One of the most fundamental rules of weight lifting is to do barbell exercises earlier in your workouts and dumbbell exercises later because you can generally press more weight with barbells than dumbbells.
Researchers from Norway compared the barbell bench to the dumbbell bench in trained weight lifters, measuring how much weight they could press for a one-rep max and analyzing the muscle activity involved in the pecs, front delts, triceps and biceps.
The researchers confirmed that 20% more weight can be pressed with a barbell than with a dumbbell. They also found that, although there was little difference in the muscle activity of the pecs and delts for both exercises, the dumbbell bench press used less triceps and more biceps.
Lifters are much stronger on barbell bench presses than on dumbbell bench presses. However, the Norwegian team also found that dumbbell presses use much less triceps muscle than barbell bench presses. This is likely due to the fact that the movement is more of an arc with dumbbells, as your arms move up and together. The barbell, on the other hand, only allows the arms to move straight up. This allows you to fatigue your triceps on bench presses first. Then when you move on to dumbbell presses, the triceps won’t be the weak link and you can focus more on the pecs.
Follow the standard practice of doing barbell bench presses first in chest workouts to maximize the amount of weight you bench press and therefore the amount of overload on the chest. Afterward, move to dumbbell presses to better focus on the pecs without the triceps being the weak link. This study sets the barometer for how much weight you should be able to use on dumbbell bench presses — 80% of your barbell bench-press weight. If you’re under this mark, work more on your dumbbell bench presses; if you are over, then work on your barbell bench presses. - FLEX