The Knee Flexion Strength Test measures how much force a client can produce when bending the knee against resistance. It is commonly used to assess hamstring force output in a controlled isometric setup.

Knee flexion strength can provide useful context for walking, running, sprinting, deceleration, jumping, landing, change of direction, field sport, court sport, posterior-chain strength profiling and progress tracking. The main contributors include biceps femoris, semitendinosus and semimembranosus, with assistance from gastrocnemius and other muscles depending on knee angle, hip angle and foot position.

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 knee flexion testing, peak force is usually the main metric. Force as a percentage of body weight may be useful if directly calculated from the client’s test force and body weight, especially for baseline comparison, side-to-side comparison and retesting. Rate of force development and time to peak may be useful when rapid hamstring force production matters, such as sprinting, deceleration, landing or change of direction. Impulse may be useful if sustained knee flexion force over a defined time window is intentionally tested. Fatigue index is only relevant if repeated or sustained knee flexion efforts are part of the protocol.

The result can support assessment reasoning and progress tracking, but it does not diagnose hamstring strain, tendon injury, knee pathology, sciatic nerve involvement, posterior thigh pain, sprinting readiness or readiness for sport or work on its own.

What Is the Knee Flexion Strength Test?

The Knee Flexion Strength Test is an isometric lower-limb strength assessment where the client attempts to bend the knee into the Muscle Meter, strap or fixed setup without visible joint movement. The device is usually placed against the posterior lower leg, ankle or heel region.

The movement direction is knee flexion. The purpose of the test is to measure how much bending force the client can produce through the knee flexors in a specific position.

Consistent setup matters because hip position, knee angle, pelvis position, trunk position, device placement, lower-leg contact point, strap angle and client effort can all affect the result. This test measures force output in a specific setup. It does not fully measure sprinting ability, running mechanics, hamstring tissue capacity, endurance, eccentric strength, knee function or sport/work readiness on its own.

Step-by-Step Protocol / Practice

1. Prepare the client

Explain that the test measures how strongly they can bend the knee into the Muscle Meter. Record baseline symptoms, posterior thigh discomfort, knee symptoms, calf symptoms, hip symptoms, lower-back symptoms, fatigue, recent activity, sprint exposure, training load and confidence with maximal effort.

Use at least one submaximal practice trial so the client understands the direction of force and learns to build force smoothly.

2. Set the client position

Knee flexion can be tested prone, seated, supine or in a specific 90-90 position. The chosen setup should match the reason for testing and should be repeated exactly at retest.

Record:

• Prone, seated, supine, 90-90 or other position
• Test side
• Hip angle
• Knee angle
• Pelvis position
• Trunk position
• Foot and ankle position
• Device contact point
• Whether a strap or fixed anchor was used

Prone testing is common for straightforward hamstring testing. Seated testing can be practical and controlled. Supine or 90-90 testing may be chosen to match specific hamstring length or sport-related positions.

3. Set up the device or straps

For a handheld setup, the professional holds the Muscle Meter against the posterior lower leg, ankle or heel region while the client bends the knee into it. For stronger clients or improved repeatability, a strap-stabilised or fixed setup is often preferred.

If using a strap, record:

• Anchor point
• Strap angle
• Strap length
• Device position
• Limb position
• Whether any pre-tension was used
• Whether the anchor moved during testing

Push, pull, handheld and strap-stabilised scores should be recorded separately unless the protocol supports direct comparison.

4. Place the device, strap or handle

Place the Muscle Meter against the posterior lower leg, ankle or heel region depending on the chosen protocol. Use the same contact point at retest. Avoid uncomfortable pressure on bony or sensitive areas.

The client should pull into knee flexion, as if trying to bend the knee, while the device or strap resists movement.

5. Stabilise the position

Stabilise the thigh, pelvis and trunk so the client does not compensate with hip extension, hip flexion, pelvis rotation, trunk movement, ankle pushing or whole-body bracing.

The aim is controlled knee flexion force in the chosen position.

6. Give clear instructions

Use consistent instructions such as:

“Bend your knee into the device as hard as you can and hold.”
“Pull your heel toward you without moving the position.”
“Build up smoothly, then pull hard.”
“Keep your hip, pelvis and trunk still.”
“Keep breathing.”
“Tell me if you feel pain, cramping, tingling or anything unusual.”

Use the same wording at retest where possible.

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 uses the best trial or the average of recorded trials. Either approach may be used if it is applied consistently.

8. Identify invalid trials

Repeat or mark a trial as invalid if:

• The hip angle changes
• The knee angle changes before the effort
• The pelvis lifts or rotates
• The trunk leans or shifts
• The ankle pushes instead of knee flexion
• The device slips
• The strap or anchor moves
• Pain or cramping limits effort
• The client starts before the device is ready
• The client holds their breath excessively
• The professional cannot hold the device steady

9. Record symptoms

Record posterior thigh pain, cramping, knee symptoms, calf symptoms, hip symptoms, lower-back symptoms, paraesthesia, confidence, apprehension and symptom response after testing. Do not repeatedly test through high pain, worsening symptoms or severe cramping.

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

Why It Is Used

The Knee Flexion Strength Test is used to quantify hamstring and knee flexor force output in a repeatable setup. It may be useful for:

• Baseline hamstring strength assessment
• Side-to-side comparison
• Monitoring change over time
• Posterior-chain strength profiling
• Comparing hamstring and quadriceps strength where relevant
• Supporting sprinting, running and deceleration assessment reasoning
• Supporting jumping, change-of-direction and field sport assessment reasoning
• Fitness and performance progress tracking
• Workplace context where lifting, carrying, climbing or repeated lower-limb loading is relevant
• Client education

The test should support assessment reasoning. It should not be used as a stand-alone diagnostic or clearance measure.

What It Measures

The test primarily measures isometric knee flexion force output in the chosen setup. It reflects the client’s ability to produce hamstring and knee flexor force while maintaining the chosen hip, knee and pelvis position.

It may provide useful information about:

• Knee flexion force capacity
• Hamstring force contribution
• Side-to-side force difference
• Force relative to body weight, if calculated
• Confidence producing hamstring force
• Pain response during resisted knee flexion
• Change in force over time
• Relationship between strength and related movement tasks

It does not directly measure:

• Hamstring tissue healing
• Cause of posterior thigh pain
• Sciatic nerve involvement
• Knee joint pathology
• Sprinting mechanics
• Eccentric hamstring capacity
• Running readiness
• Sport or work readiness

Understanding the Result, Reference Values and What to Look For

What a higher or lower result may suggest

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

Lower force may be influenced by pain, apprehension, poor familiarisation, fatigue, guarding, cramping, inconsistent device placement, poor pelvis stabilisation, reduced confidence, recent sprint exposure, posterior thigh symptoms, knee symptoms or compensation from the hip or trunk.

One result should not be interpreted in isolation. Interpretation is strongest when the same setup is repeated over time and reviewed alongside symptoms, confidence, knee range, hip range, quadriceps strength, hip extension strength, running exposure, sprinting, jumping, deceleration and work-specific demands.

What can influence the result

Important influences include:

• Pain
• Apprehension
• Poor familiarisation
• Fatigue
• Cramping
• Guarding
• Hip angle
• Knee angle
• Pelvis position
• Trunk position
• Device placement
• Strap angle
• Lower-leg contact point
• Foot and ankle position
• Breath holding
• Client confidence
• Professional strength if using handheld resistance

Normative, reference and comparative values

Published Muscle Meter-specific universal norms for knee flexion are limited. Reference values should therefore be used as context only and not as direct targets unless the protocol is closely matched.

More user-friendly comparison data include:

• The original knee flexion article discussed broad isometric knee flexion values around 120–140 Nm for males and 70–90 Nm for females, but these are torque-based general values and are not direct Muscle Meter force targets.
• A systematic review of isometric knee extension and flexion strength found that reference values vary substantially by device, knee angle, hip angle, age, sex and test method. This supports using matched protocols and avoiding simple universal targets.
• For older adults, pooled mid-range knee flexion values have been reported around 0.69–0.89 Nm/kg for males and 0.46–0.81 Nm/kg for females. These values are useful background context but should not be converted into a pass/fail Muscle Meter target.
• For Muscle Meter testing, user-friendly interpretation is usually strongest when using the client’s own baseline, right-to-left comparison, percentage of body weight if calculated, symptoms and repeated testing under the same setup.
• For side-to-side comparison, a difference of around 10% or more is often worth reviewing more closely, especially if it matches symptoms, previous injury, confidence changes, sprint exposure or functional differences. This is not a strict pass/fail cut-off.
• If force is recorded as a percentage of body weight in Measurz, use it mainly for the client’s own baseline, side-to-side comparison and retesting. Bodyweight percentage is useful only when calculated from the client’s actual test force and body weight.
• If hamstring-to-quadriceps comparison is used, record the exact knee flexion and knee extension protocols because different joint angles can change the apparent ratio.

These values and comparisons are best used as context. They can help structure interpretation, 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. Review force relative to body weight where calculated.
4. Compare hamstring and quadriceps strength where relevant.
5. Consider symptoms during and after testing.
6. Consider confidence and effort quality.
7. Review whether compensations were present.
8. Compare with related strength, mobility or performance tests.
9. Relate the result to running, sprinting, jumping, sport, work or daily-life demands.
10. Retest under the same conditions to monitor change.
11. Do not use reference values as pass/fail criteria.

What to look at for each relevant Muscle Meter metric

Peak force
Use for maximum knee flexion force output, baseline strength, side-to-side 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 when calculated directly from test force and body weight. It may help compare the client’s result to their own baseline, the opposite side and body size. Do not treat it as a universal target unless the comparison data use a closely matched protocol.

Torque
Use only when the lever arm is measured and a more biomechanical interpretation is needed. It can help when lower-leg length or device placement changes the raw force reading. It should not be used as normative data unless the reference data match the setup closely.

Rate of force development
Use when rapid hamstring force matters, such as sprinting, deceleration, landing or change of direction. Look for early force production and whether rate of force development 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 knee flexion force briefly and whether impulse improves while peak force stays similar.

Fatigue index
Use only if repeated or sustained knee flexion 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, attention, training age and familiarisation. Practice trials are important because maximal hamstring effort can be difficult to coordinate without pelvis or trunk movement.

Adults and general fitness clients
Use the test for baseline hamstring strength, progress tracking and confidence with loading. Compare results with hip extension strength, quadriceps strength, lower-limb mobility and general exercise goals.

Older adults
Consider walking confidence, stairs, transfers, balance, fatigue, rest periods and function. A lower score may provide useful context, but it should not be interpreted without functional assessment.

Athletes and sport clients
Consider sprinting, running, deceleration, jumping, cutting and field or court sport demands. Peak force alone does not equal sport performance, but it can support a broader lower-limb strength profile.

Workplace and manual task clients
Consider lifting, carrying, stairs, ladders, uneven ground, walking distance and repeated lower-limb loading 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, not assumptions about body size.

Reliability, Validity and Measurement Considerations

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

• Same body position
• Same hip angle
• Same knee angle
• Same pelvis position
• Same trunk position
• Same lower-leg contact point
• 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 stabilisation
• Same instructions
• Same contraction duration
• Same rest period
• Same scoring method
• Same symptom and compensation recording

Knee flexion strength testing is setup-dependent. Small changes in hip angle, knee angle, lower-leg contact point or pelvis control can change the score. For stronger clients, handheld resistance may be limited by professional strength. Strap-stabilised or fixed setups can improve repeatability.

Common Errors and Limitations

Common errors include:

• Hip angle changing
• Knee angle changing before the effort
• Pelvis lifting or rotating
• Trunk leaning
• Foot or ankle pushing instead of knee flexion
• Device placement changing between trials
• Strap or anchor movement
• Breath holding
• Testing through high pain or cramping
• Comparing different knee angles directly
• Treating the score as a diagnosis

Limitations include:

• Testing is setup-dependent
• Manual resistance may be limited by professional strength
• Muscle Meter-specific universal norms may be limited
• Published knee flexion values vary by device, hip angle, knee angle and population
• Pain, fear or guarding can reduce force output
• Peak force does not measure eccentric hamstring capacity
• Strong symmetry does not automatically indicate readiness for sprinting, sport or work

Practical Applications

The Knee Flexion Strength Test may be useful for:

• Baseline hamstring strength assessment
• Side-to-side comparison
• Monitoring response to exercise or intervention
• Comparing hamstring and quadriceps strength where relevant
• Supporting sprinting, running and deceleration assessment reasoning
• Comparing with hip extension strength, jumping, sprint exposure and workload
• Sport and workplace strength profiling
• Client education
• Fitness and performance progress tracking

Ideas to Make the Result Better

If force is low on both sides, consider assessing hip extension strength, quadriceps strength, hamstring mobility, sprint exposure, recent workload and confidence with loading.

If one side is much lower, compare with symptoms, injury history, hip and knee mobility, sprinting, jumping, deceleration, single-leg tasks and work or sport demands.

If pain or cramping limits the result, record symptom location and review whether hip angle, knee angle, device placement or effort level needs modification.

If force is good but function is limited, compare with sprint exposure, deceleration, jumping, running tolerance, posterior-chain endurance, workload and task exposure.

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: Prone, seated, supine, 90-90 or selected knee flexion test position
Start position: Hip and knee position recorded
Joint or trunk angle: Record hip angle, knee angle, pelvis and trunk 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 if directly calculated
Attachment or device setup: Muscle Meter against posterior lower leg, ankle or heel region, with consistent contact point; strap-stabilised if used
Final score: Best trial or average of trials
Key retesting requirement: Same body position, hip angle, knee angle, device placement, instructions, contraction duration, rest and scoring method

FAQs

What does the Knee Flexion Strength Test measure?

It measures isometric knee flexion force output in a specific setup.

Which muscles contribute to knee flexion?

The main contributors are the hamstrings: biceps femoris, semitendinosus and semimembranosus. Gastrocnemius and other muscles may also contribute depending on knee angle, hip angle and foot position.

Should the result be recorded as percentage of body weight?

It can be if you calculate it directly from test force and body weight. This is useful for internal comparison, especially when tracking change over time.

Are there universal knee flexion norms for the Muscle Meter?

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

What numerical values are available for comparison?

Broad knee flexion reference data exist, but values vary by protocol. Older-adult review values include mid-range knee flexion around 0.69–0.89 Nm/kg for males and 0.46–0.81 Nm/kg for females, but these are torque-based background values rather than Muscle Meter force targets.

Can this test diagnose a hamstring injury?

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

What can make the result unreliable?

Changing hip angle, knee angle, pelvis position, device placement, pain, fatigue, cramping and inconsistent instructions can affect results.

What should be recorded in Measurz?

Record side, body position, hip angle, knee angle, device placement, peak force, percentage bodyweight if calculated, symptoms, compensations, confidence, scoring method and related findings.

Key Takeaways

• The Knee Flexion Strength Test measures isometric knee flexion force output.
• Peak force is usually the main routine Muscle Meter metric.
• Published knee flexion reference data vary by hip angle, knee angle, device and population.
• Percentage of body weight should only be used when calculated directly from force and body weight.
• Baseline comparison, side-to-side comparison and retesting consistency 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 calculated, compensations and retesting conditions.

References

Baron, M., Tousignant-Laflamme, Y., & Roy, J.-S. (2024). Validity and reliability of handheld dynamometry to assess isometric knee muscle strength in healthy adults. Journal of Sport Rehabilitation, 33(4), 267–276.

Bohannon, R. W. (1997). Reference values for extremity muscle strength obtained by hand-held dynamometry from adults aged 20 to 79 years. Archives of Physical Medicine and Rehabilitation, 78(1), 26–32. https://doi.org/10.1016/S0003-9993(97)90005-8

Marušič, J., Šarabon, N., & others. (2021). Establishing reference values for isometric knee extension and flexion strength. Frontiers in Physiology, 12, 767941. https://doi.org/10.3389/fphys.2021.767941

McKay, M. J., Baldwin, J. N., Ferreira, P., Simic, M., Vanicek, N., Burns, J., & 1000 Norms Project Consortium. (2017). Normative reference values for strength and flexibility of 1,000 children and adults. Neurology, 88(1), 36–43. https://doi.org/10.1212/WNL.0000000000003466

Opar, D. A., Piatkowski, T., Williams, M. D., & Shield, A. J. (2013). A novel device using the Nordic hamstring exercise to assess eccentric knee flexor strength: A reliability and retrospective injury study. Journal of Orthopaedic & Sports Physical Therapy, 43(9), 636–640. https://doi.org/10.2519/jospt.2013.4837