The Spinal Flexion Strength Test measures how much force a client can produce when flexing the trunk forward against a Muscle Meter, handheld dynamometer or fixed resistance setup.
This test can be performed using either:
The pusher cap, where the client pushes forward directly into the Muscle Meter
The puller straps, where the client pulls forward against a strap system with the Muscle Meter in-line
Trunk flexion strength may be relevant for lifting, carrying, bracing, sport, occupational tasks, trunk control, gym-based exercise and general physical capacity.
The result should not be used alone to diagnose back pain, spinal pathology, tissue injury or readiness for sport or work. It should be interpreted alongside symptoms, confidence, range of motion, movement quality, work or sport demands, training history and related assessment findings.
The Spinal Flexion Strength Test is an isometric trunk strength assessment.
The client attempts to bend the trunk forward while the Muscle Meter or strap setup resists movement. The aim is to measure force output without allowing the trunk to move through range.
The test does not measure spinal mobility, pain cause, spinal stability, lifting technique, endurance or functional capacity on its own.
It is most useful when the same setup is repeated over time so results can be compared with the client’s own baseline.
The Muscle Meter is a handheld dynamometry tool used to measure force output during push, pull and isometric strength assessments.
When used on its own, the Muscle Meter primarily measures peak force, which is the highest force value produced during the test.
When used with Measurz, Muscle Meter data can be recorded and analysed with a broader set of strength and force-time metrics, including:
Peak force
Impulse
Torque
Rate of torque development
Rate of force development
Time to peak
Fatigue index
For routine spinal flexion testing, peak force is usually the main metric.
Other metrics may be useful when the setup supports them:
Torque may be useful if the lever arm from the trunk axis to the force application point is measured.
Rate of force development may be useful for athletes, manual workers or clients who need rapid trunk force production.
Time to peak may help show whether force is produced quickly or slowly.
Impulse may be useful if sustained trunk flexion force over a defined time window is relevant.
Fatigue index is only relevant if repeated or sustained contractions are tested.
Not every test needs every metric. The metric should match the assessment question.
For consistency and safety, the preferred standard protocol is a seated isometric trunk flexion test.
Client seated upright on a stable bench, chair or plinth
Feet flat on the floor
Hips flexed to approximately 90 degrees
Knees flexed to approximately 90 degrees
Pelvis neutral
Trunk upright
Arms crossed over chest or placed in a standardised position
Head and neck neutral
Feet, pelvis and thighs stabilised where possible
A seated position helps reduce lower-limb contribution and makes it easier to standardise:
Pelvis position
Trunk angle
Foot position
Hip and knee angle
Device placement
Retesting conditions
A standing version may be used for sport or workplace specificity, but seated testing is usually easier to repeat.
The pusher cap protocol is used when the client pushes forward directly into the Muscle Meter while the professional or an external setup stabilises the device.
This option is simple and fast. However, it relies more on the professional’s ability to resist force. For stronger clients, a fixed setup or puller strap protocol may provide better repeatability.
Explain the test:
“We are going to measure how much force you can produce when pushing your trunk forward into the Muscle Meter. Build your effort gradually, push as hard as you safely can, and tell me if you feel pain or unusual symptoms.”
Record current symptoms, confidence, recent flare-ups, fatigue and any movements that should be avoided.
Client seated upright
Feet flat
Hips and knees around 90 degrees
Pelvis stabilised
Arms crossed or standardised
Trunk neutral before testing
Place the pusher cap against the upper sternum or central upper chest, depending on client comfort and the chosen protocol.
Avoid placing direct pressure over painful or sensitive areas.
Record the exact contact point so the same position can be repeated.
Stabilise the client so that force comes mainly from trunk flexion.
Control:
Pelvis movement
Hip flexion strategy
Feet lifting
Arm pushing
Trunk rotation
Shoulder protraction compensation
Where possible, use a belt, straps, stable chair or assistant support to minimise pelvis and lower-limb movement.
Use consistent cueing:
“Push your chest forward into the Muscle Meter. Build up gradually. Push as hard as you safely can. Hold. Keep breathing. Do not lift your feet or push with your arms.”
Use:
1–2 submaximal practice trials
2–3 recorded maximal trials
3–5 second contraction
45–90 seconds rest between trials
Same scoring method each time: best score or average score
Repeat or mark invalid if:
Feet lift
Pelvis shifts
Client pushes with arms
Trunk rotates
Device slips
Client loses position
Pain unexpectedly limits effort
Professional cannot stabilise the device
The puller strap protocol uses the Muscle Meter with straps, handles or a fixed anchor point to measure force while the client pulls into trunk flexion.
This setup may be more repeatable for stronger clients because it reduces the influence of the professional’s ability to manually resist force.
Explain the test:
“We are going to measure how much force you can produce when pulling your trunk forward against the straps. Build your effort gradually, pull as hard as you safely can, and tell me if you feel pain or unusual symptoms.”
Client seated upright
Feet flat
Hips and knees around 90 degrees
Pelvis stabilised
Trunk neutral
Strap positioned across the upper chest or attached to a chest harness/strap system
Muscle Meter connected in-line with the strap and anchor point
Place the strap across the upper chest/sternum region, depending on comfort and setup.
The strap should allow the client to attempt trunk flexion without using the arms to pull.
Avoid high strap placement around the neck.
Record:
Strap position
Anchor height
Anchor distance
Client distance from anchor
Muscle Meter orientation
Stabilise:
Pelvis
Thighs
Feet
Trunk start position
Prevent:
Arm pulling
Feet lifting
Pelvic shift
Trunk rotation
Excess hip flexion
Use consistent cueing:
“Pull your trunk forward into the strap. Build up gradually. Pull as hard as you safely can. Hold. Keep breathing. Keep your hips and feet still.”
Use:
1–2 submaximal practice trials
2–3 recorded maximal trials
3–5 second contraction
45–90 seconds rest
Best or average score recorded consistently
Repeat or mark invalid if:
Strap slips
Client pulls with arms
Pelvis moves
Feet lift
Trunk rotates
Anchor point shifts
Muscle Meter angle changes
Pain unexpectedly limits effort
The primary score is usually peak force.
Record whether the final value is:
Best trial
Average of trials
Peak force
Force normalised to body mass, if used
Torque, if lever arm is measured
Use the same scoring method at retest.
Do not compare:
Pusher cap values with puller strap values as if they are the same test
Seated values with standing values as if they are the same test
Results from different anchor heights, strap positions or device placements
A higher score may suggest greater trunk flexion force output in that specific test setup.
A lower score may suggest reduced trunk flexion force output, but the reason should be interpreted carefully.
Possible influences include:
Pain
Apprehension
Poor familiarisation
Fatigue
Guarding
Poor stabilisation
Pelvis movement
Hip compensation
Different device placement
Different strap angle
Different trunk position
Breath holding
Client confidence
The result becomes more useful when compared with:
The client’s own baseline
Repeated measurements over time
Extension strength using the same setup
Symptoms
Confidence
Range of motion
Lifting or sport demands
Work demands
Related hip and trunk strength tests
Functional or performance tasks
A single score should not be used alone to explain pain, determine capacity or clear participation.
Published reference values for the exact Muscle Meter spinal flexion pusher-cap or puller-strap protocol are currently limited. The best available data should be used as comparison context, not direct Muscle Meter norms.
The easiest way to understand trunk strength data is to look at torque relative to body mass, usually reported as N·m/kg. This adjusts strength for body size and can be easier to compare between clients.
In healthy adults aged 18–30 years, ÜNver et al. (2024) reported the following approximate trunk flexion values using an isokinetic dynamometer:
Men: trunk flexion was approximately 2.9 N·m/kg
Women: trunk flexion was approximately 1.7 N·m/kg
Combined group: trunk flexion was approximately 2.2 N·m/kg
These values were collected with a different device and protocol, so they should not be treated as exact Muscle Meter targets. They are useful as broad context for understanding trunk flexion strength in healthy young adults.
For Muscle Meter testing, the best comparison is usually:
The client’s own baseline
Their repeated results over time
Flexion compared with extension using the same setup
Symptoms during testing
Confidence and effort quality
Work, sport or training demands
Use published values as educational context, not as a pass/fail standard.
In youth clients, trunk flexion strength may be influenced by growth, maturation, coordination, attention, training age and confidence with maximal effort testing.
Use the test mainly for baseline comparison, progress tracking and sport or movement education.
Avoid comparing youth clients directly with adult reference values unless the research population matches their age and maturation stage.
For general fitness clients, this test is often most useful for showing whether trunk flexion force output is changing over time.
Use the result to provide context around baseline strength, confidence with trunk loading, symptoms during resisted trunk effort and functional goals such as lifting, carrying or gym-based exercise.
In older adults, trunk flexion strength may be relevant to transfers, lifting, carrying, walking confidence and daily tasks.
Use clear instructions, allow practice trials, monitor fatigue and consider longer rest periods. Interpret the result alongside balance, gait, sit-to-stand ability, hip strength, confidence and daily function.
For athletes, trunk flexion strength may provide useful context for bracing, contact demands, sprinting, jumping, grappling, throwing, kicking or lifting.
Peak trunk flexion force alone does not equal performance. Interpret results with rate of force development, trunk rotation strength, hip strength, sport skill, fatigue resistance and role demands.
For workplace or occupational settings, trunk flexion strength may provide context for lifting, carrying, pushing, pulling, bracing and repeated manual tasks.
Do not use one trunk flexion score to clear someone for full work duties. Interpret with job demands, symptoms, fatigue, ergonomics, confidence and task-specific tolerance.
For clients returning after back, hip, pelvic or lower-limb injury, trunk flexion strength testing may help monitor force output, confidence and symptom response.
A stronger score does not confirm readiness. A lower score does not explain the cause of symptoms.
Pain, fear of movement, guarding, fatigue, apprehension and low confidence can all reduce trunk flexion force output.
Start with lower intensity if needed, record symptoms before and after, and avoid maximal testing if symptoms are highly irritable.
In higher body mass clients, absolute force may be high, but force relative to body mass may provide different context.
Avoid assuming that higher body mass automatically means poor trunk capacity. Interpretation should be linked to the client’s goals and tasks.
Handheld dynamometry can be reliable for trunk flexion testing when the setup is controlled. Althobaiti and Falla (2023) reported that handheld dynamometry demonstrated acceptable reliability and criterion validity for measuring trunk muscle strength in people with and without chronic non-specific low back pain. De Blaiser et al. (2018) also reported that handheld dynamometry could be reliable and valid for measuring trunk flexor and extensor strength in a healthy athletic population.
To improve reliability:
Use the same test position each time.
Use the same device attachment each time.
Standardise pusher cap or strap placement.
Standardise anchor height and distance if using straps.
Stabilise the pelvis and lower body.
Use consistent instructions.
Use the same contraction duration.
Use the same rest period.
Record symptoms and compensations.
Avoid comparing different protocols directly.
A change is more meaningful when it is repeated across sessions, aligns with improved symptoms, confidence or function, and is supported by related assessment findings.
Common errors include:
Poor pelvis stabilisation
Hip movement replacing trunk flexion
Arm pushing or pulling during flexion
Trunk rotation during testing
Inconsistent device placement
Inconsistent strap angle
Anchor point movement
Feet lifting
Breath holding
Testing through high pain
Comparing pusher cap and strap results directly
Treating the score as a diagnosis
Limitations include:
Trunk flexion testing is highly setup-dependent.
Manual resistance may be limited by the professional’s strength.
Strap setup requires careful anchor control.
Pain, fear or guarding can reduce force output.
Peak force does not measure endurance or movement quality.
Published norms are not universal across protocols.
This protocol may be useful for:
Baseline trunk flexion strength assessment
Monitoring progress over time
Comparing trunk flexion and extension capacity
Strength profiling for sport or occupational demands
Tracking change during training or intervention blocks
Client education
Identifying whether force output changes alongside symptoms or function
It may be especially useful when combined with spine range of motion, hip strength testing, functional lifting tasks, pain monitoring and work or sport-specific capacity assessments.
Consider assessing general trunk strength, hip strength, confidence with trunk loading, pain response, breathing and bracing strategy, and functional lifting or carrying tolerance.
Consider comparing with trunk flexion confidence, abdominal strength tasks, hip flexor contribution, pain with forward bending and lifting or sit-up style tasks where appropriate.
Do not assume the cause from the score alone.
Consider reducing intensity, using submaximal monitoring, recording pain response clearly, testing a less provocative position and referring on if symptoms fall outside professional scope.
Consider whether the limiting factor is endurance, coordination, movement confidence, range of motion, hip strength, technique, fatigue response or sport/work-specific task tolerance.
Useful signs may include higher peak force, lower pain at the same force output, better confidence, fewer compensations and improved functional or work-task tolerance.
Avoid maximal testing or modify the protocol if the client reports:
Severe or worsening back pain
Sharp pain during setup
Neurological symptoms
Dizziness
Recent spinal surgery
Recent trauma
Unexplained symptoms
Symptoms outside your professional scope
Stop testing if symptoms become sharp, worsening, unusual or unsafe.
For most professional settings, use this as the default:
Position: seated
Trunk start position: neutral
Hip and knee angle: approximately 90 degrees
Trials: 2–3 recorded trials
Contraction duration: 3–5 seconds
Rest: 45–90 seconds
Metric: peak force
Attachment: pusher cap or puller straps, recorded clearly
Final score: best trial or average trial, used consistently
Key requirement: same setup at retest
It measures isometric trunk flexion force in a specific testing setup.
When used on its own, the Muscle Meter primarily measures peak force.
No. It may provide useful information about force output, but it does not diagnose the cause of pain.
Use the pusher cap for a quick, simple setup. Use puller straps when you want stronger fixation or when testing stronger clients.
Not directly. They should be treated as different protocols unless the setup has been validated for comparison.
Published direct Muscle Meter norms for this exact protocol are limited. Use the client’s baseline first, and use published trunk dynamometry data as broader comparison context.
Peak force is usually the main metric. Torque may be useful if lever arm is measured.
The Muscle Meter can be used to assess spinal flexion strength with either the pusher cap or puller straps.
The pusher cap is simple and practical, but may be limited by the professional’s ability to resist force.
Puller straps may improve consistency for stronger clients when the anchor setup is stable.
Peak force is usually the main metric.
Strap-based and pusher-cap results should be recorded as separate protocols.
Published trunk flexion values are useful as comparison data, not direct Muscle Meter norms.
Results are most useful when compared with the client’s own baseline and repeated over time.
The test should support assessment reasoning, not diagnosis or clearance decisions.
Althobaiti, S., & Falla, D. (2023). Reliability and criterion validity of handheld dynamometry for measuring trunk muscle strength in people with and without chronic non-specific low back pain. Musculoskeletal Science and Practice, 66, Article 102799. https://doi.org/10.1016/j.msksp.2023.102799
De Blaiser, C., De Ridder, R., Willems, T., Danneels, L., & Roosen, P. (2018). Reliability and validity of trunk flexor and trunk extensor strength measurements using handheld dynamometry in a healthy athletic population. Physical Therapy in Sport, 34, 180–186. https://doi.org/10.1016/j.ptsp.2018.10.005
ÜNver, F., Gur Kabul, E., Buke, M., & ÜNver, B. (2024). Trunk flexor and extensor muscle strength capacity in healthy individuals. Turkish Journal of Sports Medicine, 59(3), 112–118. https://doi.org/10.47447/tjsm.0827
