The Ankle Inversion Strength Test measures the maximum isometric force produced when the client pushes the inside of the foot against the Anker. It provides an objective measure of ankle invertor strength and is commonly used for baseline testing, side-to-side comparison and monitoring changes over time.
The assessment primarily evaluates the tibialis posterior and tibialis anterior, with contributions from the flexor hallucis longus and flexor digitorum longus depending on foot position. These muscles play an important role in foot stability, medial arch support, walking, running and change-of-direction activities.
When used with Measurz, the Anker records peak force and can also calculate additional metrics including force relative to body weight, impulse, torque (when the lever arm is entered), rate of force development, time to peak and fatigue index.
The assessment measures strength only and should always be interpreted alongside symptoms, movement assessment and functional performance.
The Ankle Inversion Strength Test is an isometric assessment where the client pushes the inside of the foot against the Anker without producing visible ankle movement.
Using the Anker's four independent load cells allows the assessment to be performed in a fixed, repeatable position, reducing variability between testing sessions when the same setup is maintained.
Explain that the assessment measures how strongly they can push the inside of their foot against the Anker.
Record any:
ankle pain
swelling
stiffness
recent injury
previous surgery
neurological symptoms
fatigue
Complete one or two submaximal practice contractions before maximal testing.
Seat the client with:
hips flexed approximately 90°
knees flexed approximately 90°
pelvis against the backrest
trunk upright
feet facing forwards
Use the same seated position during every reassessment.
Position the testing foot so that:
the heel is centred on the footplate
the second metatarsal aligns with the centre of the platform
the ankle begins in a neutral position
the tibia remains vertical
Position the medial load cell against the medial border of the first metatarsal head. Avoid contact with the medial malleolus or the toes.
Record the contact point so it can be reproduced during future testing.
Prevent movement of the pelvis, trunk, hip and knee throughout the assessment.
Only the ankle should generate force into the load cell.
Use consistent verbal instructions.
"Push the inside of your foot into the pad."
"Build the pressure smoothly."
"Push as hard as you can."
"Hold."
"Keep breathing."
Repeat the same cueing during every reassessment.
Use:
1–2 practice trials
2–3 maximal trials
3–5 second contractions
30–60 seconds rest between trials
Record either:
the highest trial, or
the average of the recorded trials
Use the same scoring method for future testing.
the heel lifts
the foot rotates
the knee moves
the pelvis shifts
the trunk leans
the load cell loses contact
pain limits maximal effort
the client starts before instructed
The assessment may be useful for:
baseline ankle strength assessment
left versus right comparison
monitoring changes following reduced loading
lower-limb strength profiling
athlete performance assessment
objective progress tracking
monitoring response to exercise
client education
The assessment should support clinical reasoning and should not be used as a stand-alone diagnostic or clearance assessment.
The primary outcome is peak isometric ankle inversion force.
When analysed in Measurz, additional metrics may include:
Peak force
Force relative to body weight
Impulse
Torque
Rate of force development
Time to peak
Fatigue index
The assessment does not directly measure:
ankle joint mobility
ligament integrity
tendon pathology
balance
gait quality
readiness for sport or work
Higher force values generally indicate greater ankle inversion strength in the tested position.
Lower values may be influenced by:
pain
fatigue
apprehension
reduced effort
previous injury
poor familiarisation
inconsistent positioning
When interpreting results:
Compare with the client's previous assessment.
Compare left and right limbs.
Consider symptoms during testing.
Assess movement quality and compensations.
Relate the findings to the client's functional goals.
Published Anker-specific normative values are currently unavailable.
Research using handheld and fixed dynamometry has demonstrated that ankle inversion strength can be measured reliably when testing procedures are standardised. However, reported values differ between studies due to differences in positioning, stabilisation and equipment. For this reason, comparing results with the client's own baseline and the opposite limb is generally more meaningful than comparing absolute force values with published studies.
Healthy individuals commonly demonstrate less than a 10% side-to-side difference in ankle strength. Larger asymmetries should be interpreted alongside symptoms, previous injury and functional performance rather than used as an isolated finding.
Youth
Use additional familiarisation trials and interpret results relative to age, growth and activity level.
Adults
Useful for baseline strength assessment and monitoring progress over time.
Older adults
Interpret alongside walking ability, balance and daily function.
Athletes
Useful as part of a comprehensive lower-limb strength profile for running, jumping, cutting and landing activities.
Clients with persistent symptoms
Interpret results alongside pain, confidence, movement quality and functional performance.
Common errors include:
inconsistent foot placement
heel lifting
excessive toe gripping
trunk movement
pelvis shifting
incorrect load cell placement
inconsistent verbal instructions
allowing ankle plantarflexion during the contraction
Limitations include:
results are specific to the testing setup
pain may reduce force production
muscle strength alone does not determine functional performance
published Anker-specific normative values are currently limited
The assessment may be useful for:
establishing a baseline
monitoring strength changes over time
comparing left and right limbs
athlete profiling
lower-limb performance assessment
objective reporting using Measurz
educating clients about measurable progress
It measures maximal isometric ankle inversion strength.
Peak force is the primary outcome measure for routine testing.
No. It measures force production only and should be interpreted alongside other assessment findings.
Yes. Bilateral testing allows meaningful side-to-side comparison.
Small changes in foot position, ankle angle or load cell contact can significantly influence force measurements, making consistent positioning essential for accurate retesting.
Measures maximal isometric ankle inversion strength.
Primarily assesses the tibialis posterior and tibialis anterior.
Peak force is the primary outcome measure.
Measurz can provide additional force-time metrics.
Consistent positioning improves repeatability.
Compare results with previous assessments and the opposite limb rather than relying solely on published reference values.
Alfuth, M., & Hahm, M. M. (2016). Reliability, comparability, and validity of foot inversion and eversion strength measurements using a hand-held dynamometer. International Journal of Sports Physical Therapy, 11(1), 72–84.
Mentiplay, B. F., Perraton, L. G., Bower, K. J., Adair, B., Pua, Y. H., Williams, G. P., McGaw, R., & Clark, R. A. (2015). Assessment of lower limb muscle strength and power using hand-held and fixed dynamometry: A reliability and validity study. PLOS ONE, 10(10), e0140822.
Martins, J., da Silva, J. R., da Silva, M. R. B., & Bevilaqua-Grossi, D. (2017). Validation of ankle strength measurements by means of a hand-held dynamometer in adult healthy subjects. Rehabilitation Research and Practice, 2017, 5426031.
