The 100 Degree Bench Press Rule

To make it short and simple… dropping your elbows below 100 degrees of flexion at the shoulder in a free weight bench press DOESN’T result in any additional activation of the target muscles, while it DOES significantly increase the risk of shoulder injury, particularly anterior ligament and rotator cuff tears (see GIFs 1 & 2 below).

Why 100 instead of 90? Because going just that little ways past 90 degrees does actually make a positive difference. But since you’re not going to be actually measuring the exact angle while you bench press… here’s a good rule of thumb you can apply:

APPLICATION: In a full range of motion free weight bench press, you should drop your elbows down to where they’re level with your back (which, unless you have a ridiculously massive chest cavity, will be about 100 degrees of flexion), but NOT any further!

This is especially important with the dumbbell bench press, since with a barbell you can’t go that much farther down anywhere before the bar hits your chest. However, with dumbbells (which overall are better for you) there’s no such built-in stopping point. 

Related Dr. Gains YouTube Videos:   
      1) BEFORE YOU BENCH PRESS, Understand the Anatomy Behind it! (Incline, Decline, Close Grip, Wide, Form)

Relevant Research Articles:     
      1) Kinematic factors influencing performance and injury risk in the bench press exercise
      2) Upper extremity weightlifting injuries: Diagnosis and management
      3)Maximal Strength Performance and Muscle Activation for the Bench Press and Triceps Extension Exercises Adopting Dumbbell, Barbell, and Machine Modalities Over Multiple Sets