Grip width only affects the lats or pecs differently if the elbow is moved into a different plane of motion. There is no need to do incline press, shoulder press, and overhead db press all in the same workout, not to mention 3 times per week. If you insist on doing all of these shoulder movements you need to arrange an alternating workout schedule. Do flat bench and shoulder press on one workout, then dips and incline press on the next. Then just alternate between the two exercise routines each workout. The same goes for biceps. If you are training back properly, there is no need to do two different curling movements in a single workout. As with shoulders, alternate between curling movements from workout to workout.
How does grip width and different angles change the stimulus?
In general, when person moves their grip from wide to narrow, the elbows will pull in towards the side of the body during the pulling motion. This changes the line of pull transferred to the muscles of the back and shoulders.
It also changes the degree of stretch, or the length of the muscle during the contraction.
As for recruitment, the innervation of the lats is from the thoracodorsal nerve. With practice you can lean to control the lat, apart from the surrounding musculature. This however, isn’t necessary for typical lifting, nor is it possible with heavy loads.
Think of the lat as a sheet that can experience different levels of tension depending on how you stretch it.
Training a muscle in a lengthened position will cause more microtrauma than training it in a shortened position. Decline curls stretch the short (inner) head more than the outer (long) head of the biceps simply due to their different origins. The short head originating at the coracoid process and the outer head attaches to the humerus. So the outer head doesn’t stretch as the upper arm is moved away from the center line of the body whereas the inner head does.
The pec minor actually lies beneath the pec major so you don’t actually see it. The pec minor attaches to the ribs and the coracoid process. The pec minor simply pulls the shoulder girdle forward. The pec major moves the upper arm because of its insertion at the humerus.
Studies have shown that the upper portion of the pec is usually just as active as the lower portion during heavy flat bench. However, there is some benefit to doing incline bench because it seems to help build the clavicular portion of the pecs and the front delts.
Nothing isolates the “inner” portion of chest. The myth arose out of the “sensation” that one feels as the pec becomes cramped while contracting it (with the arms brought close together in front of the body and flexed hard). Isolating the inner pec is like isolating one portion of a rubber band as you stretch it from either end. Now, there are differences in the way the muscle experiences stress due to the convergence of the fibers near the insertions at the musculo-tendonus junction...but that’s more detail than is necessary.
One thing everyone should keep in mind. The distribution of androgen receptors is not even throughout the body. There is a greater density of androgen receptors on the shoulder girdle (delts, traps, upper pecs). You will notice, that once a guy begins to use androgens, he almost immediately grows traps and delts. In short, there are disproportional increases in muscle mass
