Postural Asymmetry (3) – Why One Shoulder Is Lower Than the Other

In this article, we will focus on asymmetry in the ribcage area. This asymmetry is not an isolated issue of a single body part, but part of a broader postural chain that rotates the body to the right, as we explained in the previous article.

Due to this overall right-oriented pattern, the trunk begins to rotate back to the left approximately from the level of the T8 vertebra (the mid-thoracic spine, which also corresponds to the upper attachment of the diaphragm). This represents a compensatory mechanism through which the body attempts to counterbalance its overall rightward orientation and maintain equilibrium.

Typical Signs of Ribcage Asymmetry

• Asymmetrical shoulder position, where one shoulder may be lower than the other

• The left side of the ribcage tends to be more expanded

• The right side of the ribcage tends to be more compressed

• The right shoulder is often rounded and positioned more forward, which is associated with limited anterior expansion on that side

  

Which Muscles Maintain the Ribcage in a Rotated Position

The rotated position of the ribcage is maintained by increased activity of certain muscles and fascial structures, which are typically more active on the right side and together form a functional chain known as the Brachial Chain.

This chain includes:

• anterior and lateral intercostal muscles

• deltopectoral fascia

• suprapleural fascia (Sibson’s fascia)

• transversus thoracis

• sternocleidomastoid

• scalene muscles (anterior, middle, and posterior)

• diaphragm

How to Address Ribcage Asymmetry

If we want to gradually improve this asymmetry, it is important to understand that the body functions as an interconnected system. The position of the ribcage is closely related to the position of the pelvis, the spine, and breathing mechanics.

Therefore, we cannot focus only on the ribcage itself — the pelvis and the ability to shift weight between the right and left sides also play a key role.

When it comes specifically to the ribcage, the main goal is to support:

• anterior expansion of the right side of the chest

• posterior expansion of the left side of the chest

  
  

Right Side – Restoring Anterior Expansion

On the right side, the goal is to help restore anterior ribcage expansion during inhalation and improve scapular stability on the ribcage.

Key muscles involved include those that assist with external rotation and proper positioning of the scapula:

• serratus anterior – supports scapular external rotation and stabilizes it against the ribcage

• lower trapezius – contributes to scapular external rotation and shoulder girdle stability

• long head of the triceps brachii – contributes indirectly to scapular positioning

Activating these muscles can help create better support for the scapula and allow the right side of the ribcage to expand more effectively during breathing.

Left Side – Restoring Posterior Expansion

On the left side, the focus is on improving the ability to move the lower ribs  inward during exhalation.

Key muscles include:

• internal oblique (obliquus internus abdominis)

• transversus abdominis

These muscles help stabilize and “close” the left lower ribs, which is essential for proper diaphragm function and overall ribcage mechanics.

Additionally, it may be beneficial to activate:

• serratus anterior, which supports protraction of the left shoulder and helps the scapula better integrate with the ribcage

Breathing and Exercise Examples

Breathing is a key component when working with the ribcage. The diaphragm influences the position of the ribs and spine and helps regulate pressure within the thoracic and abdominal cavities.

The goal is to gradually restore the ability to use both sides of the ribcage during inhalation and exhalation, which can improve the position of the scapulae, shoulders, and overall posture.

In practice, this is achieved through specific breathing and postural exercises that combine ribcage positioning, pelvic control, and trunk rotation. These exercises help not only improve ribcage expansion, but also restore controlled trunk rotation and better weight transfer between sides.

One example is the exercise All Fours with Left Trunk Rotation, which primarily focuses on:

• improving posterior expansion of the left ribcage

• enhancing anterior expansion of the right ribcage (if the goal is to emphasize anterior expansion, the exercise can be performed with a more neutral spine rather than a rounded thoracic position)

ALL FOURS WITH LEFT TRUNK ROTATION

Starting Position:

Start on all fours with hands under shoulders and knees under hips. The head remains neutral. Place a block or book (1–2 cm high) under the left hand to rotate the trunk slightly to the left.

Execution:

Shift the center of mass slightly forward so most weight is on the hands. Slightly round the upper back, and with the exhale, tuck the pelvis and activate the obliques. During the inhale, gently press both hands into the floor and focus on expanding the left upper back with air. With each inhale, continue rounding the upper back and increasing posterior expansion.

Common Mistakes:

• Shrugging the shoulders. • Losing the slight posterior pelvic tilt.