OBJECTIVE It has been well known that the stress of heavy-resistance exercise has a potent effect for both strength development and muscle fiber hypertrophy. This may be due, at least in part, to exercise induced acute increase in se- rum anabolic hormone. Therefore, the purpose of this study was to compare the effects of three different rest intervals on IGF-1, cortisol (CO), Creatine Kinase (CK), and blood lactate concentrations. METHODS Hence, ten recreationally strength-trained men (age=20.37 ± 2.44 years, body mass= 65.6 ± 26.70 kg) volunteered as subjects that in 4 separate sessions with 48 h from each other performed 4 different resistance trainings (RT). In the first session, one repetition maximum (1RM) was determined. From second to forth session, subjects performed 4 sets of squat and bench press with 85% of 1RM until exhausted and one of the rest intervals (60, 90 and/or 120 second) was used in a random order between sets. RESULTS It wasn’t observed a significant difference among the three programs in IGF-1 concentration. However, it was observed a significant increment of 3.6 and 23 percent in IGF-1 concentration immediately and 30 min after exercise during RT with 60 s rest between sets. CO concentration in protocols with 60 and 90 s rest increased significantly more than 120 s protocol. CK and blood lactate concentration changes weren’t differing between protocols but post exercise CK concentration significantly increased in each protocol. DISCUSSION & CONCLUSION Growth factors, including IGF-I are known to be mediators of satellite cell activation, increased protein synthesis, decreased protein degradation, hyperplasia, and myofibril hypertrophy during muscle growth and development (Jennische, 1987). The response of IGF-I to acute RT is less clear. In the present study, although postexercise values of IGF-1 during three protocols increased but IGF-1 concentration changes immediately after protocols were significant only in RT program with 60 s rest b
