The book asks what a movement costs the body, and it counts the answer 3 ways: muscle effort, joint force and the number of parts recruited
Chapter 3 of the Spinal Fitness book states that every movement has a cost and that the body pays it in 3 ways: effort cost, force cost and anatomy cost. Chapter 3 names this question as one of Dr. John Scherger's most important contributions to spinal mechanics: not only whether a movement can be performed, but what it costs.
| Cost | Definition in Chapter 3 | Aligned spine | Poorly aligned spine |
|---|---|---|---|
| Effort cost | The amount of muscular force required to perform and control the movement | Structure reduces unnecessary muscular work | Muscles must work harder just to hold position |
| Force cost | The amount of compression and shear created at the joints | Compression is part of normal function | Excessive compression combined with shear increases tissue stress |
| Anatomy cost | The number of muscles and joints needed to complete and stabilize the task | Accomplishes more with fewer active parts | Recruits more muscles and exposes more joints to control instability |
Chapter 3 states that a mechanically efficient system can accomplish more with fewer active parts, while a mechanically inefficient system recruits more muscles and exposes more joints because it must control instability. The 3 costs are measured on the same movement, so a change in posture changes all 3 at once.
Chapter 6 states that training and rehabilitation have long been built around 1 focus, the muscle providing the force of effort, and it names 3 upgrades from Dr. Scherger's work that current training and treatment technology requires. Each upgrade matches 1 of the 3 costs.
Upgrade 1 is that total effort is not just force of effort. Every successful movement includes the initial muscle effort plus any force required for shear stabilization at the joints. When a movement creates shear, as the book states all third-class lever movements do, the body recruits additional stabilizing effort to stop joint translation, and that effort is part of the mechanical cost. Programs that count only the visible muscle contraction, in the book's words, are ignoring half the equation.
Upgrade 2 is that training must account for all forces created, not just the force of effort. A movement may strengthen the target muscle while creating shear forces that strain the ligaments, discs or facets that stabilize it. The book's example in Chapter 6 is the leg curl, which strengthens the hamstrings while creating anterior shear at the knee that strains the anterior cruciate ligament.
Upgrade 3 is that objective training requires understanding total anatomy, meaning the muscles of effort plus every structure recruited for stabilization. A movement that appears to involve 1 muscle may require bilateral effort muscles, bilateral stabilizing muscles and multiple joint surfaces. The book's summary of the 3 upgrades is a shift from asking what muscle an exercise works to asking what the complete mechanical cost of the movement is and whether the body's stabilizing structures can absorb it.
Chapter 6 describes how poor posture adds to 2 of the costs at the same time. When spinal alignment is poor and the facets cannot provide fixed stabilization against shear, the body recruits muscles to do the work bone should be doing. First, the body generates extra muscular effort to stop joint translation. Second, that same muscular effort drives additional compressive force into the discs and joints. The book states that the body pays twice: once in energy, and once in compression.
Chapter 6 states its Key Principle in 2 sentences: "The safest back is not the back trained to tolerate endless poor-force relationships. The safest back is the back that is not needlessly placed in those relationships in the first place." When the spine has proper structure, force travels through stable joints; when it does not, force travels through compensating muscles.
Chapter 5 restates the 3 costs for force production. Effort cost: the person uses more muscle effort to produce less usable force, which is why an athlete or worker may feel they are working harder than everyone else for the same task. Force cost: poor posture creates more internal force exposure, with more compression and shear accumulating inside the joints. Anatomy cost: poor posture uses more anatomical parts to stabilize the same movement.
The anatomy cost has a count in the book's football contact model in Chapter 5. In poor posture, the model uses 4 muscles and 3 joints for compression and shear, with multifidus bundles running from L2, L3, L4 and L5 to the sacrum. In good posture, it uses 2 muscles and 1 joint for compression, represented at L2-L3. Chapter 5's rule is that more parts means more places to fatigue, more places to fail, and more tissue exposed to compression and shear.
The book's Clinical Insight in Chapter 3 lists 7 signs 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 for training is to identify the mechanical strategy the body is using and then give it a better one, with the coaching message "Your body is not failing. It is compensating. We are going to teach it how to use structure again."
The book's rule for lowering all 3 costs is the one Chapter 3 closes on: restore the curve, shorten the resistance arm, reduce shear. In the 5-step system, the Sit-Up over the PowerCushion and the Pelvic Tilt over a fulcrum are the exercises that load the spine from the anterior direction, where the book states the spine has excellent mechanical advantage.
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 PowerCushion is the fulcrum for the Pelvic Tilt and the Sit-Up, Steps 2 and 3 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.
In the About Dr. Scherger section of my book, I wrote that "he was the first person to show me that the human body operates according to mechanical laws—that it is not random, but governed by principles that can be understood, measured, and improved." Chapter 3 credits him with counting what a movement costs the muscles, the joints and the number of parts recruited.
Our Facebook group is free to join for questions about any of the 5 steps in the Spinal Fitness system.
Effort cost, the muscular force required; force cost, the compression and shear at the joints; and anatomy cost, the number of muscles and joints recruited.
Chapter 6 states that every movement that creates shear requires additional stabilizing effort, so counting only the visible muscle contraction ignores half the equation.
Energy and compression. Muscle doing the work of bone costs extra effort, and that effort drives more compression into the discs and joints.
In the book's football contact model, 4 muscles and 3 joints in poor posture against 2 muscles and 1 joint in good posture.
Restore the curve, shorten the resistance arm, reduce shear, with exercises that load the spine from the anterior direction.
Published October 24, 2026 - Updated October 24, 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
