**2.7. Biomechanical dysfunction begins in the sagittal plane**

The sagittal alignment of the pelvis and ribcage affects muscle length and strength throughout the body. With any activity, the positional relationships of the structures and of the muscles that attach to them change. However, when the body is at rest, the ribcage and pelvis should be in a relative sagittal neutral position with muscle groups at their resting length. In an alternating reciprocal activity such as gait, there should be a moment of relative sagittal plane neutrality as weight shifts from one side to the other.

When this relative state of neutrality is no longer possible due to overactive right-dominant patterning, the left AIC, right BC pattern takes precedence. The left hemipelvis chronically positioned in swing phase of gait is anteriorly rotated. The spine balances this forward momentum with backward tilting as tonic, shortened paraspinal muscles take on the responsibility of keeping the spine erect. The left psoas and iliacus muscles adaptively shorten as the left transverse abdominis and internal oblique muscles are stretched between their insertions on the anterior lower ribs and the now more distal iliac crest. The left anterior ribcage flares, further weakening the overstretched left lateral abdominal muscles. With diminished opposition to left diaphragm recoil, because of lengthened abdominals and a loss of ZOA, the fibers of the left diaphragm orient more vertically, and the diaphragm assumes a greater role as a back extensor muscle than as a respiratory muscle. Its directional pull on the spine is forward and upward, while the psoas pulls the spine forward and downwards. The action of these two muscle groups encourages an exaggerated lumbar lordosis, reinforced by the lumbar paraspinals [16] (see **Figure 4**).

Exaggerated lordosis in the sagittal plane precedes a cascade of compensatory muscle and respiratory activity, as the brain encodes alternative strategies for continuing upright function. Further sagittal plane dysfunction follows, for example, the development of thoracic kyphosis to rebalance weight distribution over the pelvis. Another common strategy is the development of thoracic lordosis with reversal of the cervical spine to assist inhalation as cervical respiratory accessory muscle use increases to support the inefficient diaphragm position. According to the Hueter-Volkmann Law, epiphyseal bony growth is inhibited by compression and facilitated by tractioning [40]. In a young spine, exaggerated lordosis compressing the posterior vertebral segments would facilitate the development of relative anterior spinal overgrowth (RASO). This sagittal plane flattening of the thoracic kyphosis is an acknowledged precursor of scoliosis [41, 42].

Human physiological asymmetry expressed as right-side dominance via the left AIC, right BC pattern, demonstrates biomechanical challenges to maintaining neutrality of the pelvis and ribcage in the sagittal plane. Other factors contributing to loss of neutrality may include prolonged static positioning, especially sitting, hypermobility especially when participating in extreme sports or dance, and impaired somatosensory input. In the absence of pathology, right stance is a common default stance position. Respiration and gait will reinforce imbalance once neutrality is lost.
