Did you know a study was performed by the Exercise Physiology Laboratory at California State University to investigate the difference in muscle activation between the smith machine bench press and the barbell bench press. Researchers used electromyography to compare muscle activation levels for the medial deltoid, the anterior deltoid, and the pectoralis major. 14 experienced and 12 inexperienced subjects volunteered for the study, and were categorized according to prior bench press experience to explore whether it had an effect.
Testing took place on two different days one week apart from each other; one day consisted of free weight bench press and the other the smith machine. The one rep maximum (1RM) was determined for each participant in conjunction with the exercise being performed that day. The test consisted of two repetitions at 70% of their 1RM and two repetitions at 90% of their 1RM.
To control variables in exercise form for each exercise the participants were told when to lift the bar off the rack, which they then held at full elbow extension until instructed to lower the bar in a controlled manner. Once the bar touched their chest, to control for bouncing, the participants didn’t start the concentric part of the lift until the tester gave a verbal cue to “push”. Each subject also used a standardized grip width of 165% of their biacromial breadth (shoulder width).
To the surprise of many of you reading this researchers found no difference in muscle activation of the pectoralis major and the anterior deltoid regardless of exercise, load, or experience level. Conversely, the medial deltoid was significantly more active during the free weight bench despite load differences and experience.
The difference in medial deltoid activation is related to the inherent instability of the free weight bench compared to the smith machine, which illuminates the role of the medial deltoid as a glenohumeral stabilizer.
Journal of Strength and Conditioning Research, 24(3), 779-784. (2010). Retrieved from http://bit.ly/1Jtzp6B
Because of the more natural, sport-specific stabilizing effect of the free weight bench, athletes wanting to improve performance would be better off utilizing the free weight bench over the smith machine bench. However, if hypertrophy and strength of the pectoralis major and anterior deltoid are your goals, as in physique competition, either exercise will equally suit your needs. The medial head of the deltoid can be worked thoroughly with other exercises.