I do however have one particular area of my programming in which I do get very specific about which grip is to be used and this is with the majority of pressing movements. I prefer that my clients do a good amount of their initial pressing movement with neutral hand positions. This is what I refer to as the position between a supinated wrist and a pronated wrist where the palms face inward toward one another. I sometimes allow my more experienced clients to use a hybrid position where the wrist is pronated to about a 45 degree angle to the contact of stability (this is what I refer to as the bench or ground depending on your orientation to gravity and the exercise being performed). Just about every client I have programmed for has asked me why I prescribe this hand position over the much more popular and more frequently practiced pronated grip (palm is facing away from you). The initial question asked every time is "does this work a different part of my muscle". Now while changing hand position will shift the percentage of muscle fibers recruited within the stimulated muscle, I often don't share that with them because I do not want them getting into a mindset that they need to do 6sets of a pressing motion all with various hand positions in order to sculpt the most beautiful well rounded muscular physique. I mean come on last time I checked your goal sheet you didn't put down that you want to be the next Mr. Olympia. While grip variations and angle adjustments are great for a change of pace for most of my clients I want their focus on the holistic movement not what part of their muscle is being innervated. So normally I lie to them (its for your own good people don't hate). I tell them no it is not because it works a different muscle or part of a muscle, the reason I have you use that hand position is because it will end up saving years of wear and tear from being piled on to your shoulders. So let me explain my explanation a little further so everyone understands why a neutral grip hand position is more beneficial to shoulder health than a pronated grip hand position.
Now I know I have made the focus of this post the differences in hand positions but let me let you in on a little secret really I could care less where an individuals hand is position during a pressing movement. What I really care about is the degree of the angle of abduction from the elbow to the side of the body. You see the further the arm moves away from the body the greater the degree of external rotation in the shoulder. When the shoulder is forced to maintain a high degree of external rotation for a long period such as during a set of the bench press with the arm abducted from the side of the body more than 45 degrees it places much stress on your rotator cuff to stabilize the head of the humerus in its very shallow socket on the glenoid. Now add increased load to that position such as two 45 pound plates in the bottom position of the bench press and you have a bad situation for any body lacking proper strength in the rotator cuff (which is a large amount of the General Population Clients I see). Due to this situation I find myself being very particular about what angle my clients abduct their arm from their side to perform a pressing movement.
You are probably think but wait you were just talking about hand positions and now you have jumped to the angle at which the arm is abducted aren't those two different factors that play a role in exercise technique. Well yes they are two separate factor that are not directly related. You can maintain pronated grip with keeping the angle of arm abduction in a press very small, such as during a close-grip bench press. But what I have found is that during dumbbell pressing movements whether they be horizontal or vertical when I cue my clients to use a neutral grip they automatically assume a preferable angle of abduction which I place somewhere less than or equal to forty five degrees. Now when we are talking barbell variations of pressing movements a better cue is to adjust the grip width to allow the elbows to get to a preferred angle of abduction.
Anyway the take home message here is that I find a neutral grip when performing dumbbell variations and narrow grip width when performing barbell variations to be more shoulder friendly because it allows for a more preferred angle of abduction between the arm and the rest of the body. This smaller angle places the shoulder in less external rotation and places less stress on the small tiny rotator cuff muscles that your shoulder joint relies on heavily to maintain the humeral head in a stable position against the glenoid. So for the majority of pressing movements I would recommend a neutral hand position. Use a pronated grips sparingly and accordingly.