A lumbar arch held by the fulcrum, a 45-degree start, and an exhale that brings the ribs toward the hips
In Dr. John Scherger's analysis in Eileen Durfee's Spinal Fitness book, a sit-up performed over a supporting fulcrum in proper S-shaped posture takes 170 pounds of muscular effort, produces 1,176 pounds of total compression across 6 lumbar joints, and creates zero shear. The book makes that movement Step 3 of its 5-step system and calls it a curvature-restoration drill, not a fitness sit-up.
The book opens Chapter 14 with its strongest single recommendation: if you only learn one movement from this book, make it the Sit-Up over the PowerCushion. It defines the movement as a curvature-restoration drill that trains the abdominal musculoskeletal complex while protecting the lumbar spine from the shear patterns that flare people up when they try to "just do core." The equipment for all 5 steps is grouped in the spine alignment stretches and exercises collection.
The book lists 4 jobs for Step 3. It restores and reinforces lumbar curvature while the trunk moves against gravity; it builds abdominal strength without teaching the spine to stiffen into a flat, braced posture; it reduces reliance on chronic guarding; and it improves trunk momentum capacity for athletics and real-world tasks. The PowerCushion creates a supportive fulcrum so the trunk can move through a range of motion that encourages a lumbar curve instead of flattening it.
The book then states the structural purpose in 1 paragraph. When the person reclines over the fulcrum, the lumbar spine is placed into a lordotic arch. As the person exhales and sits up, the abdominal muscles contract while the spine moves through a controlled range. At the top of the movement, the lumbar vertebrae are guided toward alignment where compression travels more directly down the spine and shear is minimized. The book's summary of that purpose: the purpose is not to eliminate the lumbar curve, it is to restore and strengthen it.
According to the book, most floor-based sit-ups encourage a posterior pelvic tilt and a flattened lumbar spine. That may build endurance, the book says, but it trains the wrong strategy for someone who already lacks curve. When a sit-up is performed without adequate lumbar support, the movement can create posterior shear at the lower lumbar segments, and the abdominal muscles' force is converted into joint strain and compensatory co-contraction instead of traveling through a stable structure.
The book's mechanism for the supported version: the weight of the upper body creates resistance while the abdominal muscles create effort, and with the lumbar spine supported in its correct structure, those 2 forces combine into a stabilizing resultant force through the lower lumbar joints. When the lumbar curve is supported, the direction of shear shifts from posterior, which the book calls destabilizing, to anterior, where the bony facet contacts absorb it. In that position the external oblique muscles become a primary contributor to lifting the upper body.
Dr. Scherger's model in the book uses the weight of the upper trunk, 100 pounds acting at its center of mass, as the resistance. With proper S-shaped posture, the external oblique provides the initial force of effort at about 1 degree above the positive x-axis. The calculation gives 170 pounds of effort and a resultant of 196 pounds at each joint. Because the direction of that resultant matches the direction of the true effort arm, the vertebral body, the book states that the resultant is stabilized entirely by compression: no shear is created, and no active muscular stabilization is required beyond the initial effort.
| Model (100-lb upper trunk) | Total effort | Total compression | What stabilizes the joints |
|---|---|---|---|
| Proper S-shaped posture over a fulcrum | 170 lb | 1,176 lb across 6 joints | Compression only; total shear zero; 2 muscles (bilateral external obliques) |
| Improper posture, best model | 388 lb | 1,639 lb | Multifidus recruited at every joint |
| Improper posture, worst model | 741 lb | 2,501 lb | Multifidus recruited at every joint |
In improper posture, the book explains, the multifidus must be recruited at every joint to stabilize the shear that bony alignment cannot control, and each multifidus contraction stabilizes some shear while adding more compression. In the book's figures, the best improper model needs 388 pounds of effort, more than twice the 170 pounds of proper posture, and the worst reaches 741 pounds of effort and 2,501 pounds of compression. The book's conclusion: proper posture converts the movement into a first-class lever system requiring only muscular effort and producing only compression, while poor posture requires muscular stabilization at every joint.
The book gives 2 mechanical reasons the PowerCushion makes the sit-up corrective. First, the fulcrum sets the spine to function as if it already possesses proper posture: it imposes the geometry that proper curves would provide, so the muscle angles and lever relationships are correct before the spine has rebuilt them. Second, the fulcrum acts as a fixed external stop that removes the need for third-class shear stabilization during the movement; without it, a sit-up from a flat or reversed-curve spine generates posterior shear that ligaments and deep muscles must hold.
The book's clinical insight on equipment follows from that: attempting the corrective sit-up on a flat surface or with an inappropriately soft support defeats the purpose, because the firmness and diameter of the fulcrum determine the degree of curve imposed. The same chapter's setup rule is to start with the softer option for a stiff, painful, injured or highly guarded spine.
Chapter 14's rule for setup is that you earn it before you count reps, because the setup is what makes the movement corrective instead of provocative. Its 4 non-negotiables:
Execution follows 5 steps. First, start tall: sit upright with the spine tall, a neutral head position and the trunk lightly pressed into the cushion. Inhale and recline until the trunk reaches roughly a 45-degree angle, keeping the neck long and straight. As you inhale, bend the elbows to about 90 degrees and move the upper arms out to expand the ribs. Exhale and drive the chest up and forward, leading with the sternum, with the cue "rib to hip" while the abdominal muscles contract. Return to the upright start of the movement with control, with no flopping and no momentum.
Chapter 14 gives no standalone rep count for Step 3. The 6 to 10 and 10 to 15 rep figures in the next section belong to the book's Desk, Driver and Warehouse Standards.
The range rule limits the recline: go back only as far as you can without extending or arching the neck or tilting the head back, and early on that may be only an inch or two, which the book calls correct. The neck rule is that the neck stays straight and neutral throughout, with no looking back, no chin tuck and no head leading the movement; the chapter summary calls neck neutral non-negotiable. Because most beginners lack the cervical endurance to hold the head in neutral, the trainer first supports the weight of the head, and after initial training a soft cervical collar may be used temporarily while the neck muscles strengthen.
In the book's correction loop, the Sit-Up is the center of Phase 3, Structural Rebuild, after Decompression (Back Trac rolling) and Load Correction (Pelvic Tilt). The book describes Phase 3 as restoring the spinal curves while the trunk moves against gravity and resistance, retraining the anterior support system without flattening the lumbar spine or letting the neck and hip flexors dominate. The trainer rule for the loop: if a client is still bracing through Step 1, Step 2 or Step 4, they are not ready for more load.
| Book standard | When | Sit-Up dose |
|---|---|---|
| Desk Standard | Mid-shift reset, 3 to 5 minutes | 6 to 10 reps, light density, plus 1 to 2 minutes of Back Trac rolling |
| Driver Standard | Post-shift, 10 to 20 minutes | 6 to 10 reps |
| Warehouse Standard | Pre-shift, 5 to 8 minutes | 6 to 10 reps, light density |
| Warehouse Standard | Post-shift, 15 to 20 minutes | 10 to 15 reps |
In the Desk Standard, that 3-to-5-minute reset comes mid-shift, after a 2-to-4-minute Neck Flexion prime of 6 reps and alongside micro-breaks of 10 to 30 seconds every 45 to 60 minutes. Track B in the book, for high-exposure workers at 10 to 20 minutes per day, adds progressive Sit-Up range and density. Track C, recovery and return-to-work, starts the spine on the softest fulcrum and minimal range, and gates progress by form and comfort rather than by schedule. The book's Progression Rule applies to reps, range and density alike: progress only when the current dose no longer produces the intended strain, or when the person shows cleaner form with less compensation than in the previous session.
The book's universal rules govern every rep: strain is acceptable and pain is not, every rep is controlled because fast reps recruit compensation, and neutral spinal alignment comes before effort. When a screen returns mostly red results with high muscle tone, swelling or severe guarding, the book starts with Step 5 only and holds off the Sit-Up until irritability has reduced to moderate or lower.
New numbness or tingling, radiating symptoms, weakness, bowel or bladder changes, or sharp escalating pain: pause training and escalate to medical evaluation. The book also states that fused spinal segments, natural or surgical, cannot be reshaped.
The Power Cushion is listed at Creatrix as coming soon, in soft (blue) and medium (orange) densities; the book's starting rule is the softer option for a stiff or guarded spine.
Practitioner Eileen Durfee, NBS (Nutritional Balancing Science), NASM-CPT — wellness educator, inventor, author, and a Nationally Certified Spinal Fitness Specialist.
Chapter 14 of my book opens with a single recommendation: make the Sit-Up over the PowerCushion the 1 movement you learn from the book. Since 2010 I have worked in the wellness industry, earning Nutritional Balancing Science training and becoming a NASM Certified Personal Trainer.
The photographs in Chapter 14 show me coaching Nick Diaz through the Step 3 Sit-Up over the PowerCushion and demonstrating the advanced loaded variation. Our Facebook group is free to join for questions about Step 3 or any of the 5 steps.
The book states that most floor sit-ups encourage a posterior pelvic tilt and a flattened lumbar spine. Over the PowerCushion, the lumbar spine is held in a lordotic arch, and the book's model gives 170 lb of effort with zero shear in proper posture.
Start at about 45 degrees and recline only as far as you can without arching the neck or tilting the head back. The book says early on that may be only an inch or two.
The book says start with the softer option for stiff, painful, injured or highly guarded spines. It also says the firmness and diameter of the fulcrum determine the degree of curve imposed.
The book's workplace standards use 6 to 10 reps at light density for a mid-shift reset and 10 to 15 reps in the Warehouse Standard post-shift session. Progress only when the current dose no longer produces the intended strain.
The book says most beginners lack the cervical endurance to hold the head in neutral. A trainer supports the head first, and a soft cervical collar may be used temporarily while the neck muscles strengthen.
Published October 8, 2026 • Updated October 8, 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
This article is for educational purposes only. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease. Nuco Enterprise Solutions LLC.
