Most of us naturally perform upper body exercises with an overhand or pronated grip (palms facing out). This grip positions the body to use the biggest muscles in their most mechanically advantageous position during pressing or pulling movements. But this position also creates excessive external rotation of the shoulder, which I’ll explain, is dangerous. So what about doing the opposite grip, the supine (palms facing us)? Extreme internal rotation is the result here and is just as problematic.
At rest, only 20-30% of the humerus (upper arm bone) is in contact with the glenoid fossa. It’s a vulnerable area. There is even less contact with the shoulder is rotated. Thus, during rotation, the load is carried by the relatively small rotator cuff muscles to keep the shoulder intact. This causes the subacromial space (between the humerus and acromion) to compress, often resulting in shoulder injuries.
Using a NEUTRAL GRIP (palms facing each other) removes the rotation of the humerus, allowing maximal contact between it and glenoid fossa. This creates more space, allowing muscles and tendons of the rotator cuff muscles to move more freely.
Another tip to save your shoulders from undue strain is to move your arm angle forward about 10-20% during vertical presses or pulls. Thus, your elbows, forearms and hands will be slightly in front, rather than parallel to your shoulders. You won’t be pressing or pulling straight up or down and will eliminate the shearing which occurs at the acromion otherwise. You will probably have to lean back slightly depending on your shoulder mobility.