When we talk about core strength postpartum, the conversation often centres on abdominal exercises and direct core work. While those can play a role, true core function depends on a broader foundation. One of the most important, and overlooked pieces, is rib mobility.

If the ribs don’t move well, pressure management becomes inefficient. The diaphragm can’t descend or expand fully, the pelvis struggles to maintain a stacked position, and the core is forced to compensate with tension rather than coordination. Over time, this shows up as upper-ab gripping, shallow breathing, reduced strength output and a core that likely plateaus is strength.

Before loading the core after childbirth, we need ribs that can expand, rotate, and move relative to the pelvis.

Why Rib Mobility Is Often Limited Postpartum

During pregnancy, the ribcage adapts to accommodate a growing uterus. The ribs often flare and widen, the thoracic spine becomes more extended, and breathing shifts toward the upper chest and belly.

Postpartum, those changes don’t automatically reverse.

Common patterns I see include:

• Reduced posterior rib expansion (the ribs don’t move well into the back)
• Limited lateral expansion (side ribs stay rigid)
• Over reliance on the upper abdominals to manage pressure. Often see middle/upper abs engage first in breathing and core exercises.
• A diaphragm that struggles to move through its full range.

Instead of the ribcage moving freely with each breath — expanding to take in pressure and recoiling to manage it — the body often defaults to belly only breathing or holding tension to feel stable. Stability is created through rigidity rather than movement.

This can show up as:

• Persistent gripping through the middle/upper abdominals
• Shallow or chest dominant breathing
• A plateau in core strength or a persistent ‘lower belly pooch’
• Feeling unstable or disconnected even with light loads i.e pressure leaks (coning/doming) from mis managed pressure.

What’s missing isn’t just strength, it’s also available movement. When the ribs can’t expand laterally or posteriorly, and the thoracic spine doesn’t allow the ribcage to move, the system loses its ability to manage pressure dynamically. The core then compensates by increasing tension to create stability.

Restoring rib mobility gives the body another option: to stabilise through coordination, breath and load sharing.

The Role of Rib Expansion in Core Function

The ribcage plays a critical role in how pressure is managed through the trunk. For the diaphragm to function optimally, the ribs must be able to expand in multiple directions vs just forward.

Lateral Rib Expansion

Lateral rib expansion allows the ribs to move outward to the sides during inhalation, giving the diaphragm the space it needs to descend and function efficiently. When this side-to-side movement is available, pressure can be distributed more evenly through the abdominal wall and pelvic floor, rather than being managed by excessive abdominal tension. This supports better rotational and frontal plane control and reduces the tendency for the upper abdominals to dominate core stability. When lateral expansion is limited, breathing becomes narrow and the body often compensates by bracing to create a sense of stability instead of allowing the core to coordinate dynamically.

Posterior Rib Expansion

Posterior rib expansion refers to the ribs moving into the back of the ribcage, an area that is commonly restricted postpartum. When the ribs can expand posteriorly, the diaphragm gains better access to its posterior fibres, allowing pressure to be managed with less reliance on abdominal tension. This helps reduce excessive lumbar extension and rib flare, supporting a more neutral relationship between the ribcage and pelvis. As posterior expansion improves, the core can engage in a more balanced way without over-recruiting the upper abdominals to create stability.

When both lateral and posterior rib expansion are restored, the core works more efficiently through coordination and breath.

Why Thoracic Mobility Matters Here

Rib mobility doesn’t exist in isolation. The position and movement of the ribs are directly influenced by how the thoracic spine moves — or doesn’t move.

When the thoracic spine is stiff, particularly in flexion and rotation, the ribcage loses its ability to move three-dimensionally. This limits the ribs’ capacity to:

• Expand laterally to support efficient diaphragm movement
• Rotate smoothly to allow trunk rotation and load transfer
• Move relative to the pelvis during breathing and dynamic movement

Postpartum, the thoracic spine often remains biased toward extension. This extended posture restricts access to the back and sides of the ribcage, making posterior and lateral expansion more difficult. As a result, the body frequently manages pressure by increasing abdominal tension, rather than allowing the ribcage, diaphragm, and pelvis to work together.

The goal here is not aggressive stretching or forcing the ribs into position. Instead, we want controlled thoracic mobility that:

• Restores access to thoracic flexion where it’s limited
• Allows rotation to occur without compensations through the lower back or pelvis
• Supports rib expansion and breath mechanics rather than overriding them

When thoracic mobility improves alongside rib expansion, the core becomes more adaptable and responsive. This creates a system that can manage pressure, rotation, and load more efficiently — and sets the foundation for meaningful strength work in later phases.

Setting the Foundation

This first phase focuses on restoring rib and thoracic movement to improve how the diaphragm and ribcage manage pressure. By creating more available expansion and rotation, the core can stabilise through coordination rather than constant tension.

With this foundation in place, strength training becomes more efficient, more sustainable, and more supportive of long-term core health.

Rockback Breathing

This position encourages posterior rib expansion while keeping the pelvis relatively organised. The rockback reduces extension bias through the spine and allows the breath to expand into the back of the ribcage, improving diaphragm function and reducing reliance on abdominal tension to create stability.

Side-Lying Breathing with Forward Reach & Rib Smash

Side-lying positions make lateral rib expansion easier to access. The forward reach helps guide the breath into the side and back of the ribcage, while the rib smash provides tactile feedback to encourage movement into areas that are often restricted postpartum.

Short Lever Side Plank with Forward Reach & Ball Press

This variation introduces low-level lateral core engagement while maintaining rib mobility. The forward reach encourages posterior rib expansion, while the ball press through the reaching arm increases serratus engagement, helping the ribcage protract and move more freely over the pelvis without driving excessive abdominal bracing.

Hands and Knees Breathing with Band Feedback

This option reinforces posterior rib expansion with external feedback. The band guides the breath into the back of the ribcage, helping reduce upper-ab dominance and improving awareness of rib movement in a more functional, upright-supported position.

Long Sit with Banded Serratus Reach

This drill targets rib mobility through shoulder and thoracic movement. The banded reach encourages serratus engagement, supports rib protraction, and improves lateral and posterior expansion while maintaining an organised rib–pelvis relationship.

Open Book with Banded Rotation

Adding band resistance to the open book improves thoracic rotation while encouraging the ribs to move with the breath rather than compensating through the lower back. This supports smoother rib–pelvis interaction and prepares the system for rotational loading later in the series.

Final Thoughts

Rib mobility is a foundational piece of core strength that’s often overlooked. When the ribs can expand, rotate, and move relative to the pelvis, the core can manage pressure with less effort and more efficiency. This creates a system that’s better equipped for strength training, impact, and long-term resilience — especially postpartum.

This first phase focuses on restoring that movement and capacity. In the next part of the series, we’ll build on this foundation by integrating rib mobility into strength and stability work, bridging the gap between breath, movement, and load.

If you want to follow the full 3-part Rib Mobility for Core Strength series, including the full exercise progressions and how they fit into complete workouts, you can access it inside the Lift with Emily app. The series is programmed as part of a broader approach to core, strength, and postpartum training, so you’re not just doing isolated drills — you’re building a system.