Human life begins in flexion, develops toward an upright S-shape, and often drifts back toward a flexed C-shape, and the book reads that drift as mechanical
Chapter 3 of the Spinal Fitness book calls it the lifespan arc: C-shape, then S-shape, then a drift toward the C-shape again with age, accumulated strain, injury and loss of curve integrity. The book's position is that "That drift is common, but it should not be accepted as inevitable," and Chapter 5 lists what the drift costs: the ability to get out of a chair, climb stairs, catch balance and recover from a stumble.
Chapter 3 uses the riddle of the Sphinx to set out the pattern: a creature that walks on 4 legs in the morning, 2 legs at noon and 3 legs in the evening, the human being crawling as a baby, walking upright as an adult, and leaning on a cane in older age. Chapter 3 reads the riddle as a spinal pattern. Human life begins in flexion, develops toward the upright S-shaped structure, and often drifts back toward a flexed C-shaped posture.
Chapter 2 lists the inputs that pull the spine back toward that flexed pattern as accumulated strain, reduced movement, poor posture, injury history and loss of curve integrity, and states that this is why many older adults become more rounded, stiff and forward-bent over time. Chapter 3 states the purpose of Spinal Fitness for the arc in 2 sentences: "Aging does not have to mean surrendering structure. But structure must be maintained."
Chapter 5 credits Dr. John Scherger with identifying 2 physical abilities made possible by the human S-shaped spine. Effective mobility is the ability to stand upright and move through space on 2 legs: walking, running, striding and changing direction. Effective momentum, ability 2, is the ability to move the trunk forward against a resistance force while the spine becomes more stable.
The book compares 3 spinal patterns. Quadrupeds use a C-shaped spine that works for 4-legged support but does not walk efficiently upright on 2 legs or generate anterior trunk momentum the way humans do. Apes can briefly walk upright, often with bent knees and constant hamstring muscle effort. The human S-shaped spine provides both abilities, and the book's conclusion is that preserving the S-shape means preserving access to those abilities, while losing it means losing both.
Effective mobility depends on 1 condition: the upper trunk balanced over the hip joints. With the trunk stacked, Scherger's walking analysis in Chapter 5 shows the planted leg's hamstring needing essentially zero effort for postural maintenance; with the upper trunk forward, the same hamstring must generate substantial effort to keep the body upright, and the book lists the aging adult's loss as confidence in balance.
Chapter 5 states that as people lose spinal curves, they often lose the ability to move confidently into the world: they shorten their stride, bend forward, brace through the hips and hamstrings, and avoid tasks that require forward drive. The book's phrase is that the loss is not only posture but capability. It lists 7 tasks that require force transfer:
When the spine drifts toward a C-shape, the book states, the person loses both effective mobility and effective momentum, and the body becomes more cautious because it has less structural confidence. Chapter 5's translation for older adults is that preserving effective momentum helps keep the ability to get up, move forward, recover balance and stay independent.
Chapter 2 explains the lever reason the S-shape matters for getting up. A quadruped rises from the prone position, belly toward the ground, with 4 limbs pressing into a supporting base. The human body must be able to rise from the supine position, on the back, which the book describes as a very different lever system: the body must curl upward against gravity, organize the pelvis and spine, and bring the trunk upright. The 2 lordotic curves create the lever relationships that make this efficient and direct the force into compression-dominant patterns instead of uncontrolled shear.
Without those curves, Chapter 2 states, the movement becomes mechanically expensive: the body must recruit more muscles, stabilize more joints and control more shear before it completes the task. Chapter 2 lists rising from the floor first among the 6 movement patterns that define human capability.
Chapter 2 names the daily answer to the drift spinal hygiene: the practice of preserving the curves, maintaining movement and reducing the compensation patterns that accelerate decline. Chapter 2 assigns spinal hygiene a purpose at 5 stages of life: for children it supports development, for adults it preserves function, for workers it reduces exposure risk, for athletes it protects the structure that produces performance, and for older adults it helps resist the gradual drift toward flexion, stiffness and loss of independence.
The book's translations for older adults carry the same rule into the neck and the whole spine. Chapter 3: Spinal Fitness helps preserve the curves that support movement, balance and independence. Chapter 4: preserving the neck curve helps protect motion and reduce the forward drift that steals independence.
Chapter 9 carries 1 caution for spines that have changed with age: if parts of the spine are naturally fused or surgically fused, those fused segments cannot be reshaped. The program focuses on 3 aims: optimizing what can change, improving force management, and protecting the adjacent spinal segments above and below the fusion.
Pain, numbness, tingling and dizziness are the stop signs in the Spinal Fitness book. When one appears, stop the exercise, get evaluated, and then proceed with a therapeutic exercise program designed by a Spinal Fitness expert. The book's training rule for every step is that strain is acceptable and pain is not.
The Back Trac roller is Step 1 of the 5-step system, and the Neck Shaper carries Step 4, Neck Flexion.
Practitioner Eileen Durfee, NBS (Nutritional Balancing Science), NASM-CPT - wellness educator, inventor, author, and a Nationally Certified Spinal Fitness Specialist.
The About the Author page of the Spinal Fitness book states: "At an age when many people expect decline, Eileen feels stronger, healthier, and more vibrant than she did in her twenties." Her own bone density is normal and has been all along, and jumping is one of the activities she recommends.
Our Facebook group is free to join for questions about any of the 5 steps in the Spinal Fitness system.
The book's name for the pattern C-shape in infancy, S-shape in adulthood, and a drift back toward a flexed C-shape with age, strain, injury and loss of curve integrity.
The book states: "That drift is common, but it should not be accepted as inevitable."
Getting out of a chair, climbing stairs, catching balance, pushing open a heavy door, carrying groceries, walking uphill and recovering from a stumble.
The book states that rising from the supine position is a different lever system from rising off the stomach, and the lordotic curves make it efficient.
No. Chapter 9 states that fused segments cannot be reshaped, and the program protects the segments above and below them.
Published October 30, 2026 - Updated October 30, 2026
By Eileen Durfee, Nationally Certified Spinal Fitness Specialist, NASM-CPT, and author of the Spinal Fitness book.
More from Eileen Durfee
Eileen's free guide, Is Your Posture Aging You?, on EileenDurfee.com
