The Ankle Inversion Strength Test measures how much force a client can produce when turning the sole of the foot inward against resistance. It is commonly used to assess inversion force output from muscles such as tibialis posterior, tibialis anterior and related medial ankle contributors in a controlled isometric setup.

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 and fatigue index.

For routine ankle inversion testing, peak force is usually the main metric. Force as a percentage of body weight may be useful if it is directly calculated from the test force and the client’s body weight. Rate of force development and time to peak may be useful when rapid ankle control is relevant, such as cutting, landing, change-of-direction or reactive balance tasks. Impulse may be useful if sustained force over a defined time window is intentionally tested. Fatigue index is only relevant if repeated or sustained inversion efforts are part of the protocol.

The result can support baseline assessment, side-to-side comparison and progress tracking, but it does not diagnose ankle pathology, tendon dysfunction, instability, injury status or readiness for sport or work on its own.

What Is the Ankle Inversion Strength Test?

The Ankle Inversion Strength Test is an isometric force assessment where the client attempts to turn the foot inward into the Muscle Meter without visible ankle movement. The device is usually placed on the medial side of the foot, commonly around the medial forefoot or first metatarsal region.

The movement direction is ankle inversion. The purpose of the test is to measure force output in an inward-turning direction at the ankle and foot.

Consistent setup matters because ankle angle, foot position, contact point, lower-leg stabilisation, strap angle and compensation can all change the result. This test does not fully measure dynamic ankle control, balance, walking, running, cutting, landing or sport performance on its own.

Step-by-Step Protocol / Practice

1. Prepare the client

Explain that the test measures how strongly they can turn the foot inward against the Muscle Meter. Record baseline symptoms, medial ankle discomfort, arch discomfort, tendon-region symptoms, recent activity, fatigue and confidence with maximal effort.

Use at least one submaximal practice trial so the client understands the direction of force.

2. Set the client position

A common setup is seated with the hip and knee flexed and the ankle near neutral. Supine or long-sitting setups can also be used, but the same position should be repeated at retest.

Record:

• Seated, supine or long-sitting position
• Knee angle
• Ankle start position
• Foot position
• Whether footwear was removed
• Whether the lower leg was stabilised

3. Set up the device or straps

For a handheld setup, the professional resists the inversion force with the Muscle Meter. For stronger clients or improved repeatability, a strap-stabilised or fixed setup may be used.

If using a strap, record the anchor point, strap angle, strap length, foot position and whether the anchor stayed stable.

4. Place the device, strap or handle

Place the Muscle Meter against the medial side of the forefoot, commonly near the first metatarsal region. Avoid pressure over sensitive bony areas or painful tendon regions.

The force direction should oppose inversion. The client attempts to turn the sole inward into the device without lifting or twisting the entire leg.

5. Stabilise the position

Stabilise the lower leg so the client does not compensate with hip rotation, knee movement, toe curling, ankle plantarflexion, dorsiflexion or whole-leg movement. The aim is controlled ankle inversion force.

6. Give clear instructions

Use consistent instructions such as:

“Turn your foot inward into the device as hard as you can and hold.”
“Build up smoothly, then push hard.”
“Keep the knee and leg still.”
“Try not to curl your toes or twist the whole leg.”
“Tell me if you feel pain, cramping, tingling or anything unusual.”

7. Record trials

Use 1–2 practice trials, then record 2–3 maximal trials. A common contraction duration is 3–5 seconds. Rest for 30–60 seconds between trials, or longer if symptoms, fatigue or cramping occur.

Record whether the final score is the best trial or the average of recorded trials. Use the same method at retest.

8. Identify invalid trials

Repeat or mark a trial as invalid if:

• The hip rotates
• The knee moves
• The lower leg lifts or twists
• The device slips
• The strap or anchor moves
• The client plantarflexes or dorsiflexes instead of inverting
• Toe gripping dominates the effort
• Pain limits the contraction
• The professional cannot hold the device steady

9. Record symptoms

Record medial ankle pain, arch discomfort, tendon-region symptoms, cramping, paraesthesia, confidence, apprehension and symptom response after testing. Do not repeatedly test through high pain or worsening symptoms.

For retesting, match the same position, device placement, instructions, contraction duration, rest period, scoring method and symptom recording.

Why It Is Used

The Ankle Inversion Strength Test is used to quantify inversion force output in a repeatable setup. It may be useful for:

• Baseline ankle strength assessment
• Side-to-side comparison
• Monitoring change over time
• Strength profiling for running and change-of-direction sports
• Assessing medial ankle force capacity
• Comparing inversion with eversion strength
• Supporting balance and lower-limb control reasoning
• Workplace context where walking, uneven surfaces or ladder use are relevant
• Fitness and performance progress tracking
• Client education

What It Measures

The test primarily measures isometric ankle inversion force output in the chosen setup. It reflects the client’s ability to produce force in an inward-turning direction at the ankle and foot.

It does not diagnose tendon pathology, ankle instability, nerve involvement, balance capacity, foot posture or readiness for sport or work. It also does not fully measure dynamic control during cutting, landing, running or uneven-ground walking.

Understanding the Result, Reference Values and What to Look For

What a higher or lower result may suggest

A higher score may suggest greater inversion force output in that specific test setup. A lower score may suggest reduced inversion force output, but the reason should be interpreted carefully.

Lower force may reflect pain, apprehension, poor familiarisation, fatigue, guarding, inconsistent device placement, poor stabilisation, medial ankle sensitivity, reduced confidence or compensation.

One result should not be interpreted in isolation. Interpretation is strongest when the same setup is repeated over time and reviewed alongside symptoms, confidence, movement quality, eversion strength, dorsiflexion strength, calf capacity, ankle ROM, balance, hopping, cutting or work-specific tasks.

What can influence the result

Important influences include:

• Pain
• Apprehension
• Poor familiarisation
• Fatigue
• Guarding
• Poor stabilisation
• Hip rotation compensation
• Toe gripping
• Different device placement
• Different strap angle
• Different knee or ankle position
• Foot posture
• Breath holding
• Client confidence
• Professional strength if using handheld resistance

Normative, reference and comparative values

Published Muscle Meter-specific ankle inversion norms are limited. Because of this, reference values should be used as context only and not as direct targets unless the protocol is closely matched.

More user-friendly comparison data include:

• In people with chronic ankle instability, published handheld dynamometry inversion values have been reported around 157.2–187.5 N. In practical terms, this is roughly similar to about 16–19 kg of force.
• In healthy participants, other handheld dynamometry inversion values have been reported around 19.5–22.0 kg, which is approximately 191–216 N.
• One healthy-control comparison value for inversion was reported around 127.5 N, or roughly 13 kg of force.
• These values vary because the studies used different positions, devices and stabilisation methods. A seated Muscle Meter result should not be directly compared with a side-lying, supine or belt-stabilised HHD result as if they are the same test.
• For side-to-side comparison, a difference of around 10% or more is often worth reviewing more closely in strength testing, especially if it matches symptoms, previous injury, poor confidence or a functional difference. This is not a strict pass/fail cut-off.
• Comparing inversion with eversion can also be useful. Large differences between directions may provide context, especially when paired with balance, hopping, change-of-direction or sport/work tasks.

If you calculate force as a percentage of body weight in Measurz, use it mainly for the client’s own baseline, side-to-side comparison and retesting. Published bodyweight-percentage norms for this exact Muscle Meter inversion setup are not currently strong enough to use as universal targets.

These values are best used as comparison data. They can help provide context, but they should not be used as diagnostic, clearance or pass/fail cut-offs.

Practical interpretation priorities

Use this order:

1. Compare with the client’s own baseline.
2. Compare right and left sides when relevant.
3. Compare inversion and eversion where relevant.
4. Consider symptoms during and after testing.
5. Consider confidence and effort quality.
6. Review whether compensations were present.
7. Compare with related strength, mobility or performance tests.
8. Relate the result to the client’s sport, work, exercise or daily-life demands.
9. Retest under the same conditions to monitor change.
10. Do not use reference values as pass/fail criteria.

What to look at for each relevant Muscle Meter metric

Peak force
Use for maximum inversion force output, baseline strength, side-to-side comparison, inversion-to-eversion comparison, progress tracking and comparing force across retests. Look for best score or average score, consistent setup, side-to-side difference, change from baseline, pain response and compensation during maximal effort.

Force as percentage of body weight
Use only when calculated directly from test force and body weight. Look for changes over time and differences between sides, but do not treat it as a universal target unless the comparison data use the same method.

Rate of force development
Use when rapid ankle control is relevant, such as cutting, landing, agility, change-of-direction or reactive balance tasks. Look for early force production and whether RFD changes while peak force stays similar.

Time to peak
Use to understand whether force is produced quickly or gradually. Look for delayed peak force, faster time to peak across retests, and whether a slower time reflects caution, pain, poor cueing or an actual performance difference.

Impulse
Use only if a defined sustained force window is intentionally tested. Look for whether the client can sustain force briefly and whether impulse improves while peak force stays similar.

Fatigue index
Use only if repeated or sustained inversion efforts are part of the protocol. Look for drop-off across repeated trials, symptom-related fatigue and whether fatigue improves across a training block.

Assessing and Providing Context for Different Client Populations

Youth clients
Consider growth, maturation, coordination, training age, attention and familiarisation. Clear instructions and practice trials are important.

Adults and general fitness clients
Use the test for baseline strength, side-to-side comparison and progress tracking. Compare results with balance, calf strength, ankle mobility and general exercise goals.

Older adults
Consider balance, transfers, daily tasks, walking confidence, uneven surfaces, fatigue, rest periods and function. Lower force may provide useful context but should not be interpreted without function.

Athletes and sport clients
Consider cutting, pivoting, landing, sprinting, jumping and change-of-direction demands. Peak force alone does not equal sport performance.

Workplace and manual task clients
Consider uneven ground, ladders, carrying, prolonged standing, stairs, bracing and footwear demands. Do not use one score to clear work duties.

Clients returning after injury
Use the test to monitor force output, confidence and symptom response. Strength alone should not confirm readiness.

Clients with pain or persistent symptoms
Pain, fear, guarding, fatigue, apprehension and confidence may reduce force. Record symptom response carefully and compare with related tests.

Higher body mass clients
Absolute force and force relative to body mass may both be useful. Interpret results in relation to goals, symptoms and functional demands.

Reliability, Validity and Measurement Considerations

Repeatability improves when the same setup is used each time. Record and standardise:

• Same test position
• Same device attachment
• Same device placement
• Same strap setup, if used
• Same anchor height and distance, if straps are used
• Same strap angle, if straps are used
• Same knee and ankle position
• Same stabilisation
• Same instructions
• Same contraction duration
• Same rest period
• Same scoring method
• Same symptom and compensation recording

Belt-stabilised handheld dynamometry for ankle inversion and eversion has shown reliable results in healthy adults, but values can differ depending on position. Handheld dynamometry values can also vary depending on whether the device is held manually or stabilised with a belt. This means internal consistency is more useful than comparing results from different protocols.

Common Errors and Limitations

Common errors include:

• Device placement changing between trials
• Foot twisting instead of controlled inversion
• Hip rotation compensation
• Knee movement
• Toe gripping
• Plantarflexion or dorsiflexion substitution
• Poor lower-leg stabilisation
• Strap or anchor movement
• Breath holding
• Testing through high pain
• Comparing sitting, supine and side-lying results as if identical
• Treating the score as a diagnosis

Limitations include:

• Testing is setup-dependent
• Manual resistance may be limited by professional strength
• Strap setup requires careful anchor control
• Muscle Meter-specific universal norms may be limited
• Published inversion norms are less complete than dorsiflexion and plantarflexion norms
• Pain, fear or guarding can reduce force output
• Peak force does not measure endurance or movement quality
• Strong symmetry does not automatically indicate readiness for sport or work

Practical Applications

The Ankle Inversion Strength Test may be useful for:

• Baseline assessment
• Side-to-side comparison
• Inversion-to-eversion comparison
• Strength profiling
• Monitoring response to exercise or intervention
• Reviewing medial ankle force capacity
• Supporting balance and agility assessment reasoning
• Client education
• Comparing with related ankle, calf and foot tests

Ideas to Make the Result Better

If force is low on both sides, consider assessing ankle ROM, foot strength, calf capacity, balance, gait, confidence and general lower-limb strength.

If one side or direction is much lower, compare with symptoms, injury history, eversion strength, ankle mobility, balance, hopping and change-of-direction tasks.

If pain limits the result, record symptom location and review whether device placement, ankle position or effort level needs modification.

If force is good but function is limited, compare with dynamic tasks such as single-leg balance, hopping, cutting, step-downs, walking tolerance or sport-specific demands.

If the client is improving, keep the same test setup and monitor whether force, symptoms, confidence and function improve together.

Recommended Standard Protocol Summary

Position: Seated, hip and knee flexed, ankle near neutral
Start position: Foot relaxed, ankle close to neutral
Joint or trunk angle: Record knee and ankle position
Trials: 1–2 practice trials, then 2–3 recorded trials
Contraction duration: 3–5 seconds
Rest: 30–60 seconds between efforts
Metric: Peak force, plus percentage of body weight only if directly calculated
Attachment or device setup: Muscle Meter against medial forefoot near first metatarsal region, or strap-stabilised if used
Final score: Best trial or average of trials
Key retesting requirement: Same position, device placement, instructions, contraction duration, rest and scoring method

FAQs

What does the Ankle Inversion Strength Test measure?

It measures isometric ankle inversion force output in a specific test setup.

Should the result be recorded as percentage of body weight?

It can be if you calculate it directly from test force and body weight. Use it for internal comparison rather than as a universal target.

Are there universal inversion norms for the Muscle Meter?

Published universal Muscle Meter norms for this exact protocol appear limited. Baseline, side-to-side comparison, inversion-to-eversion comparison and repeated testing are usually more useful.

What numerical values are available for comparison?

Published comparison values include inversion forces around 157.2–187.5 N, 191–216 N, and 127.5 N from different handheld dynamometry examples. These are not direct Muscle Meter targets unless the protocol is closely matched.

Can this test diagnose ankle instability or tendon pathology?

No. It can measure force output, but it does not diagnose a condition or explain symptoms on its own.

Should inversion be compared with eversion?

Yes, inversion-to-eversion comparison can be useful, but interpretation should include symptoms, history, setup quality and functional findings.

What can make the result unreliable?

Different device placement, ankle angle, hip rotation, toe gripping, poor stabilisation, pain and inconsistent instructions can affect results.

What should be recorded in Measurz?

Record side, position, device placement, peak force, percentage of body weight if directly calculated, symptoms, compensations, confidence, scoring method and related findings.

Key Takeaways

• The Ankle Inversion Strength Test measures isometric inversion force output.
• Peak force is usually the main routine Muscle Meter metric.
• Published examples include approximately 157.2–187.5 N, 191–216 N, and 127.5 N, but protocols vary.
• Percentage of body weight should only be used when calculated directly from force and body weight.
• Baseline comparison, side-to-side comparison and inversion-to-eversion comparison are usually more useful than broad norms.
• Reference values provide context, not diagnostic or clearance cut-offs.
• Measurz should capture setup, symptoms, bodyweight-normalised values where directly calculated, compensations and retesting conditions.

References

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. https://doi.org/10.1371/journal.pone.0140822

Spink, M. J., Fotoohabadi, M. R., Menz, H. B., & Lord, S. R. (2010). Foot and ankle strength assessment using hand-held dynamometry: Reliability and age-related differences. Gerontology, 56(6), 525–532. https://doi.org/10.1159/000264655