Excerpts from Strength Training
in Complete Conditioning for Baseball by Jeff Forney

Core Area
The abdominal muscles, back muscles, gluteals, hips, and chest and shoulder muscles make up what we call the core area of the body. The core is the main target area for athletic performance. These areas must be well conditioned and strong for optimal performance. The primary function of the core is to transfer force generated by the lower body to the chest, shoulders, and arms, where the force is applied. The action and strength of this core area contributes to over 50% of the force generated in throwing and hitting. This area also stabilizes the trunk area when running. Because of its great importance in baseball, we'll say quite a bit about strengthening the core area. First let's focus on the core areas that apply in the weight room.

Back Region
The upper and lower back play key roles in baseball as they are involved in all throwing and swinging actions. The back makes up a huge muscle group that includes the rhomboids, latissimus dorsi, rotator cuff group, trapezius, and rear deltoid. Neglecting this group will leave you weak and open to injury. The muscles of the back provide the agonist/antagonist balance for all major pressing and pulling actions.

Auxiliary Muscles
So far we've focused on the core area of the muscles - the legs, back, abdominals, chest and shoulders. Now we'll turn our attention to the smaller, secondary muscles of the upper body: the biceps, triceps, and forearms.