Studies investigating multi joint exercises (such as the bench press) and single joint exercises (such as the dumbbell fly, pec deck machine, and bent - forward cable cross-over) have generally found similar levels of pectoralis major EMG amplitude across all exercises, which suggests that either type of exercise can be used to good effect (Welsch et al. 2005; Rocha - Junior 2007; Shanke 2012). (strengthandconditioningresearch.com)
Overall, research indicates that the free - weight and machine bench press produce very similar levels of pectoralis major EMG amplitude and therefore either will train the muscle effectively. (strengthandconditioningresearch.com)
The pec major is the largest and most superficial of the anterior axioappendicular muscles, lying superficial to the entire pectoralis minor and subclavius, and part of the serratus anterior. (kingofthegym.com)