J Strength Cond Res. 2010 Jan 21. [Epub ahead of print]
A Comparison of Muscle Activation Between a Smith Machine and Free Weight Bench Press.
Schick EE, Coburn JW, Brown LE, Judelson DA, Khamoui AV, Tran TT, Uribe BP.
Exercise Physiology Laboratory, Department of Kinesiology, California State University, Fullerton, California.
Schick, EE, Coburn, JW, Brown, LE, Judelson, DA, Khamoui, AV, Tran, TT, and Uribe, BP. A comparison of muscle activation between a Smith machine and free weight bench press. J Strength Cond Res 24(X): 000-000, 2010-The bench press exercise exists in multiple forms including the machine and free weight bench press. It is not clear though how each mode differs in its effect on muscle activation. The purpose of this study was to compare muscle activation of the anterior deltoid, medial deltoid, and pectoralis major during a Smith machine and free weight bench press at lower (70% 1 repetition maximum [1RM]) and higher (90% 1RM) intensities. Normalized electromyography amplitude values were used during the concentric phase of the bench press to compare muscle activity between a free weight and Smith machine bench press. Participants were classified as either experienced or inexperienced bench pressers. Two testing sessions were used, each of which entailed either all free weight or all Smith machine testing. In each testing session, each participant's 1RM was established followed by 2 repetitions at 70% of 1RM and 2 repetitions at 90% of 1RM. Results indicated greater activation of the medial deltoid on the free weight bench press than on the Smith machine bench press. Also, there was greater muscle activation at the 90% 1RM load than at the 70% 1RM load. The results of this study suggest that strength coaches should consider choosing the free weight bench press over the Smith machine bench press because of its potential for greater upper-body muscular development.
Study findings:
(1) Greater muscle activation occurs at 90% max vs. 70% regardless of experience level or exercise (smith vs. free weight)
(2) There is no difference in muscle activation of the pectoralis major and anterior deltiod between exercises
(3) The free weight bench press results in greater activation of the middle deltoid
The authors commented: "The instability caused by the free weight bench press necessitates a greater response by the medial deltoid [sic] as both a force producer and perhaps more importantly as a stabilizer."
Gymnastics implications: In the past individuals have argued that greater stability (such as with a smith machine) will result in greater activation of the prime movers since the neural drive will not be "used up" by activating stabilizer muscles (as shown by greater loads that can be lifted). However, this study showed that greater instability does not inhibit activation of the prime movers. It is therefore plausible that the pecs and anterior delt are not inhibited during planche or ring pushups. As this study shows, greater activation of shoulder stabilizers probably occur in such pushups. The authors commented that improved shoulder stability properties of the free weight bench press make it a better candidate for sports.
As a comparison to this study, data published in Stuart McGill's, "Ultimate Back Fitness and Performance," looked at EMG amplitudes as a % of maximal voluntary contraction for various pushup exercises. The standard pushups (more stability) did not show greater activation of the pecs, delts, or triceps compared to doing pushups with each hand on a ball (less stability). The ball pushup had a far larger activation of the pec (81% vs. 61) with similar numbers for delts (individual fibers arrangements were not assessed as in the study above) and triceps. The ball pushups had greater activation of the various abdominal muscles as well.
