Biomechanics (the study of the mechanical laws relating to the movement or structure of living organisms) can be split into two main categories: Intrinsic biomechanics (the study of how the body can perform tasks or movements in relation to the individual’s mechanical make-up) and extrinsic biomechanics (the study of the most efficient way to perform a movement, relevant to sports, fitness and conditioning.) To understand effective strength training, it is important to understand the physical make-up of a muscle and its extrinsic biomechanical features. *1
This picture represents the chest muscle, split into three main parts, these are all part of the same muscle, however, we can see the alignment of the muscle fibres differs throughout. (1) has descending fibres, (2) lateral fibres, (3) ascending fibres. From this, we can see that the muscle will contract when there is transverse shoulder adduction (a movement along the horizontal plane of motion, through the shoulder joint where the rotation occurs towards the body’s midline.) Section 1, descending fibres, would assist in shoulder flexion (bringing the arm straight upwards.)
A 2014 study *3 has shown that pectoralis size is tightly correlated with 1 rep max strength on bench press, therefore powerlifting concepts (low volume, high-intensity sets) are more useful to build the chest, on the contrary to bodybuilding movements and concepts that try to reach an optimal hypertrophic rep range (most efficient rep range to stimulate muscle breakdown.) However coming back to shoulder flexion, as mentioned earlier, the upper chest is involved in shoulder flexion, therefore incorporating an
incline press would help stimulate the upper section of the muscle more thoroughly due to the increased involvement in shoulder flexion when incline pressing. This is required as when bench pressing (flat) an arch is created in the back, mimicking a decline press in some regard, therefore more of the lower section of the chest (ascending fibres) are recruited to press the weight as they have a further ability to contract and stretch during this movement.
Every muscle also has a length-tension relationship (the resting length at which it can most forcefully contract), this teaches us that a muscle can be stretched and contracted too far as to detriment strength, therefore when externally rotating the arm, the chest is lengthened slightly, which is too far, meaning that the chest is in a less optimal position to contract. However internally rotating the arm puts the chest in a more optimal position to forcefully contract, therefore internally rotating arms when dumbbell pressing at any angle and also facing palms downward when doing cable flys will increase strength.
A 2010 study *4 has outlined three main methods of hypertrophy; mechanical tension, muscle damage and metabolic stress. Mechanical tension is a major factor in this, to increase tension it is important to place the muscle under a heavy overloading stimulus (inclusion of progressive overload, increasing the weight over a period of time to put more tension on the muscle.) Metabolic stress can be achieved by using an isometric hold (keeping the muscle in a stretched position with weight for an extended period of time), this allows an increased time under tension, increasing mechanical tension and also increase fatigue throughout the muscle.
An analysis *5 on the frequency of training has concluded that training two times per week increases muscle growth.
Photo Credits due to: http://www.buildupperchest.com/best-upper-chest-workout/