Where the Muscle Is Located
The serratus posterior inferior is a thin, quadrilateral muscle situated in the lower portion of the back. It originates from the spinous processes of T11 to L2 and inserts into the inferior borders of ribs 9 to 12. Its primary function is to depress the lower ribs, aiding in forced exhalation. It does not directly contribute to neck or head extension and rotation, though it supports spinal stability during breathing and trunk movement.
Different Ways to Engage
- Resisted Exhalation: Place a band around your ribs or hold a light weight on your chest while exhaling deeply against the resistance, activating the muscle through rib depression.
- Bent-Over Breathing Drill: In a hip-hinged position, take deep breaths and focus on drawing the lower ribs inward during exhalation.
- Isometric Rib Hold: Wrap your hands or a strap around your lower ribs, breathe out fully, and hold the ribs in the depressed position.
- Quadruped Breathing: From an all-fours position, perform full exhalations while engaging the lower ribcage, targeting deeper stabilizers including the serratus posterior inferior.
- Low Cable Pulls with Rib Control: While performing a low cable row, emphasize rib control during exhale and trunk stabilization.
How Long to Hold Flex for Muscle Growth
- Beginner: 5–8 seconds during exhalation, 2–3 sets
- Intermediate: 10–15 seconds with added tension or postural challenge, 3–4 sets
- Advanced: 20–30 seconds, integrating breath control with functional movement, 4–5 sets
Since it plays a supporting role in respiration and trunk movement, this muscle responds well to moderate frequency (3–4 times per week) and controlled, breath-based tension.
Different Levels of Skill
- Beginner: Focus on breath control and learning to feel the ribs move with proper exhalation.
- Intermediate: Use postural variation (seated, bent-over, quadruped) to challenge the ribcage mechanics.
- Advanced: Combine rib control with loaded trunk stabilization and deep core activation.
How It Supports Other Muscles
- Diaphragm: Works in tandem during exhalation to control intra-abdominal pressure.
- Transversus Abdominis and Internal Obliques: Supports core function and trunk stability during breathing and movement.
- Latissimus Dorsi: Stabilizes rib positioning during pulling and spinal extension.
- Erector Spinae and Multifidus: Contributes indirectly to maintaining spinal alignment and controlled movement through breath-synchronized tension.
Although the serratus posterior inferior is not directly involved in neck or head movement, it plays a foundational role in breath mechanics and trunk support, especially during forceful exhalation or loaded movements. Strengthening and training it helps stabilize the lower back and improves respiratory efficiency under physical strain.
