The aim of this study was to compare the effects of substitution of upper and lower body exercises during rest intervals on the quantity of upper body performance and lactate with 75% 1RM (Repetition maximum). For this purpose, 15 trained bodybuilders (age 20.9±1.9 years, weight 74.8±5.2 kg and aerobic power 35.48±8.6 ml/kg/min) took part in this study voluntarily. All subjects performed four testing sessions of bench press with 48 hours of recovery between sessions. In the first session, 1RM was measured. During the second to fourth session, subjects performed four sets per session with 75% 1RM up to voluntary exhaustion. In each session, subjects completed one of the following models: bench press movement with inactive rest (P1), bench press movement with leg extension and inactive rest (p2), and bench press movement with seated rowing and inactive rest (p3) randomly. For statistical analysis of data, two-way repeated measures ANOVA and LSD post hoc test were used. The results showed that all three exercise models reduced the repetitions in consecutive sets, and there were significant differences between consecutive sets (P=0.001). Also, sustainability of repetitions in P1 exercise model was significantly higher than P3 exercise model (P=0.001), and P2 exercise model than P3 exercise model (P=0.02). The present findings indicated a significant difference between lactate produced during P1 and P3 models (P=0.001), and P2 and P3 models (P=0.03). Therefore, as there was no significant difference between percentage of repetition and lactate production during exercise models of P1 and P2, it seems that combined upper and lower exercise reduces the time of exercises and maintains the repetitions at a higher level through decreasing lactate accumulation.