The parallel bar dips action is similar to the action of declined bench press with the complete anatomical movement / action of the pectoral major muscles, which is throwing the thing outward and downward. It leads to complete contraction and relaxation of the pectoral muscle as a major mover and as minor movers the triceps muscles and the interior deltoids muscles are in great action. Once the person can do more than 20 repetitions of dips then he needs to put up some weight across his belt for great exercise load.
To get the maximum benefit of power dips on chest one should be leaning forward to the maximum angle and then pushing one self to the top starting position. If one wants to get stronger triceps and shoulders out of this movement one should keep the chest up and concentrate over the triceps movements.
One can use some dumbbells stucked to the feet or an exercise belt with a clamp to hold some weight plates for extra load. This leads to better muscle building repetition from 6-10 reps in every sets. Perform 1-2 sets after your bench presses and incline presses 2-3 times a week.
