Movement Analysis Considerations
Increased Range-of-Motion
The dumbbell applications allow for the benefit of increased range of motion (relative to the Barbell Chest Press exercises) and thus provide for more stretch at the bottom of the lift. The concept of stretching the muscle is significant with respect to enhanced growth and development potential. Increasing the ROM of the movement necessitates that the muscle must contract over a greater distance and for a longer duration which would enhance the potential for muscle hypertrophy.
Variation in Fibre Recruitment
As well, dumbbell applications involve a slightly different fibre involvement due to the required balance factors associated with dumbbell training. Dumbbell training also provides for flexibility in the movement applications as twisting actions, (altering the pronated grip to a semi-pronated grip) can be used to great effectiveness. The twisting actions activate additional muscle fibres and provide accentuation of the medial portion of the chest which produces a deep crevice between the pectoral muscles. The significance of the twisting action is also found in the fact that such movement more highly activates the pectoralis minor which produces a larger base and increases the depth and girth of the chest.
Outside-to-Inside Movement Application
The utilization of the dumbbell press provides for a wide-to-narrow line of application. The commencement of the exercise sees a wide position of the hands. As the weights are contracted through the concentric contraction the hands are brought in toward the mid-line of the body so that the completion of the movement the dumbbells are positioned over the sternum. The drawing-together action involves adduction of the arm at the shoulder-joint which incorporates accentuated activation of their pectoral muscles. The wide position accentuates the lateral region of the chest while the narrow position accentuates the medial portion of the chest. The outside-to-inside movement provided by the dumbbell application thereby provides for stimulation of the entire chest area which further promotes muscle hypertrophy.
Dangers Associated with Dumbbell Training
Unfortunately, there is also a risk-of-injury factor associated with dumbbell training and as such, extreme care must be taken in order to ensure optimum growth and development and reduced injury-risk potential. While the dumbbell pressing movements are considered "isolation" exercises there is still a "power" component associated with the pressing action. The dangers of working against gravity remain consistent and both external and internal injury risk is potentially high.
Lack-Of-Balance Factor Presents Risks
While one of the benefits attributed to dumbbell training is seen with the requirement of the muscles to contract in effort to provide balance (as well as in contracting to move the resistance against gravity) the lack of "built-in" balance as provided by the barbell application, exposes the dumbbell application as even more risky. The dumbbells are independent of one another and require full concentration from the trainee to remain in the desired location throughout the movement application.
Lactic-Acid Build-Up More Significant
Dumbbell training places increased significance on the requirement of devoting strong concentration into the movement application. As lactic-acid builds up in the muscle during the completion of the set and sporadic muscle response is experienced, there is a greater risk of losing control of the weight than in barbell training where a balance factor is provided by the bar. With no such "built-in" balancing component, the dumbbell applications exert a greater need for strong concentration to be applied to the movement in order to overcome the problem of neural-impulse deflection associated with lactic-acid build-up. Both internal and external injury risks are significantly increased under conditions of lactic-acid build-up and all-out attempts to "make the set" when dumbbell training can prove to be disastrous.
External and Internal Injury Risk
External Injury-risk
External injury risk can be high if less than full concentration is devoted to the movement as the weights can come down off-line into the facial area of the trainee. Over-zealous attempts with ill-advised poundages and haphazard or casual training applications could easily result in the dumbbells collapsing in toward the face or skull due to the fact that the stabilization benefit associated with barbell training is not available. The trainee is forced to control each dumbbell independently.
Internal Injury-risk
The lack of "built-in" balance associated with dumbbell training also presents a risk that the dumbbells will sway outward during the movement application. Frequently, when fatigue sets in during the set, there is high risk that there will be a loss of control of the line-of-application of the movement. One or both of the dumbbells can swing outward away from the desired line of application. If the dumbbells are allowed to "free-fall" out of line, the ligaments and tendons, as well as the muscles of the shoulders, can easily become stretched or torn as a result.
Dangerous "Whipping" Action
If one side sways off-line to the extent that the trainee loses control completely and drops the dumbbell, there is resulting "whipping" action of the body that occurs that is even more pronounced than that which is experienced when a loss of balance of one side of the barbell is experienced. The opposite-side arm is violently forced outward which exposes the shoulder region to permanent injury risk. As well, the violent recoiling effect exerts severe torque on the vertebral column which can result in neck and spinal injuries.
