Here's how to ramp up the muscle-building effects of the standard dumbbell bench press.
Push the dumbbell heads together and contract through the pecs. A very significant benefit of isometric training is that it produces a greater level of activation than any other type of contraction. One of the main benefits is that the body is able to activate nearly all the available motor units, something that's usually very difficult to do.
Combining both slow eccentrics and isometric work on each rep creates a highly effective and challenging exercise. You get the benefits from both types of training. This can be very taxing if done correctly, so try to get a partner to keep you honest on both elements of the exercise.