Purpose. To evaluate the changes in circumference sizes of bodybuilders using machine and free weight exercises in conditions of different load regimes at the stage of specialized basic training. Methods. 64 bodybuilders aged 20±1.2 years were divided into 4 study groups. The stage of specialized basic training lasted 12 weeks. Group 1 and 2 participants used free weight and machine exercises in conditions of medium-intensity training load (R_а=0.58). Group 3 and 4 athletes performed the same exercises in conditions of high-intensity training load (R_a=0.71). The changes in circumference measurements (shoulder, hip and shin) were recorded every 30 days. Non-parametric methods of mathematical statistics were used in the study. The results. Using free weight exercises in the regime of high-intensity loads (R_а=0.71) contributed to the greatest increase in the body circumference (by 4.9%) compared to the initial data. The smallest increase in the controlled indicators (by 1.8%) was found in athletes using machine exercises in the regime of medium-intensity loads (R_a=0.58). Performing free weight exercises in different load regimes led to more than double increase in the body circumference measurements. The dependence of the controlled indicators dynamics on the load regimes was observed when using machine exercises. The dynamics of body circumference depends on the features of the training load regimes but not on the type of exercises. Conclusions. At the stage of specialized basic training in bodybuilding, the use of high-intensity training loads (R_a=0.71) was the main factor that affected the accelerated increase in body circumference of athletes. Combination of machine strength exercises with high-intensity loads allowed achieving the most pronounced adaptive changes.