The human spine illustrates a unique design that contributes to its shape and function. Primary and secondary curves provide flexibility, support balance and distribute the body’s weight. At birth, the fetal spine displays a C-shaped curve before growing and developing in response to environmental inputs.
Primary curves include the thoracic and sacral curves. The thoracic curve takes priority during early development. This concavity exists in the upper back and allows space within the chest cavity for internal organs such as the heart and lungs. Near the base of the spine, the sacral curve occurs at birth and provides support for the pelvic organs with its concave structure.
Secondary curves progress in response to gravity and changes in body position from rolling over to walking. As infants toil to hold up their heads, the cervical curve develops and grows toward maturity. This convex curve balances the head’s weight and centralizes its position on top of the spine. The lumbar curve develops in response to gravity, principally, as humans learn to walk. In the lower back, this convexity supports the body during weight-bearing activities.
The intersections found between primary and secondary curves are essential to overall function. These regions support diaphragms which provide structure for the transverse plane of movement (i.e. rotating or twisting). Located at the intersection of the cervical and thoracic curves, the superior thoracic aperture takes the form of a diaphragm. This aperture yields to the passage of nerves and blood vessels communicating between the head and chest cavity. The respiratory diaphragm lives at the union between the thoracic and lumbar curves. This diaphragm provides structure via connections between the ribcage and lumbar vertebrae while supporting optimal lung function. Found at the transition from lumbar and sacral curves, the pelvic floor refers to another diaphragm. The pelvic floor encompasses numerous muscles that protect reproductive organs and support human gait. As humans journey across the landscape, these diaphragms enable the body to move around a vertical axis in space.
Collectively, primary and secondary curves demonstrate the S-shaped appearance of the human spine. Its S-shape allows the human spine to work against gravity in the vertical plane while fostering balance and absorbing shocks during movement. Spinal health depends on the growth and maintenance of these curves with abnormalities or untreated injuries leading to early changes. Dynamic postures become stronger and more efficient with resistance training. With the diaphragms fixed horizontally atop each other, humans maximize postures that foster their physical capacity over the long-term. Body positions, ergonomics and physical activity enhance resiliency while optimizing the quality of life.