Range of Motion: Knee Prone heel to butt

The Knee Prone Heel-to-Butt Test assesses how close the heel can move toward the buttock in prone. It provides useful information about knee flexion range, anterior thigh mobility, symptom response and side-to-side differences.

Introduction

The prone heel-to-butt position is a practical way to assess knee flexion in a prone position and observe anterior thigh mobility. It is often related to the Ely or prone knee flexion test, but for Measurz tracking it should be treated as a ROM and movement comparison test unless a specific orthopaedic protocol is being used.

This test can be recorded as a distance measure, angle measure or qualitative observation. For best tracking, record the method consistently.

Quick Summary

• Assesses prone knee flexion and anterior thigh mobility.
• Can be measured in degrees or heel-to-butt distance.
• Useful for side-to-side comparison.
• Pelvic control is essential.
• Does not explain the cause of restriction on its own.

What Is the Knee Prone Heel-to-Butt Test?

The test is performed with the client lying prone while the knee is flexed toward the buttock. It can be performed actively or passively.

It may be used to observe:

• knee flexion ROM
• anterior thigh stretch response
• pelvic movement
• hip flexion compensation
• symptom response
• side-to-side differences

Why It Is Used

It is used to:

• monitor prone knee flexion mobility
• assess anterior thigh length context
• compare left and right sides
• track progress across sessions
• support exercise range decisions
• add context to squat, lunge, running and kicking tasks

What It Measures

This test measures prone knee flexion range and the client’s response to anterior thigh lengthening. Depending on the method, the score may be:

• knee flexion angle in degrees
• heel-to-butt distance in centimetres
• qualitative result such as “heel contacts buttock” or “pelvis lifts before end range”

Who It Is Useful For

Useful for:

• field and court athletes
• runners and kickers
• clients returning to kneeling, lunging or sprinting
• general fitness clients with anterior thigh mobility goals
• professionals tracking ROM alongside strength and function

Equipment Required

• Firm plinth or mat
• Inclinometer, goniometer or tape measure
• Optional pelvic stabilisation strap
• Pain scale
• Measurz recording profile

Step-by-Step Protocol / Practice

1. Client position. Lie prone with hips neutral and legs relaxed.
2. Pelvic setup. Keep the pelvis level. Consider a strap or firm manual stabilisation if consistency is important.
3. Active test. Ask the client to bend the knee and bring the heel toward the buttock as far as comfortable.
4. Passive test. If appropriate, gently flex the knee until the first firm resistance, symptom limit or pelvic compensation.
5. Measure. Record knee flexion angle or heel-to-butt distance. Do not mix methods without noting it.
6. Observe compensation. Watch for hip flexion, anterior pelvic tilt, lumbar extension or the hip lifting from the table.
7. Ask about symptoms. Record anterior thigh stretch, knee pressure, pain score and location.
8. Repeat. Use consistent trials and side order.
9. Stop if needed. Stop if symptoms increase sharply, the client guards strongly or the test is not appropriate.

Scoring and Interpretation

Possible scoring options:

• knee flexion angle in degrees
• heel-to-butt distance in centimetres
• whether heel contact is achieved
• symptom response and compensation timing

A smaller heel-to-butt distance or larger knee flexion angle generally reflects more available range in prone. However, interpretation depends on pelvis control and whether the movement was active or passive.

If the pelvis lifts early, the score may reflect compensation rather than true knee flexion or anterior thigh mobility.

Normative Data, Benchmarks or Reference Values

Evidence level: Level 3 — limited exact norms; use practical comparison guidance.

Published normative values for this exact heel-to-butt protocol, device, distance method and population appear limited. Related knee flexion reference values can provide broad context, but prone heel-to-butt testing is position-specific and should not be treated as identical to supine knee flexion.

Use:

• baseline score
• left/right comparison
• active versus passive difference
• heel-to-butt distance or degrees
• pain score
• pelvic compensation timing
• sport or task goal
• repeated testing under the same setup

Reliability and Validity

A related 2020 study on the Ely and Active Knee Extension tests reported reliability and MDC values for prone knee flexion and AKE testing in asymptomatic adults, supporting the importance of pelvic control and repeatable technique.  

The same study is useful context but should not be over-applied to every heel-to-butt protocol because scoring method, population and stabilisation may differ. If using heel-to-butt distance rather than angle, measurement error may be different.

Sensitivity and Specificity

For this ROM-style heel-to-butt assessment, sensitivity and specificity are not usually applicable because the test is being used to measure range, symptoms and movement behaviour rather than identify a condition.

Common Errors and Limitations

• allowing the pelvis to lift
• forcing the heel toward the buttock
• failing to record active versus passive
• mixing distance and angle scores
• ignoring symptom location
• comparing different test positions
• assuming a positive Ely-style response explains the cause
• not recording whether the heel contacted the buttock

Practical Applications

This test can help with:

• monitoring anterior thigh mobility
• comparing sides after training or irritation
• tracking tolerance to kneeling or sprinting preparation
• guiding quad mobility and knee flexion exposure
• informing programming alongside strength and functional testing

How to Record This in Measurz

Record:

• test name: Knee Prone Heel-to-Butt
• side
• active or passive
• score in degrees or centimetres
• whether heel contacted buttock
• pain score
• symptom location
• pelvic compensation
• device or tape measure used
• baseline
• comparison side
• retest date
• related knee flexion, hip extension or strength findings

Example: “Right prone heel-to-butt: 7 cm gap, passive, pain 1/10 anterior thigh stretch, mild pelvic lift at end range. Left: 2 cm.”

Related Tests / Internal Links

• Knee Flexion Test
• Knee Extension Test
• Hip Extension Test
• Hip Modified Thomas Test
• 90/90 Active Knee Extension Test

FAQs

What does the prone heel-to-butt test measure?
It measures prone knee flexion range and anterior thigh mobility context.

Should I record distance or degrees?
Either can be used, but degrees are often better for ROM tracking. Use the same method each time.

What if the pelvis lifts during the test?
Record it as a compensation because it may change the meaning of the result.

Does this test identify why the knee cannot bend fully?
No. It provides movement information and should be interpreted with other findings.

Key Takeaways

• Pelvic control is essential.
• Record method, side, symptoms and compensation.
• Use baseline and side-to-side comparison.
• Do not treat heel-to-butt distance as a universal pass/fail measure.

References

Olivencia, O., Godinez, G. M., Dages, J., Duda, C., Kaplan, K., Kolber, M. J., Kaplan, P. T., & Kolber, M. J. (2020). The reliability and minimal detectable change of the Ely and Active Knee Extension tests. International Journal of Sports Physical Therapy, 15(5), 776–782. https://doi.org/10.26603/ijspt20200776

Santos, H. H., et al. (2025). Reliability of range of motion measurements obtained by goniometry, photogrammetry and smartphone applications in the lower limbs: A systematic review. Journal of Bodywork and Movement Therapies.