The Knee Flexion Test measures how far the knee can bend. It is useful for baseline assessment, side-to-side comparison, progress tracking, return-to-training context and monitoring pain or symptoms during movement.
Knee flexion range of motion is one of the most commonly recorded lower-limb mobility measures. It helps professionals understand how comfortably a client can bend the knee during tasks such as squatting, lunging, kneeling, cycling, running preparation and floor-based movement.
A knee flexion result is useful, but it does not explain the cause of a movement limitation on its own. Interpretation is stronger when ROM is compared with the other side, the client’s baseline, pain response, confidence, strength, function and related assessment findings.
Measures knee bending range, usually in degrees.
Can be assessed actively, passively or both.
Record side, position, pain score, symptoms and compensation.
Compare to baseline and the opposite side rather than relying on one universal “normal”.
Small changes may reflect measurement error unless the protocol is consistent.
The Knee Flexion Test measures the available range as the knee bends. It can be performed as:
Active ROM: the client bends the knee using their own effort.
Passive ROM: the professional assists the knee into flexion without the client actively producing the movement.
Active ROM gives information about movement control, comfort and available self-generated range. Passive ROM gives additional context about available joint and soft-tissue range when the client is relaxed.
The test is used to:
Establish a knee ROM baseline.
Compare left and right sides.
Track progress across sessions.
Monitor symptoms with movement.
Guide exercise selection and range exposure.
Add context for lower-limb strength, function and movement testing.
Support return-to-training planning, without being used as a stand-alone clearance measure.
The test measures knee flexion in the sagittal plane. The result is usually recorded in degrees using an inclinometer, goniometer or digital ROM tool.
It may be influenced by:
pain or apprehension
swelling or stiffness
quadriceps and anterior thigh mobility
hamstring or calf bulk
previous injury or surgery
warm-up and fatigue
testing position
examiner stabilisation
device placement
This test is useful for:
athletes returning to running, jumping, squatting or kneeling
general fitness clients with lower-limb mobility goals
older adults where knee bending affects stairs, sitting and transfers
post-injury or post-surgery monitoring where appropriate
performance professionals tracking mobility alongside strength and function
teams or businesses wanting repeatable ROM data
Firm plinth, floor mat or testing bench
Inclinometer, goniometer or digital ROM device
Measurz recording profile
Optional towel or bolster
Pain scale
Notes field for symptoms and compensations
Choose the test position. Supine is commonly used for assisted knee flexion. Prone may also be used but should be recorded separately because values are not directly interchangeable.
Explain the movement. Ask the client to bend the knee as far as comfortable.
Set the starting position. The hip and pelvis should stay controlled. Avoid allowing the pelvis to rotate or lift.
Active ROM. Ask the client to slide the heel toward the buttock or bend the knee as far as they can without forcing.
Passive ROM, if relevant. Gently assist knee flexion until the first firm end point, symptom limit or compensation.
Device placement. With a goniometer, align the axis near the lateral femoral epicondyle, the stationary arm with the greater trochanter and the moving arm with the lateral malleolus. With an inclinometer, keep placement consistent and record the method.
Ask what the client feels. Record pain score, symptom location, tightness, pressure, apprehension or any unusual response.
Record compensations. Watch for hip hiking, pelvic rotation, lumbar extension, foot gripping or the client lifting the hip.
Trials. Use one familiarisation trial and one to three recorded trials if precision is important.
Retest consistency. Use the same position, warm-up, device, landmarks, side order and instructions next time.
Stop the test if pain increases sharply, symptoms are unusual, the client cannot relax during passive testing, or the movement is not appropriate for their current status.
Record knee flexion in degrees. Higher values generally reflect more available knee bending range, while lower values show less available range in that test position.
Interpretation should include:
active ROM result
passive ROM result, if tested
left versus right comparison
pain score
symptom location
end-feel or limiting factor
compensation pattern
change from baseline
related strength and function findings
A lower knee flexion score does not explain the cause by itself. It may reflect pain, guarding, swelling, soft-tissue limitation, joint stiffness, strength control, confidence, body size or testing method.
Evidence level: Level 2 — closest available reference values.
Common reference values often place knee flexion around 135–150 degrees, depending on source, population and method. The CDC normal joint ROM study provides age- and sex-specific reference values for selected joints and highlights that ROM differs by age and sex rather than being one universal number.
Use reference values as context, not strict pass/fail criteria. Knee flexion needed for daily function may be less than maximal anatomical range, but sport, kneeling tasks and deep squatting may require greater flexion.
Practical interpretation should prioritise:
baseline comparison
side-to-side difference
whether active and passive ROM differ
pain and symptom response
task goals such as squat depth, kneeling or cycling
consistency across repeat sessions
Lower-limb ROM measurement reliability depends heavily on standardised positioning, landmarks, device placement and examiner consistency. A recent systematic review of lower-limb ROM measurement found that reliability varies across joints, tools and protocols, which supports the need for consistent measurement procedures.
Clinical goniometric and digital tools can be useful, but measurement error comes from the device, examiner and client. A 2023 study on common goniometric devices emphasised the importance of validity, reliability and acceptable measurement error when ROM data are used for decisions.
No single MDC or MCID should be applied to all knee flexion testing unless it matches the protocol, population and device. Small changes should be interpreted cautiously unless they are repeated, meaningful to the client and supported by consistent testing.
Sensitivity and specificity are not usually applicable to knee flexion ROM testing because this assessment measures movement range rather than identifying a condition on its own.
Common issues include:
inconsistent starting position
poor goniometer or inclinometer placement
measuring hip or pelvic compensation instead of knee flexion
comparing active ROM with passive ROM as if they are the same
ignoring pain or symptom response
using different warm-ups between sessions
assuming one “normal” value applies to every client
comparing values from supine and prone testing without noting the difference
Knee flexion ROM can help with:
baseline knee mobility testing
monitoring progress after irritation, injury or surgery when appropriate
tracking tolerance to squatting, kneeling and cycling
comparing active and passive mobility
guiding exercise range selection
supporting return-to-training decisions alongside strength, balance, confidence and functional testing
In Measurz, record:
test name: Knee Flexion ROM
side tested
active or passive ROM
score in degrees
device used
client position
pain score
symptom location
end-feel or limiting factor
compensations
comparison side
baseline score
best or average trial
related strength or function findings
retest date
Example note: “Right knee flexion AROM 128°, supine, inclinometer, pain 2/10 anterior knee, mild hip lift near end range. Left 138°. Retest in two weeks.”
Knee Extension Test
Knee Prone Heel-to-Butt Test
90/90 Active Knee Extension Test
Hip Flexion Test
Squat assessment
Lower-limb strength testing
What is normal knee flexion ROM?
Common reference values are often around 135–150 degrees, but values vary by age, sex, body size, activity history and testing method.
Should knee flexion be measured actively or passively?
Both can be useful. Active ROM shows what the client can produce independently, while passive ROM adds context about available range with assistance.
What does reduced knee flexion mean?
It shows less available knee bending in that test, but it does not explain the cause on its own.
How should knee flexion be tracked over time?
Use the same position, device, landmarks, warm-up and instructions, then compare with baseline, symptoms and function.
Knee flexion ROM is best interpreted with side-to-side and baseline comparison.
Active and passive ROM should be recorded separately.
Pain, symptoms and compensations are as important as the degree score.
Standardised testing improves confidence in progress tracking.
Centers for Disease Control and Prevention. (2023). Normal joint range of motion study. https://archive.cdc.gov/www_cdc_gov/ncbddd/jointrom/index.html
Kiatkulanusorn, S., Luangpon, N., Srijunto, W., Watechagit, S., Pitchayadejanant, K., Kuharat, S., Bég, O. A., & Suato, B. P. (2023). Analysis of the concurrent validity and reliability of five common clinical goniometric devices. Scientific Reports, 13, 20725. https://doi.org/10.1038/s41598-023-48344-6
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.
