The bench press is one of the most popular gym exercises. As a compound exercise, it brings multiple muscle groups—including the delts and triceps—into play as prime movers and stabilizers that must work together to balance, direct movement, and generate force. It’s easy to think that the activity of the primary muscle groups involved would simply increase as the load increases. However, recent research calls this into question.
A study published in the Journal of Strength & Conditioning Research examined the impact that increasing loads has on the activation and contributions of the chest, front delt, triceps, and lats during the bench press. Subjects performed consecutive sets of a single repetition of a bench press with an increasing load (about 70, 80, 90, and 100% of their 1RM) while electromyography (EMG) readings were taken from the aforementioned muscle groups.
To the researcher’s surprise, the chest, which is normally the prime mover, changes to a “supportive” prime mover when the load reaches maximum. In other words, as the weight increases from 80 to 90 to 100% of the subject’s 1RM, the chest’s contribution gives way to the front delts and triceps, which essentially take over as primer movers.
As the weight used during bench press increases from about 70 to 100% 1RM, the shoulders and triceps become the prime movers of the exercise.
The activation of the chest peaked before reaching 100% 1RM. This tells us that the most efficient way to train the chest is not with maximum loads. To put the focus on building the chest, 75 to 85% 1RM is best. The authors of the study also con rm that to protect the shoulders from injury while maintaining the effectiveness of the exercise, the bar should be brought down to the nipple line, and the hand placement should be within 1.5 times the biacromial width, or the width from the far end of the right collarbone to the far end of the left.