Can you isolate the pecs with the dumbbell press? Not really...
Many bodybuilders regard the dumbbell press as an isolation exercise which they can use specifically to train their pectorals and to deactivate other muscle groups. This idea is only partly true, Norwegian sports scientists reported in 2011 in the Journal of Sports Sciences.
The Norwegians got twelve trained male students to do bench presses with a barbell, bench presses on a Smith machine, and dumbbell presses, all at maximal weight. Just to be sure we’re all on the same page, the latter exercise is shown above. The researchers attached electrodes to the participants' pectorals, delts, biceps and triceps so that they could measure how hard the muscles had to work.
The figure below shows that the dumbbell chest press stimulated the biceps more strongly than the regular bench press and the bench press done on the Smith machine.
The dumbbell press activated the shoulder muscles the same amount as the regular bench press and the bench press on the Smith machine did.
At the same time, the dumbbell chest press activated the triceps less than the other two exercises did.
J Sports Sci. 2011 Mar;29(5):533-8.
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