The Knee Flexion Test measures how far the knee can bend. It is useful for tracking knee mobility, comparing sides and monitoring changes related to squatting, kneeling, cycling, running and lower-limb training.
A client may struggle to kneel, squat deeply, cycle comfortably, sit back on the heels or bend the knee after a period of pain or swelling. The Knee Flexion Test gives a repeatable way to measure knee bending range of motion and track change over time.
Knee flexion is important for many everyday and training tasks, but the score should not be interpreted on its own. Stronger interpretation comes from combining knee flexion ROM with pain, swelling, side-to-side comparison, knee extension ROM, strength, squat ability, kneeling tolerance and functional movement findings.
Test name: Knee Flexion Test
Purpose: Assess knee flexion range of motion
What it assesses: The ability to bend the knee
Equipment: Measurz inclinometer or equivalent inclinometer
Key finding: Knee flexion angle in degrees
Best used with: Knee extension, prone heel-to-butt, hip ROM, squat, sit-to-stand and lower-limb strength testing
Key limitation: Knee flexion ROM does not explain the cause of restriction on its own.
The Knee Flexion Test measures how far the knee bends. In this protocol, the client lies prone while the knee flexes, and an inclinometer is placed on the tibia to record the knee flexion angle in degrees.
The test can be performed actively or passively. Active testing records how far the client can bend the knee using their own effort. Passive testing records how far the knee can bend when the professional assists the movement.
The Knee Flexion Test is used to:
Establish baseline knee ROM.
Compare left and right sides.
Track progress across sessions.
Add context to squatting, kneeling, cycling and stairs.
Monitor changes after pain, swelling or reduced loading.
Support lower-limb programming decisions.
Identify whether related strength or functional testing may be useful.
The test measures knee flexion ROM in degrees.
It does not directly measure:
Quadriceps flexibility alone.
Knee strength.
Swelling.
Pain source.
Squat depth capacity.
Kneeling tolerance.
Running readiness.
Overall lower-limb function.
A lower knee flexion result may indicate reduced bending range under the tested method, but it does not explain the cause by itself.
Active knee flexion means the client bends the knee using their own effort.
Passive knee flexion means the professional assists the knee into flexion while the client remains relaxed.
Both methods can be useful, but they should be labelled separately. Active ROM may be influenced by strength, control, pain, swelling or apprehension. Passive ROM may provide more information about available assisted range. When retesting, repeat the same method.
This test may be useful for:
Athletes.
Gym clients.
Runners.
Cyclists.
Older adults.
Lower-limb progress tracking.
Clients returning to squatting, kneeling, stairs or sport tasks.
Clients monitoring knee mobility across a training or rehabilitation block.
Use caution when the client has acute knee pain, recent injury, high irritability, swelling, recent surgery, neurological symptoms or pain that meaningfully changes movement quality.
Measurz inclinometer or equivalent inclinometer.
Table or mat.
Measurz app.
Notes for side, active/passive method, pelvic movement, pain and symptoms.
Ask the client to lie prone on a table or mat. Start with the knee extended and the leg relaxed.
Ensure the pelvis stays level and the hip does not rotate. The test should measure knee flexion rather than pelvic lift or hip movement.
Open the Measurz inclinometer or equivalent device. Place the inclinometer on the tibia according to the chosen protocol.
Ask the client to bend the knee and bring the heel toward the glute as far as comfortable.
Use consistent wording, such as:
“Bend your knee and bring your heel toward your glute as far as you comfortably can, without lifting the pelvis.”
Watch for pelvic lift, hip rotation, trunk movement, pain or altered effort.
At the end of the movement, pause and save the knee flexion angle in degrees.
If testing passively, assist the knee into flexion and clearly record that passive testing was used.
Repeat the same method on the other side when side comparison is useful.
Stop if pain meaningfully changes the movement, the pelvis lifts, the hip rotates, symptoms increase or the client cannot maintain the test position.
Record knee flexion in degrees.
Compare:
Left versus right side.
Active versus passive ROM, if both are tested.
Baseline versus retest.
Knee flexion with knee extension ROM.
ROM with pain, swelling or stiffness.
ROM with squat, kneeling, stairs, cycling or sit-to-stand findings.
A lower score may provide useful movement information, but interpretation should include pain, symptoms, pelvic compensation, side comparison, knee extension ROM and functional findings.
Evidence level: Level 1–2 — published reference values and functional benchmarks are available.
A large CDC joint range of motion study measured more than 600 people without known joint mobility conditions and reported age- and sex-specific knee flexion reference values. Relevant values include:
Age 9–19: females 142.3°, males 142.2°
Age 20–44: females 141.9°, males 137.7°
Age 45–69: females 137.8°, males 132.9°
These values show that knee flexion varies by age and sex, so a single universal target is too simplistic.
For practical Measurz interpretation, approximately 130–140° is a useful general reference range for many adults, but it should not be treated as a strict pass/fail rule. Some clients may need more range for deep squatting, kneeling or sitting back on the heels, while others may function well with less depending on their goals and tasks.
Functional knee flexion demands also vary by activity. Rowe and colleagues reported that gait and slopes required less than 90°, stairs and chairs required approximately 90–120°, and getting in and out of a bath required approximately 135° of knee flexion in an older adult sample. They suggested 110° may be a suitable functional rehabilitation goal for many daily tasks, while recognising that higher-flexion activities require more range.
Use reference values with:
Side-to-side comparison.
Baseline change.
Active/passive method.
Symptoms and swelling.
Pelvic compensation.
Activity demands.
Related strength and functional test findings.
Recent lower-limb ROM evidence shows that ROM reliability can vary substantially by tool, joint, assessor and protocol. A 2025 systematic review reported broad reliability ranges across goniometry, photogrammetry and smartphone methods. This supports the need for consistent testing setup when monitoring knee flexion ROM.
Fraeulin et al. found that digital inclinometer and related ROM measurement methods can be reliable when performed with standardised procedures. Kiatkulanusorn et al. also reported that clinical goniometric devices can vary in concurrent validity and reliability, reinforcing that device placement, tester consistency and protocol control matter.
For knee flexion, repeatability depends heavily on:
Consistent prone position.
Consistent tibial landmarking.
Clear active versus passive method.
Monitoring pelvic lift.
Consistent instructions.
Same device or measurement method.
Recording symptoms and compensation.
No universal SEM, MDC or MCID should be assumed for this exact Measurz knee flexion protocol unless the same method, device and population are used.
Common errors include:
Allowing the pelvis to lift.
Allowing hip rotation.
Changing between active and passive testing without recording it.
Placing the inclinometer inconsistently.
Forcing movement into symptoms.
Failing to record pain or swelling.
Comparing different positions directly.
Assuming knee flexion ROM explains squat or kneeling ability on its own.
Limitations include:
ROM does not identify the cause of restriction.
Active and passive ROM may differ.
Pain or swelling may reduce active range.
Pelvic compensation can inflate the score.
Non-weight-bearing ROM may not match functional movement.
Device placement can affect results.
Use the Knee Flexion Test for:
Baseline knee ROM.
Side-to-side comparison.
Progress tracking.
Programming context.
Monitoring changes across lower-limb training or mobility work.
Adding context to squats, kneeling, stairs, cycling and sit-to-stand tasks.
Deciding whether strength or functional testing would add useful information.
For example, a client with 118° knee flexion, swelling and difficulty descending stairs needs different interpretation from a client with 118° knee flexion, no symptoms and no limitation in their required activities.
Record:
Test name: Knee Flexion Test.
Side tested: left or right.
Score: knee flexion ROM in degrees.
Method: active or passive.
Position: prone.
Device: Measurz inclinometer or equivalent inclinometer.
Device placement: tibia or the chosen landmark.
Pain score: 0–10.
Symptom location: anterior knee, posterior knee, patellar region, quadriceps, hamstring, calf or other.
Symptom quality: stretch, stiffness, block, pinch, pain or pressure.
Pelvic compensation: pelvic lift, hip rotation or trunk movement.
Comparison side: opposite knee.
Related findings: knee extension ROM, prone heel-to-butt, hip ROM, squat, sit-to-stand, strength or functional tests.
Progress comments: whether ROM improved, symptoms changed or compensation reduced.
Retest date: for monitoring change.
This improves repeatability, client education and progress tracking.
Knee Extension Test
Knee Prone Heel-to-Butt Test
90/90 Active Knee Extension Test
Squat Assessment
5-Time Sit-to-Stand
Single-Leg Sit-to-Stand
Knee Strength Testing
Hip Range of Motion
Published reference values vary by age and sex. In a large CDC ROM study, adults aged 20–44 averaged about 141.9° for females and 137.7° for males, while adults aged 45–69 averaged about 137.8° for females and 132.9° for males.
Yes, 130–140° is a useful general reference range for many adults, but it is not a universal rule. The client’s age, symptoms, side-to-side comparison and activity demands matter.
Position the client prone, ask them to bend the knee, monitor pelvic movement and record the angle with an inclinometer.
Both can be useful. Active testing records the range the client can achieve themselves. Passive testing records the available assisted range. Record the method and repeat it consistently.
Functional demands vary. One study reported gait and slopes required less than 90°, stairs and chairs required about 90–120°, and bath transfers required about 135°.
It provides movement information and should be interpreted with pain, swelling, symptoms, strength, side comparison and functional tests.
The Knee Flexion Test measures knee bending ROM.
Pelvic control is important.
Record active or passive ROM.
Published adult reference values commonly sit around 133–142°, depending on age and sex.
130–140° is a useful practical reference, not a strict pass/fail rule.
Functional task demands vary from less than 90° to around 135° depending on the activity.
Track pain, side comparison and progress in Measurz.
Canever, J. B., Nonnenmacher, C. H., & Lima, K. M. M. (2025). Reliability of range of motion measurements obtained by goniometry, photogrammetry and smartphone applications in lower limb: A systematic review. Journal of Bodywork and Movement Therapies. DOI: 10.1016/j.jbmt.2025.01.009
Fraeulin, L., Holzgreve, F., Brinkbäumer, M., Dziuba, A., Friebe, D., Klemz, S., et al. (2020). Intra- and inter-rater reliability of joint range of motion tests using tape measure, digital inclinometer and inertial motion capturing. PLOS ONE, 15(12), e0243646. DOI: 10.1371/journal.pone.0243646
Kiatkulanusorn, S., Luangpon, N., Srijunto, W., Watechagit, S., Pitchayadejanant, K., Kuharat, S., Anwar Bég, O., & Paepetch Suato, B. (2023). Analysis of the concurrent validity and reliability of five common clinical goniometric devices. Scientific Reports, 13, 20915. DOI: 10.1038/s41598-023-48344-6
Rowe, P. J., Myles, C. M., Walker, C., & Nutton, R. (2000). Knee joint kinematics in gait and other functional activities measured using flexible electrogoniometry: How much knee motion is sufficient for normal daily life? Gait & Posture, 12(2), 143–155. DOI: 10.1016/S0966-6362(00)00060-6
Soucie, J. M., Wang, C., Forsyth, A., Funk, S., Denney, M., Roach, K. E., Boone, D., & Hemophilia Treatment Center Network. (2011). Range of motion measurements: Reference values and a database for comparison studies. Haemophilia, 17(3), 500–507. DOI: 10.1111/j.1365-2516.2010.02399.x
