The Spinal Lateral Flexion Strength Test measures how much force a client can produce when bending the trunk sideways against a Muscle Meter, handheld dynamometer or fixed resistance setup.
This assessment can be performed using either:
the Pusher Cap, where the client pushes sideways directly into the Muscle Meter
the Puller Straps, where the client pulls sideways against a fixed strap system with the Muscle Meter positioned in-line
Trunk lateral flexion strength contributes to postural control, carrying tasks, lifting, change of direction, walking, running, overhead activities, manual work and many sporting movements. The lateral trunk muscles also play an important role in controlling side-to-side movement of the spine and pelvis during everyday function.
The result should not be used alone to diagnose low back pain, spinal pathology, rib dysfunction or readiness to return to work or sport. It should always be interpreted alongside symptoms, confidence, range of motion, movement quality, work or sporting demands and related assessment findings.
The Spinal Lateral Flexion Strength Test is an isometric trunk strength assessment.
The client attempts to bend the trunk sideways while the Muscle Meter or strap system resists movement. The objective is to measure lateral trunk force production without allowing visible trunk movement.
The assessment does not directly measure:
spinal mobility
movement quality
balance
endurance
pain source
functional capacity
It is most valuable when repeated under identical conditions so results can be compared with the client's previous assessments.
The Muscle Meter is a handheld dynamometry device designed to objectively measure force during push, pull and isometric strength assessments.
When used independently, the Muscle Meter primarily measures peak force, representing the highest force produced during the assessment.
When connected with Measurz, additional force-time metrics can also be analysed, including:
Peak Force
Force Relative to Body Weight
Impulse
Torque
Rate of Force Development
Rate of Torque Development
Time to Peak
Fatigue Index
For routine spinal lateral flexion testing, peak force is generally the primary outcome measure.
Additional metrics may be useful depending on the assessment objective:
Torque when the lever arm is measured.
Rate of Force Development for athletes or occupations requiring rapid trunk stabilisation.
Time to Peak to evaluate how quickly force is generated.
Impulse when sustained contractions are being assessed.
Fatigue Index during repeated or prolonged contractions.
Not every assessment requires every metric. The selected metric should answer the assessment question.
For consistency and repeatability, a seated isometric protocol is recommended.
Seated upright on a stable chair or plinth
Feet flat on the floor
Hips flexed to approximately 90°
Knees flexed to approximately 90°
Pelvis neutral
Trunk upright
Arms crossed over the chest
Head facing forwards
A seated position reduces lower-limb contribution and allows consistent standardisation of:
pelvic position
trunk position
hip angle
knee angle
foot placement
device placement
Standing protocols may be appropriate for sport or occupational assessments but are generally more difficult to standardise.
The client pushes the lateral aspect of the trunk directly into the Muscle Meter while resistance is provided manually or against a fixed support.
This protocol is simple and quick to perform but may be limited by the examiner's ability to resist stronger clients.
Explain the assessment.
"We're going to measure how much force you can produce when pushing your trunk sideways into the Muscle Meter. Build the pressure gradually, push as hard as you safely can and tell me immediately if you experience pain or unusual symptoms."
Record:
current symptoms
stiffness
fatigue
confidence
recent flare-ups
Maintain:
upright sitting
neutral pelvis
feet flat
hips and knees at approximately 90°
arms crossed
trunk neutral
Position the pusher cap against the lateral aspect of the upper trunk, immediately inferior to the axilla over the lateral rib cage.
Avoid direct pressure over painful ribs or bony prominences.
Record the exact contact point to improve repeatability.
Minimise:
pelvic movement
trunk rotation
shoulder elevation
leaning forwards or backwards
pushing through the feet
Use consistent cueing.
"Push your shoulder towards the Muscle Meter."
"Build the pressure gradually."
"Push as hard as you safely can."
"Hold."
"Keep breathing."
6. Record trials
Use:
1–2 familiarisation trials
2–3 maximal trials
3–5 second contractions
45–90 seconds rest
Record either:
highest force, or
average force
Maintain the same scoring method at reassessment.
Repeat the assessment if:
pelvis shifts
trunk rotates
feet lift
device slips
shoulder elevates excessively
pain unexpectedly limits effort
examiner cannot stabilise the device
The puller strap protocol measures lateral flexion force while the client pulls sideways against a fixed anchor with the Muscle Meter positioned in-line.
This setup is often preferable for stronger clients because it reduces examiner influence and improves repeatability.
The same client position, trial numbers and scoring system should be used as the pusher cap protocol.
Record:
strap position
anchor height
anchor distance
Muscle Meter orientation
client position
Do not directly compare pusher cap and puller strap results, as they represent different testing protocols.Understanding the Result
Higher force values generally indicate greater lateral trunk strength for that specific testing setup.
Lower values may reflect:
pain
fatigue
guarding
poor familiarisation
reduced confidence
inconsistent stabilisation
altered trunk positioning
The assessment is most valuable when compared with:
previous assessments
left versus right sides
trunk flexion and extension strength
rotational strength
symptoms
functional capacity
occupational demands
sporting requirements
A single result should never be interpreted in isolation.
Published Muscle Meter normative data for spinal lateral flexion are currently unavailable.
Similarly, published handheld dynamometry reference values for isolated trunk lateral flexion are limited because testing positions, stabilisation methods and equipment differ considerably between studies.
For this reason, the most meaningful comparisons are:
the client's own baseline
left versus right comparison
repeated measurements over time
associated symptoms
confidence during testing
functional performance
A side-to-side difference of approximately 10% or greater may warrant further investigation when accompanied by symptoms, reduced confidence or altered function.
Published normative data should be used only as general context and not as pass/fail criteria.
Interpret relative to growth, coordination and sporting participation.
Useful for baseline assessment, monitoring strength changes and exercise progression.
Interpret alongside balance, walking, transfers and activities of daily living.
Particularly useful for sports requiring trunk stability during sprinting, cutting, tackling, throwing, rowing and lifting.
Useful for manual handling, carrying, lifting and physically demanding occupations.
Interpret alongside pain, confidence, movement quality and functional tolerance rather than muscle strength alone.
Common errors include:
trunk rotation
pelvic movement
leaning forwards
leaning backwards
inconsistent device placement
inconsistent strap height
inconsistent verbal cueing
breath holding
Limitations include:
highly setup-dependent
examiner strength may influence handheld testing
pain may reduce maximal force
strength alone does not determine function
published Muscle Meter norms remain limited
This assessment may be useful for:
baseline trunk strength assessment
side-to-side comparison
monitoring progress over time
athlete performance profiling
occupational strength assessment
objective reporting using Measurz
client education
It measures maximal isometric trunk lateral flexion strength in a standardised testing position.
Peak Force is the primary outcome measure.
Yes. Bilateral assessment is recommended because side-to-side comparison is often more clinically meaningful than absolute force values.
No. It measures force production only and should always be interpreted alongside other assessment findings.
The pusher cap provides a simple, fast assessment. Puller straps may provide greater consistency when testing stronger clients.
Measures maximal isometric spinal lateral flexion strength.
Can be performed using either the Muscle Meter pusher cap or puller straps.
Peak Force is the primary routine outcome measure.
Compare left and right sides using the same protocol.
Standardise positioning, device placement and instructions to improve repeatability.
Measurz can calculate additional force-time metrics beyond peak force.
Compare results with the client's own baseline rather than relying on published norms.
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, 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
Stark, T., Walker, B., Phillips, J. K., Fejer, R., & Beck, R. (2011). Hand-held dynamometry correlation with the gold standard isokinetic dynamometry: A systematic review. PM&R, 3(5), 472–479.
This follows the improved evidence-first structure from your spinal flexion article while adapting it specifically for spinal lateral flexion. It also maintains the same writing style and level of detail so the two articles are consistent within the Measurz knowledge base.
