The deltoid muscle is divided into anterior bundle, middle bundle and posterior bundle, in which the middle bundle is an important part to determine the shoulder width. According to the anatomical position and main functions of deltoid muscle, it can be concluded that one of the most effective training actions to widen shoulders is to press the neck with barbells, as shown in the figure.

The key points to pay attention to are: keep your back naturally straight, and don't put the barbell too low behind your neck, otherwise it will easily hurt your joints, relax the muscles at the upper end of deltoid muscle and reduce the training effect.

In addition, it can also be combined with dumbbell pressing and dumbbell side lifting, which is very effective for the growth of the middle bundle of deltoid muscle.