The most active portion of the triceps was the long head, which is even more active with a narrow grip. This is true even when overhead pressing, assuming the elbows are fully adducted. This is secondary to the greater degree of elbow flexion, in which the triceps brachii functions as the agonist.
The anterior deltoid will be more active the more the trunk is inclined, as well as being more active with a wider grip. This is due to the fact that the anterior deltoid is not merely an flexor of the humerus, but also an abductor of it. Wide hand spacing during a vertical press will cause mainly glenohumeral abduction, whereas with a narrow grip the primary movement is flexion.
The sternocostal head of the pectoralis major is little affected by hand spacing, but is directly affected by trunk inclination. The greater the inclination, the less the activation. There is also a slightly greater activation of this muscle with a wider hand spacing, due, in general, to the fact that with a wider grip, the elbows tend to move away from the midline of the body, which increases the degree of horizontal flexion of the humerus.
The clavicular head of the pectoralis major is affected by both hand spacing as well as trunk inclination. The narrower the grip, the greater the activation, as well as the greater the inclination, the greater the activation. There are several factors for this, including the fact that vertical bar displacement is greatest during an incline press. This is also due to the fact that the clavicular head is involved in horizontal flexion and adduction in addition to pure flexion. The clavicular head will maintain its function as a flexor of the glenohumeral joint until humerus moves above the horizontal position. This is why it is rather inactive when the torso is vertical, as little flexion is occurring.
The latissimus dorsi is highly active at the initiation of the concentric phase, with greater activity the closer the elbows are maintained to the torso, due to the degree of adduction required. The latissimus dorsai is an extensor at the glenohumeral joint as well as being a humeral adductor, which explains its activity during every type of pressing.
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