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.

What Is the Spinal Flexion Strength Test?

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.

What Is the Muscle Meter?

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.

Recommended Standard Setup

For consistency and safety, the preferred standard protocol is a seated isometric trunk flexion test.

Client position

• 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

Why seated?

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.

Option 1: Spinal Flexion Test With Pusher Cap

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.

Step-by-Step Protocol / Practice

1. Prepare the client

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.

2. Set the client position

• Client seated upright

• Feet flat

• Hips and knees around 90 degrees

• Pelvis stabilised

• Arms crossed or standardised

• Trunk neutral before testing

3. Place the device

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.

4. Stabilise the position

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.

5. Give clear instructions

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.”

6. Record trials

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

7. Identify invalid trials

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

Option 2: Spinal Flexion Test With Puller Straps

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.

Step-by-Step Protocol / Practice

1. Prepare the client

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.”

2. Set the client position

• 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

3. Place the strap

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

4. Stabilise the position

Stabilise:

• Pelvis

• Thighs

• Feet

• Trunk start position

Prevent:

• Arm pulling

• Feet lifting

• Pelvic shift

• Trunk rotation

• Excess hip flexion

5. Give clear instructions

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.”

6. Record trials

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

7. Identify invalid trials

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

Scoring

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

Understanding the Result

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, Norms and Comparative Data

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.

Assessing and Providing Context for Different Client Populations

Youth clients

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.

Adults and general fitness clients

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.

Older adults

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.

Athletes and sport clients

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.

Workplace and manual task clients

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.

Clients returning after injury

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.

Clients with pain or persistent 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.

Higher body mass clients

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.

Reliability and Measurement Considerations

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 and Limitations

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.

Practical Applications

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.

Ideas to Make the Result Better

If trunk flexion force is low

Consider assessing general trunk strength, hip strength, confidence with trunk loading, pain response, breathing and bracing strategy, and functional lifting or carrying tolerance.

If flexion is much lower than extension

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.

If pain limits the result

Consider reducing intensity, using submaximal monitoring, recording pain response clearly, testing a less provocative position and referring on if symptoms fall outside professional scope.

If force is good but function is limited

Consider whether the limiting factor is endurance, coordination, movement confidence, range of motion, hip strength, technique, fatigue response or sport/work-specific task tolerance.

If the client is improving

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.

Safety Considerations

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.

Recommended Standard Protocol Summary

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

FAQs

What does this test measure?

It measures isometric trunk flexion force in a specific testing setup.

What does the Muscle Meter measure by itself?

When used on its own, the Muscle Meter primarily measures peak force.

Can this test diagnose back pain?

No. It may provide useful information about force output, but it does not diagnose the cause of pain.

Should I use the pusher cap or puller straps?

Use the pusher cap for a quick, simple setup. Use puller straps when you want stronger fixation or when testing stronger clients.

Can I compare pusher cap and puller strap results?

Not directly. They should be treated as different protocols unless the setup has been validated for comparison.

Are there Muscle Meter-specific norms?

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.

What is the main metric?

Peak force is usually the main metric. Torque may be useful if lever arm is measured.

Key Takeaways

• 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.

References

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