Two workers on the same job can pay different physical costs, and the book traces the difference to structure rather than conditioning
Chapters 2 and 3 of the Spinal Fitness book describe the fatigue gap: 2 workers start the same shift, and the one with proper spinal structure spends less energy every hour while the one without it spends more. The book's reframe is that "Fatigue is not always a conditioning problem. Sometimes it is a structural cost problem."
Chapter 3 translates Dr. John Scherger's work into 1 guiding formula: Ideal Shape = Efficient Energy Expenditure + Effective Momentum. When the spine has its proper S-shaped structure, the body spends less energy managing gravity and can produce more useful force output. When the shape is lost, both sides of the formula suffer: energy expenditure increases because the muscles must work harder to keep the body upright, and effective momentum decreases because force is no longer transferred cleanly through the structure.
The book draws 1 conclusion from that formula. A person with poor spinal structure may feel tired before the real work begins, because the body has already been working all day to hold itself together. That is the basis for its statement that fatigue is sometimes a structural cost problem rather than a conditioning problem.
Chapter 3 states that muscles produce force best when they work near an optimal length, and that poor posture changes those lengths. Forward head posture shortens some posterior neck muscles while forcing other stabilizers to work from a disadvantaged position. A rounded trunk lengthens and overloads parts of the posterior chain muscles. A tucked pelvis changes hamstring muscle tension and reduces the ability of the hips to extend fully.
Chapter 6 lists the length-tension changes region by region:
| Posture change | Length-tension effect the book lists |
|---|---|
| Forward head posture | Cervical extensors and upper traps become tonic and short; deep neck flexors often lose endurance and coordination |
| Rounded shoulders | Pectorals shorten; scapular retractors and lower traps lose their efficient length and timing |
| Flattened lumbar curve | Hamstrings and the posterior chain become tonic; the trunk loses stable leverage |
| Global effect | More co-contraction, less efficient movement, faster fatigue |
The Chapter 6 summary adds the rule that tight muscles are often tonic from compensation, not strong from training. At the beginning of the day the body may compensate well enough; by the end of the day, Chapter 3 states, the cost has accumulated and the person feels tighter, heavier, slower and less coordinated.
Chapter 3 states that poor posture creates expense before movement begins. When the trunk mass shifts forward of the hips, the hamstrings and spinal extensors must work to keep the body from tipping farther forward. When the head shifts forward, the posterior neck muscles take on that work. When the ribs collapse and the pelvis tucks, the diaphragm, hip flexors, lumbar stabilizers and thoracic spine all lose mechanical freedom.
The book lists the result in 4 settings: the worker begins the lift already braced, the athlete begins the sprint already tight, the driver begins the route already in compensation, and the desk worker begins the day already draining cervical and thoracic endurance. Its line for the desk case is "Sitting in poor posture is not doing nothing. It is sustained mechanical work in a poor leverage position."
Chapter 2 credits Dr. Scherger's research with the pattern: it appeared in elite athletes and appears in warehouses, delivery routes and office work. Chapter 3 describes the 2 workers: the one with proper spinal structure still gets tired, but fatigue rises more slowly because the structure carries more of the load, and the one with poor spinal structure must use more muscular effort to sit, stand, lift, push, drive or recover. By mid-shift that worker is tighter, by the end of the day guarded, and after months or years the body may begin to break down.
Chapter 2 gives the lever reason. The person with proper spinal curves generates force through first-class lever systems and can lean forward into greater mechanical advantage under load. The person without those curves must stay more upright in posture to keep what stability they have, cannot generate the same momentum, and relies more on muscular bracing every hour. Chapter 2 adds that the most injured workers are often the most experienced, the ones who have been compensating longest.
Chapter 2 also names the modern exposure profile that produces the gap without any lifting: prolonged sitting, prolonged driving, sustained screen focus, and posture held under fatigue. Its sequence for that day is that the neck drifts forward, the shoulders round, the thoracic spine stiffens, and the low back either flattens or hyperextends to compensate.
Chapter 3 writes the cycle as 6 links: lost curve, increased shear, muscle guarding, fatigue, more collapse, more guarding. The book states that the nervous system tightens tissues to create stability when structure is missing, which is why poor posture often feels like tightness, and that the protection helps in the short term but becomes expensive over time.
The book's Clinical Insight in Chapter 3 lists 7 clues that the body is paying more to manage gravity: forward head posture, rib flare, chronic hamstring gripping, tucked pelvis, flat low back, excessive lumbar extension and constant shoulder elevation. Its instruction is that the solution is not simply to stretch what feels tight, but to restore the curves and teach the body to hold them under real-life doses of gravity.
Chapter 7's desk template names the high-leverage interventions for screen teams as cervical micro-dose training, seated posture resets and regular breaks to restore the lumbar curve. Chapter 9 sets the time: Track A, basic prevention for all staff, is a daily micro-dose of 5 to 10 minutes total covering cervical micro-dose, lumbar curve reset and end-of-shift decompression; Track B, for high exposure, is 10 to 20 minutes per day and adds the Pelvic Tilt with resistance, progressive Sit-Up range and density, and guided Back Trac rolling.
Chapter 6 states the reason the neck comes first in that dose: small changes in head position create very large changes in the forces a body must manage across a shift, which makes cervical training one of the highest-leverage interventions in the system.
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 Neck Shaper carries Step 4, Neck Flexion, and the Back Trac roller is Step 1 of the 5-step system.
Practitioner Eileen Durfee, NBS (Nutritional Balancing Science), NASM-CPT - wellness educator, inventor, author, and a Nationally Certified Spinal Fitness Specialist.
On long sitting days I stand up at every bathroom, food or water break and do neck flexion with the Neck Shaper, about 10 reps each time. Chapter 7 of my book lists cervical micro-dose training as a high-leverage intervention for desk and screen teams.
Our Facebook group is free to join for questions about any of the 5 steps in the Spinal Fitness system.
The book's term for 2 workers doing the same job at different physical cost: the worker with proper spinal structure spends less energy every hour, and the gap widens as the shift goes on.
The book states that sitting in poor posture is sustained mechanical work in a poor leverage position, so the muscles spend energy holding the body up before any task begins.
No. Chapter 6 states that tight muscles are often tonic from compensation, not strong from training.
The book states that the solution is not simply to stretch what feels tight, but to restore the curves and teach the body to hold them under gravity.
Track A is 5 to 10 minutes total per day; Track B, for high-exposure roles, is 10 to 20 minutes per day.
Published October 22, 2026 - Updated October 22, 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
