The Bench Press is one of the 4 core multi-joint lifting exercises. It is often performed during the later stages of rehabilitation following an anterior shoulder dislocation. The main muscles used during the lift include the pectoralis major, the triceps brachii and the anterior deltoids. 

Anterior shoulder dislocations typically occur during sport when the upper limb is forced into excessive abduction and external rotation (think the windup position for throwing a ball). Consequently, this is why the bench-press, which places the shoulder into a similar position can be problematic. 

Forces during the lift 
When performing the bench press horizontal and vertical forces are placed upon the shoulder, which produce a diagonally orientated (resultant) force that influences muscle loading and recruitment. 

Grip Width 
Depending on barbell grip width, this diagonal force will travel farther or closer to the body. Gomo and Van Den Tillaar (2015) determined that a grip of 2x shoulder width places greater load on the pectoralis major with the diagonal force passing farther from the body. Differentially, a grip width at shoulder width places greater load on the triceps brachii with the diagonal force passing closer to the body.

Why utilise a narrow grip? 
The pectoralis major broadly attaches from the sternum to the head of the humerus. When the muscle is activated at the lowest point of the bench press it pulls the humeral head forward, which could be problematic for an unstable shoulder joint. As a solution, Lorenz and Maddolon (2017) recommend that when initially returning from anterior shoulder instability, an athlete should perform the bench press with a grip no greater than 1.5x shoulder width. 

Rotator cuff tip 
Sufficient rotator cuff activation is also essential when performing the bench press to prevent dislocation. Assuming that the athlete has built sufficient 

strength in these muscles prior to performing the bench press, Calatayud et al. (2018) determined that firm gripping of the barbell was associated with increased rotator cuff activation and therefore shoulder stability. 

Bench press recommendations 
1. Perform with decreased depth 
2. Utilise a narrow grip 
3. Grip the barbell firmly 
4. Begin with a junior barbell weighing 10kgs 
5. Progress only 1 of the above 4 variables at a time 
6. If it seem unsafe, don’t do it and seek the advice of your Physio

References 

Calatayud, J., Vinstrup, J., Jakobsen, M. D., Sundstrup, E., Carlos Colado, J., & Andersen, L. L. (2017). Attentional Focus and Grip Width Influences on Bench Press Resistance Training. Perceptual and Motor Skills, 125(2), 265-277. doi:10.1177/0031512517747773 

Gomo, O., & Van Den Tillaar, R. (2015). The effects of grip width on sticking region in bench press. Journal of Sports Sciences, 34(3), 232-238. doi:10.1080/02640414.2015.1046395 

Lorenz, D., & Maddalone, D. (2017). Postrehabilitation Performance Enhancement Training and Injury Prevention in the Upper Extremity. Operative Techniques in Sports Medicine, 25(3), 220-230. doi:10.1053/j.otsm. 2017.07.010