Understanding the R BC Pattern

The R BC (Right Brachial Chain) Pattern is the most common upper body asymmetry pattern according to the Postural Restoration Institute. But what is it and what does it mean?

One of the most ignored and under appreciated area of the body is the rib cage. This is astounding since the rib cage is so large and connects to one of our most vital and vulnerable areas, the spine. Yet it is still often ignored despite the rib cage’s importance in shoulder, mid back and neck mechanics.

When walking everyone should have a degree of rotation occurring in the rib cage to help properly balance a person’s center of gravity over their leg. In the Right Brachial Chain Pattern (R BC) the spine is stuck twisted to the right and the rib cage is unsuccessfully trying to pull it back to the left. This pattern is usually due to an accompanying L AIC pattern in the pelvis. This twist creates the stereotypical left rib flare frequently seen in the R BC pattern.

Postural example of a Right Brachial Chain (R BC) pattern showing asymmetrical rib cage position with right rib flare and altered upper trunk orientation, commonly addressed in PRI-based physical therapy.

What does the R BC Pattern look like?

With a R BC Pattern often the right shoulder will look lower than the left (but not always). The right shoulder may roll forward and the shoulder blade will wing out making it vulnerable to a multitude of shoulder issues including rotator cuff and impingement diagnoses. The right neck muscles tend to overwork to try and counteract this sagging right shoulder and help lift the right shoulder back to level. Wether or not the neck muscles are successful at leveling the shoulders this usually just results in more neck & shoulder tension.

The R BC Pattern doesn’t always effect the right shoulder & neck, it can also effect other areas such as the left shoulder or right scapular pain (mid back).

Rear view note of a Right Brachial Chain (R BC) pattern showing asymmetrical rib cage position, right posterior rib prominence, and altered upper trunk orientation commonly addressed in PRI-based physical therapy.

Left Hamstring is tighter than right

Where did this pattern come from?

The diaphragm by nature is asymmetrical. Everyone has a weaker and longer positioned left diaphragm. The right diaphragm actually has more nerve innervation, and more connections to the spine than the left giving it more of an influence on the spine. This asymmetry is perfectly normal and natural but if this asymmetry is left unchecked by the left internal obliques and transverse abdominis (to keep the right diaphragm from over dominating, pulling the spine to the right) it can become a problem and lead to a over-dominate right brachial chain pattern.

Rib Cage Position, Breathing & Treatment

Because we are talking about the rib cage, we can’t ignore the correlation with breathing mechanics. Essentially in the Right Brachial Chain Pattern (R BC) the left diaphragm is not working as effectively as the right diaphragm to send air flow to the right upper quadrant of the lungs (think right shoulder region).

Treatment to balance the R BC Pattern involves properly retraining the left abdominals (internal obliques and transverse abdominis) to coordinate with good breathing mechanics. Then one can work on strengthening the right serrates anterior, low trapezius and triceps to encourage proper shoulder blade position and function on the thorax.

Possible Signs of a (typical) L AIC Pattern

Here are some observations that are common with this pattern:

Frontal view of a person with the trunk leaning to the right, showing a lateral weight shift.

Tends to stand on the right side

Person performing a hamstring stretch showing limited flexibility in the left hamstring compared to the right, commonly assessed in physical therapy.
Front view of a person standing on the left leg with the left hip shifted forward, showing asymmetrical pelvic position.

Left hip forward when standing on left leg

Rib cage demonstrating left rib flare, often seen in asymmetrical posture patterns assessed in physical therapy or PRI-based exercises.

Left ribs flare out

Close-up of a person standing with only the feet visible, showing asymmetrical wear patterns on the shoes.

Asymmetrical wear patterns in shoes

Feet demonstrating arch height differences, with the right foot showing a higher arch and the left foot a lower arch, often assessed in physical therapy or gait analysis.

Higher Right Arch, Left Arch Lower

Image showing a person unable to place feet or hands on the floor, demonstrating limited flexibility or mobility.

Can’t touch the floor

Person performing a squat with heels lifted and showing limited mobility in the right hip when crossing legs, often assessed in physical therapy or movement analysis.

Can’t put heels down when squatting and tighter right hip when crossing legs