Introduction
Welcome back. In our last lesson, we created a precise map, linking specific exercises like incline presses, flat flies, and dips to the anatomical divisions of the pectoralis major they target. We established that the key to biasing a muscle region is to align the direction of resistance directly opposite the muscle's fiber direction.
Today, we'll use that anatomical knowledge for a different purpose: diagnostics. It’s one thing to know the right exercise, but it’s another to execute it for maximal results. A common frustration for many trainees is performing chest exercises but feeling them more in their shoulders or triceps. Our goal in this lesson is to analyze common chest training mistakes from an anatomical perspective. We will move beyond simple "do this, not that" advice and delve into the biomechanical why behind these errors. Understanding these root causes will transform you from someone who just follows a program into a coach who can identify and solve movement problems.
1. The Most Common Culprit: Excessive Anterior Deltoid Dominance
Many people complain, "I only feel bench presses in my front shoulders." This isn't just a subjective feeling; it's a biomechanical reality that stems from specific technical flaws. When the anterior deltoid takes over, it's because the movement pattern has shifted to favor its mechanics over those of the pectoralis major. Let's break down the primary causes.
Anatomical Cause #1: Incorrect Arm Path (Elbow Flare)
The most direct cause of anterior deltoid dominance is an incorrect arm path, typically characterized by flaring the elbows out to the sides, creating a 90-degree angle between the torso and the upper arm.
Recall the fiber direction of the sternal (middle) pec: they run mostly horizontally. To challenge them, we need to bring the arm across the body (horizontal adduction). When you flare your elbows, the arm is no longer moving primarily in the transverse plane. Instead, it moves in a path that aligns almost perfectly with the fibers of the anterior deltoid, which run down the front of the shoulder. Your body, being an efficient machine, will simply use the muscle that has the best leverage for the path you've chosen.
STOP Doing Dumbbell Press Like This (5 Mistakes Slowing Your Chest Gains)
The video 'STOP Doing Dumbbell Press Like This' by Jeremy Ethier provides an excellent visual and anatomical explanation for this first mistake.
Watch from 00:20 to 01:29. Pay close attention to how he contrasts the flared-elbow path with the correct, tucked-elbow path, and his explanation of how this aligns with the respective muscle fibers.
The key is to tuck the elbows to roughly a 45- to 60-degree angle relative to your torso. This slight tuck aligns the path of the humerus with the line of pull of the majority of pectoral fibers, giving them better mechanical leverage to move the weight.
Kassem Hanson of N1 Education offers a slightly more advanced biomechanical model, thinking of the rib cage as an "anatomical pulley" that changes the pec fibers' line of pull.
Is this the most important principle of chest training?
In this clip, 'Is this the most important principle of chest training?', Kassem Hanson explains why keeping the arms closer to the body improves leverage for the pecs.
Watch from 00:18 to 02:33. Focus on his concept of the rib cage as a pulley and how flaring the arms out wide results in poorer mechanical advantage for the pecs.
Anatomical Cause #2: Poor Scapular Positioning
Even with a correct arm path, the anterior deltoids can still take over if you don't create a stable base for the movement. The pectoralis major pulls the humerus towards the midline of the body. The humerus, in turn, connects to the torso via the scapula (shoulder blade) at the glenohumeral joint.
If you allow your shoulder blades to slide forward (protract) and your shoulders to round during a press, you are destabilizing this entire structure. This protraction pushes the head of the humerus forward, again shifting the joint into a position where the anterior deltoid has superior leverage.
The correct position is one of scapular retraction and depression—think "pinch your shoulder blades together and pull them down towards your back pockets." This creates a solid, stable platform from which to press, locking the shoulder joint in a position that favors the pectoralis major.
The following article provides a clear written explanation of this fault.
Muscle Breakdown: Pectoralis Major
The article 'Muscle Breakdown: Pectoralis Major' clearly explains the importance of scapular position.
Read the subsection titled 'Not Pinching Your Shoulders Together'. Notice how it directly states that incorrect scapular position reduces pectoralis major activation by increasing the anterior deltoids' involvement.
Anatomical Cause #3: Excessive Incline Angle
This mistake is specific to upper chest training. As we learned previously, a low incline (15-30 degrees) is ideal for targeting the clavicular head. If the bench angle becomes too steep (e.g., 45 degrees or more), the movement transforms from an incline press into a front shoulder press. The primary joint action shifts from a combination of shoulder flexion and adduction to almost pure shoulder flexion, which is the dominant function of the anterior deltoid.
Jeremy Ethier also covers this point succinctly in his video.
STOP Doing Dumbbell Press Like This (5 Mistakes Slowing Your Chest Gains)
Let's revisit the Jeremy Ethier video to see his take on using too high an incline.
Watch from 05:36 to 05:57. He confirms that an incline of 15-30 degrees is optimal and anything higher causes the front delts to take over.
2. The Hypertrophy Killer: Common "Cheating" Methods
The goal of hypertrophy training is to create maximal tension in the target muscle through a large range of motion. Several common mistakes, often done to lift heavier weight, directly undermine this goal by reducing muscular tension at critical moments.
Mistake #1: Bouncing the Bar off the Chest
This is a classic "ego lifting" mistake. By dropping the weight quickly and bouncing it off the sternum, the lifter uses momentum to get the bar past the most difficult part of the lift—the very bottom.
Anatomical Consequence: From our previous lessons, you know that the point of maximum stretch under load (the bottom of the press) is where stretch-mediated hypertrophy is triggered. Bouncing the bar completely removes muscular tension at this crucial point, robbing you of a powerful growth stimulus. It also risks injury to the sternum and rib cage.
Mistake #2: Extreme Back Arching
While a slight, natural arch that maintains scapular retraction is good, an excessive arch where the buttocks lift off the bench is a form of cheating.
Anatomical Consequence: Extreme arching dramatically reduces the range of motion the bar has to travel. It effectively turns a flat bench press into a steep decline press. This not only shortens the ROM but also shifts the emphasis away from the sternal and clavicular heads towards the lower, costal fibers. You are essentially doing a different, less effective exercise.
The following text explicitly identifies these faults.
Optimizing Development of the Pectoralis Major - The Sport Journal
The academic article 'Optimizing Development of the Pectoralis Major' discusses proper execution and calls out these specific cheating methods.
Read the section 'Bench Press Execution'. Note the direct warnings against 'Bouncing the bar off the chest' and 'extreme arching of the back', and the explanation that these methods reduce the workload of the prime movers.
3. The Conceptual Mistake: Chasing the "Inner Chest"
A pervasive myth in gym culture is the idea that you can isolate the "inner" and "outer" portions of your chest. This leads people to perform exercises like very narrow grip presses or focus intensely on "squeezing" at the end of a cable fly, believing this will build the line down the middle of their chest.
Anatomical Reality: A muscle fiber contracts on an all-or-nothing basis along its entire length, from origin to insertion. You cannot selectively contract only the part of the fiber nearest the sternum. The pec fibers originate on the clavicle and sternum and insert all the way out on the humerus.
The "gap" between your pecs is determined by your genetics—specifically, the shape of your muscle bellies and where the muscles insert onto your sternum. No amount of "squeezing" can change this.
Muscle Breakdown: Pectoralis Major
Let's turn back to the 'Muscle Breakdown: Pectoralis Major' article, which does an excellent job of debunking this myth.
Read the subsection 'Training Your Inner and Outer Pectoralis'. Understand why this is a myth rooted in genetics and fascial anatomy, not trainable muscle divisions.
The true path to a more developed "inner chest" is simply to increase the overall size of the pectoralis major. By focusing on progressive overload with proper form on exercises that target the upper, middle, and lower divisions, the entire muscle will grow, creating a fuller look and reducing the appearance of any gap.
Conclusion
Diagnosing training mistakes is a direct application of your anatomical knowledge. Instead of just seeing "bad form," you can now see the underlying biomechanical and anatomical reasons for it.
Key Takeaways:
- Anterior Deltoid Dominance is not random; it's a predictable outcome of specific technical errors:
- Elbow Flare: Aligns the arm's path with the deltoid fibers instead of the pectoral fibers.
- Scapular Protraction: Destabilizes the shoulder, allowing the deltoids to gain better leverage.
- Excessive Incline: Turns a chest press into a shoulder press.
- "Cheating" Reps like bouncing the bar or arching excessively are counterproductive for hypertrophy because they reduce tension and range of motion, particularly in the critical stretched position.
- The "Inner Chest" is a Myth. You cannot isolate the inner portion of the pec. A full-looking chest is the result of developing the entire muscle through its anatomically distinct upper, middle, and lower divisions.
Preview for the Next Lesson
We have now identified the most common chest training mistakes and analyzed their anatomical causes. Knowing why something is wrong is the first half of the battle. In our next lesson, we will focus on the second half: the solution. We will learn how to apply coaching cues based on anatomical intent to improve pectoralis major activation and correct the very faults we discussed today.