Last week we broke down the squat and its influence on our joints and muscles.
The main strength training exercise we will look at today will be….
The Dumbbell Chest Press
There are many variations of the chest press and most of them will follow the same basic guidelines we cover today, but I choose the dumbbell press because it is a common upper extremity exercise in a lot of strength training programs. It is commonly classified as a horizontal push in terms of its movement.
Let’s break it down:
The top: lying supine, straight arms with dumbbells above chest, slightly retracted if range is available
The middle: the arms begin to bend/fold and the weight descends toward the shoulder
The bottom: the end range of motion at the shoulder joint is achieved and then the arms start to straighten out to raise the weight back to the top position
Diving deeper, what is happening to the joints and muscles? As we discussed last week, we already know muscles have one job, which is to contract. Also, joints are the connection of bones and create an axis, which is how we are able to fold during the squat. The joints we will look at are the shoulder and elbow (not that those are the only joints involved).
Here is what is happening during each position:
The top: Specific muscles that influence the shoulder and elbow are co-contracting to maintain the top position. The contraction is ‘orchestrated’ by the brain and very precise to that position.
The middle: Once the weight starts to lower, the muscle around each joint is now responding to the change in position (new external force or torque loading), and creating the necessary contraction (eccentric/concentric or lengthening/shortening) in response to that new torque loading and what your body is trying to do (arms going up/down).
The bottom: Now that the eccentric portion is complete, your muscles must create enough torque (internal torque) to move the mass (dumbbell) back to the starting position
Now that you have an idea of what’s going on during the different positions of a chest press, let’s take a look at what is happening from a challenge or stimulus standpoint (or better yet the resistance) at each position.
The Top: We can see that the resistance (represented by the green line) goes straight through the joints (shoulder and elbow) at the top position. This means that there is little to no challenge since there is no external torque loading at the shoulder or elbow...remember torque is not just the amount (pounds on dumbbell), there is also a distance component (also known as a moment arm; represented in red and pink for the shoulder and elbow respectively).
The Middle: As you begin to lower or fold to the bottom position, that distance from the axis begins to change. This means that the muscles around the joints (shoulder and elbow) must create an internal force or torque in response to the external force or torque.
The Bottom: The moment arm at the shoulder reaches its longest point, meaning the resistance it at its highest point at this position. There is also a small moment arm to the elbow (depending on where the dumbbell is placed), meaning that some elbow musculature must create an internal torque to match the external torque and maintain the dumbbell’s position.
So why does this matter?
There are some things to consider when executing this exercise and also from a programming standpoint.
As with most multi joint pushing exercises (squat, shoulder press, leg press, etc.) there is a specific strength component that we must take into account. We are strong at the top position, mostly due to structure/joint positions, and weak at the bottom position, mostly due to tissue length and internal moment arms of the muscles. Given this info, we can see that a dumbbell chest press does not match up well, since we have already determined that it is easy at the top and hard at the bottom.
If we are truly trying to bias the pec major (a big influencer in this exercise/joint motion) then we are missing a few parts of the range to challenge it. It has minimal challenge in its shortened position and a whole lot of challenge in its more lengthened position. Some complimentary exercises (cable chest flys, chest fly machine, or some variation of the chest fly….other than Dumbbell chest fly) will be necessary to create a ‘full range’ challenge.
I hope this helps see the Dumbbell chest press from a different perspective, rather than just mindlessly executing it because it’s in the newest, trendiest program. Remember, it’s all about forces and torque when we are looking at how the body will respond to a specific resistance/exercise. Next week we will go even further and have some tips and considerations on how execute both the squat and the chest press. Have a great rest of the week!