest design”. The research instrument is the TKJI (Indonesian Physical Freshness Test) tailored for the age group of 16-19 years. The study population comprises volleyball players from the IPK Kuamang club, with a total of 20 individuals. Sampling was conducted using a targeted sampling technique, and the sample consisted of 10 individuals. Data analysis was carried out using the Liliefors normality test and t-test with a significance level of α = 0.05. The results indicated a significant effect of circuit training on physical fitness, as evidenced by an average pre-test score of 12.3 and an average post-test score of 15.2. This conclusion is supported by the finding that t_count = 13.1 > t_table = 1.833 after completing the t-test. Therefore, H₀ is rejected, and H₁ is accepted. Hence, circuit training significantly impacts physical fitness.

Keywords
circuit training, physical fitness, volleyball