Peak force is the highest force a client produces during a test. It is commonly used to assess maximal force capacity during strength assessments, isometric tests, force plate testing, handheld dynamometry, load cell testing, push-pull assessments and performance testing.
Peak force can be recorded in several units, including kilograms, pounds, Newtons, or as a value relative to body weight, such as percentage of body weight. The most important rule is to record the unit used by the device and keep the same device, setup, position and unit when retesting.
For health and fitness professionals, peak force is useful because it gives a clear, objective number that can help track strength capacity, side-to-side differences, exercise progress, recovery trends and performance development. However, peak force should never be interpreted on its own. It should be considered with pain, symptoms, confidence, body size, task demands, movement quality, sport or activity goals, and related metrics such as rate of force development, impulse, fatigue index and time to peak.
Peer-reviewed research supports the use of handheld dynamometry and fixed dynamometry for measuring isometric muscle strength, with evidence showing good to excellent reliability and validity for many lower-limb measures, particularly around the hip and knee when protocols are standardised.
Strength is one of the most important physical qualities for health, fitness, sport and daily function. But strength is often discussed in vague terms such as “weak”, “strong”, “stable”, “powerful” or “not activating properly”. Peak force gives professionals a more objective way to measure how much force a client can actually produce in a specific test.
In Measurz, peak force can help professionals record a baseline, compare left and right sides, monitor progress after exercise interventions, assess changes across training blocks, and educate clients using clear numbers rather than guesswork.
Peak force is not a diagnosis. It does not explain the cause of pain, confirm readiness, or prove that one exercise is working by itself. It is best used as one part of a broader assessment profile that also includes symptoms, movement, confidence, function, range of motion, training history and client goals.
Metric name: Peak Force
What it means: The highest force produced during a test
Common units: Kilograms, pounds, Newtons, kilograms-force, pounds-force, or percentage of body weight
Common testing methods: Handheld dynamometry, fixed dynamometry, force plates, load cells, cable-based devices and push-pull strength tests
Best use: Strength assessment, baseline testing, side-to-side comparison, progress tracking and client education
Key interpretation point: Higher peak force usually indicates greater maximal force capacity in that specific test position
Major limitation: Peak force does not show how quickly force was produced, how well force was sustained, or why the result changed
Best practice: Use the same test setup, same device, same position, same side, same instructions and same scoring method for retesting
Peak force is the highest force value recorded during a test.
If you are looking at a force-time graph, peak force is the highest point on the curve. It tells you the maximum amount of force the client produced during that trial.
Peak force may be measured during:
Isometric strength testing
Handheld dynamometry
Fixed dynamometry
Force plate testing
Load cell testing
Grip strength testing
Push or pull testing
Jump testing
Mid-thigh pull testing
Calf raise or plantar flexion testing
Hip, knee, ankle, shoulder or trunk strength testing
In isometric testing, the client produces force without visible joint movement. For example, they may push against a fixed strap, handheld dynamometer or immovable surface. Isometric testing is widely used because it can be easier to standardise than dynamic testing and can provide useful force-time variables such as peak force, rate of force development and impulse. A systematic review by Lum and colleagues found that isometric force-time characteristics, including peak force, can show relationships with dynamic performance, although the strength of those relationships depends on the test, population and performance task.
Peak force can be measured using different devices. Common options include:
Handheld dynamometer
Fixed dynamometer
Force plate
Load cell
Cable-based strength device
Grip dynamometer
Isokinetic dynamometer
Muscle Meter or similar force-measuring device
Depending on the device, peak force may be displayed in:
Kilograms, often shown as kg or kgf
Pounds, often shown as lb or lbf
Newtons, shown as N
Percentage of body weight, shown as %BW
Normalised force, such as N/kg
Many practical devices used in health and fitness settings display values in kilograms or pounds. This is useful for communication because clients often understand these units more easily. However, professionals should remember that force is technically measured in Newtons, while kilograms are a unit of mass. In applied testing, devices that display “kg” are usually presenting a practical force-equivalent value. The safest approach is to record exactly what the device displays and keep the same unit for retesting.
Peak force is used because it provides a clear measure of the client’s maximum force output in a specific test.
For health and fitness professionals, this can help answer practical questions such as:
How strong is the client in this position?
Is one side producing less force than the other?
Has strength improved after a training block?
Is the client’s force output appropriate for their goal?
Is pain, fear, fatigue or poor confidence limiting effort?
Is maximal force improving, even if symptoms or function are also changing?
Does the client have enough force capacity before progressing to harder exercises?
Peer-reviewed research supports handheld dynamometry as a useful method for quantifying isometric strength. Mentiplay and colleagues found that handheld dynamometry had good to excellent reliability and validity for many lower-limb muscle groups in healthy adults, particularly for proximal muscles such as the hip and knee.
Peak force measures maximum force capacity in a specific test.
It may provide context about:
Maximal strength
Isometric force capacity
Side-to-side differences
Training adaptation
Exercise progression
Recovery or readiness trends
Force capacity relative to body weight
Performance potential in tasks where strength matters
Peak force does not directly measure:
Power
Speed
Rate of force development
Endurance
Movement quality
Pain cause
Tissue status
Coordination
Skill
Confidence
Return-to-sport readiness
Overall fitness
This distinction matters. A client can have a high peak force but still move poorly, fatigue quickly, hesitate during rapid tasks, or experience symptoms during sport or daily activity.
Peak force is often used as a practical measure of strength, but they are not exactly the same thing.
Strength is a broad physical quality. It can involve different joints, speeds, positions, muscle actions and tasks.
Peak force is a measured output from a specific test.
For example:
A knee extension test measures peak force in a specific knee position.
A grip test measures peak force from the hand and forearm.
A mid-thigh pull measures whole-body force production in a specific pulling position.
A jump test may record peak vertical ground reaction force during movement.
So, peak force is best understood as:
“How much force did the client produce in this specific test, under these exact conditions?”
That is why test setup matters so much.
When reviewing a peak force result, look at more than the number.
Consider:
Was the test set up correctly?
Was the client familiar with the task?
Did they give maximal effort?
Was pain present?
Was there hesitation or guarding?
Was the result consistent across trials?
Was the same position used as last time?
Was the same device used?
Was the same side tested?
Was the same unit used?
Was the result absolute or relative to body weight?
Was the result compared with a useful baseline?
A single peak force score can be useful, but the trend over time is often more valuable.
A higher peak force usually indicates greater maximal force capacity in that test position.
This may suggest that the client can produce more force during that specific movement or assessment. It may reflect improved strength, better confidence, better familiarisation, reduced symptoms, improved effort or a more effective setup.
A lower peak force may suggest reduced force capacity, but it does not explain why.
Possible reasons include:
Reduced strength
Pain or symptom limitation
Fear or low confidence
Poor understanding of the test
Fatigue
Recent training load
Poor sleep
Inconsistent setup
Poor stabilisation
Submaximal effort
Device placement differences
Different joint angle or body position
This is why professionals should avoid saying, “This muscle is weak” based only on one number. A better interpretation is:
“This test showed lower peak force today compared with baseline. We should interpret that alongside symptoms, confidence, setup, effort and related assessments.”
Peak force can be very useful for client education. Many clients understand progress better when they can see a number changing over time.
For example:
“Your right side produced 32 kg last session and 38 kg today.”
“Your left side is currently producing about 82% of your right side.”
“Your peak force has improved, but your force still takes longer to build compared with your other side.”
“Your strength is improving, but we still need to see how it transfers to movement and function.”
This makes the assessment more objective and helps clients understand progress beyond pain scores or subjective feeling.
Peak force can be used at the start of a program to establish a baseline. This gives the professional a reference point for future comparison.
Example:
A client begins a lower-limb strength program. You test knee extension peak force, hip abduction peak force and calf peak force. These values become the baseline for retesting later.
Peak force is useful when comparing left and right sides.
Example:
A client produces:
Right side: 45 kg
Left side: 36 kg
The left side is producing 80% of the right side.
This may help identify an asymmetry worth monitoring. However, limb symmetry should not be treated as the only goal. Research in ACL reconstruction populations has shown that limb symmetry can overestimate recovery if both limbs are weaker than expected, which means comparison with age-, sex- and activity-matched values may sometimes provide better context.
Peak force can support decisions about when to progress load, complexity or intensity.
For example:
Low peak force and high symptoms may suggest staying with lower-load options.
Improving peak force with stable symptoms may support gradual progression.
Strong peak force but poor control may suggest the client needs movement or coordination work as well.
Peak force does not prescribe the exercise, but it can support professional reasoning.
Peak force can show whether a training block is improving maximal force capacity.
Example:
A client completes six weeks of progressive strength training. Their hip extension peak force improves from 42 kg to 55 kg. This suggests improved force capacity in that specific test, especially if the setup, device and protocol were consistent.
A sudden reduction in peak force may suggest fatigue, poor recovery, soreness, symptoms, poor sleep or low effort.
This does not automatically mean something is wrong. It means the professional should look at the full picture:
Sleep
Stress
Training load
Symptoms
Soreness
Warm-up
Motivation
Recent illness
Other performance measures
Peak force can help track whether force capacity is improving during return-to-running, return-to-gym or return-to-sport progressions.
For example, recent research has explored isometric mid-thigh pull peak force and symmetry during phases after anterior cruciate ligament reconstruction, showing that peak force and asymmetry can change across rehabilitation phases and may provide useful progress information when interpreted with other measures.
Objective numbers can be motivating.
A client may feel like they are not improving because symptoms fluctuate, but peak force testing may show that they are producing more force over time. This can support education and confidence, provided the data is explained safely and not over-interpreted.
For general fitness clients, peak force can help track strength progress. It is especially useful when the client is following a structured program and wants to see whether strength capacity is improving.
For this group, interpretation should focus on:
Baseline comparison
Progress over time
Exercise tolerance
Confidence
Side-to-side comparison
Functional goals
Avoid comparing general fitness clients to athlete norms unless the protocol and population are clearly relevant.
For athletes, peak force can be useful for profiling maximal force capacity, monitoring training adaptation and identifying side-to-side differences.
However, sport performance is not determined by peak force alone. Rapid force production, impulse, power, technical skill, repeated effort ability and sport-specific decision-making also matter. Systematic review evidence suggests that isometric force-time variables can relate to dynamic performance, but these relationships vary depending on the task and testing method.
For athletes, peak force should usually be interpreted with:
Rate of force development
Impulse
Jump or sprint metrics
Limb symmetry
Training load
Sport demands
Fatigue state
In older adults, strength measures can provide important context for function, mobility and physical capacity. Muscle strength is often associated with physical performance, but the relationship depends on the strength measure, population and functional task. A review of clinical older populations found that strength measures are commonly studied in relation to motor function, although clinical usefulness depends on the measure and setting.
For older adults, peak force may be useful for tracking:
Lower-limb force capacity
Functional strength changes
Progress after resistance training
Side-to-side differences
Confidence with activity
Capacity for tasks such as standing, stepping or stair use
However, peak force should be interpreted alongside balance, gait, endurance, confidence, symptoms and daily function.
For clients with pain, peak force can help monitor how much force they are willing and able to produce in a controlled test.
A lower score may reflect true strength loss, but it may also reflect pain, fear, protective guarding, low confidence or poor tolerance. This is why the result should be recorded with pain score, symptoms and client feedback.
For example:
Peak force improved and pain stayed stable: may suggest improved tolerance.
Peak force dropped and pain increased: may suggest the session should be modified or reassessed.
Peak force stayed the same but confidence improved: still clinically useful information.
Use safe wording:
“This may indicate reduced force output in this test today.”
Avoid unsupported wording:
“This proves the muscle is inhibited.”
For clients returning after injury, peak force can support progress tracking, but it should not be used alone to clear participation.
Peak force may help monitor:
Side-to-side differences
Strength restoration
Response to loading
Progress across phases
Confidence with force production
In ACL reconstruction research, quadriceps strength and limb symmetry are commonly used, but limb symmetry alone may overestimate recovery because the uninvolved side may also lose strength. This supports using a broader comparison strategy rather than relying on one symmetry number.
For youth clients, peak force should be interpreted carefully because growth, maturation, coordination, body size and training age can all influence results.
A change in peak force may reflect:
Growth
Improved coordination
Familiarity with testing
Increased body mass
Strength adaptation
Better confidence
For youth, normalising to body weight can be useful, but it does not remove all growth and maturation effects.
Absolute peak force may be higher in larger clients simply because they have more mass or muscle mass. This is where relative force values can help.
For example:
Client A produces 80 kg peak force and weighs 80 kg.
Client B produces 80 kg peak force and weighs 120 kg.
Both have the same absolute peak force, but different relative force compared with body weight.
This is why body weight percentage can be useful for interpreting how much force a client produces relative to the body they need to move.
Research on strength normalisation supports scaling strength to body weight because it can reduce variability between people with different body sizes and make comparisons more meaningful.
Sometimes normative data or benchmark values are reported as percentage of body weight.
This means the client’s force output is expressed relative to their own body weight.
If peak force is recorded as 100% body weight, the client produced force equal to their body weight.
If peak force is recorded as 150% body weight, the client produced force equal to one and a half times their body weight.
If peak force is recorded as 200% body weight, the client produced force equal to twice their body weight.
Percentage body weight helps professionals compare force output between clients of different body sizes.
For example:
A 60 kg client producing 60 kg of force = 100% body weight.
A 100 kg client producing 60 kg of force = 60% body weight.
The absolute result is the same, but the relative result is very different.
If your device displays kilograms:
Peak force ÷ body mass × 100 = percentage body weight
Example:
Peak force: 45 kg
Body mass: 75 kg
45 ÷ 75 × 100 = 60% body weight
If your device displays pounds:
Peak force in pounds ÷ body weight in pounds × 100 = percentage body weight
Example:
Peak force: 120 lb
Body weight: 160 lb
120 ÷ 160 × 100 = 75% body weight
If your device displays Newtons, body weight should also be converted into Newtons before calculating percentage body weight.
Percentage body weight does not mean “good” or “bad” by itself.
It must be interpreted with:
Test type
Body region
Position
Side tested
Population
Device
Protocol
Normative source
Client goal
Symptoms
Related assessments
A value that is strong for one test may be low for another. For example, percentage body weight values for hip abduction cannot be compared with percentage body weight values for isometric mid-thigh pull.
A common mistake is comparing a client’s percentage body weight score to normative data from a different test.
For example:
Comparing knee extension peak force norms to hip abduction results
Comparing athlete norms to general population clients
Comparing force plate values to handheld dynamometry values
Comparing Newton-based values to kg-based values without proper conversion
Only compare values when the test, protocol, device, body region, units and population match closely.
Peak force normative data can be useful, but only when the comparison is appropriate.
Published reference values exist for some muscle groups, devices and populations. For example, Bohannon provided reference values for extremity muscle strength using handheld dynamometry in adults aged 20 to 79 years, showing that age, sex and body weight are important considerations when interpreting strength values.
However, a scoping review of reference values for maximal isometric muscle strength measured with handheld dynamometry found gaps in the available literature, meaning that reference values are not equally available for all muscle groups, age groups, devices or protocols.
For Measurz, the safest comparison options are:
Client baseline
Side-to-side comparison
Body weight percentage
Age-, sex- and activity-matched norms where available
Internal business or team benchmarks
Repeated testing under the same protocol
Related movement, function and symptom findings
Avoid using generic “normal” values unless the source clearly matches the client and test.
Not always. A higher peak force can be useful, but performance also depends on timing, coordination, speed, skill, endurance, movement quality and task specificity.
It does not. Peak force may show reduced force output, but it does not explain whether that is due to pain, confidence, strength, fatigue, fear, tissue sensitivity or testing setup.
Limb symmetry is useful, but it can be misleading. If both limbs are weak, symmetry may look good even though overall force capacity is low. Research after ACL reconstruction has shown that limb symmetry can overestimate quadriceps strength recovery, supporting the use of matched comparison data where available.
One peak force test gives one piece of information. Better interpretation comes from repeated trials, repeated sessions and comparison with related tests.
They should not be mixed without correct conversion. If your device records in kilograms, keep using kilograms for that client’s retesting unless you have a clear conversion process.
Peak force and power are different. Peak force measures maximum force. Power includes force and velocity. A client can be strong but not powerful if they produce force slowly.
Peak force is useful, but it has limitations.
It can be affected by:
Device type
Device placement
Stabilisation
Joint angle
Lever arm
Client position
Instructions
Warm-up
Familiarisation
Pain
Fatigue
Sleep
Motivation
Confidence
Assessor strength when using handheld devices
Whether the test is make-style or break-style
Handheld dynamometry can be reliable, but assessor strength and stabilisation can influence results. Fixed dynamometry or external fixation may improve consistency for stronger clients or higher force tests. Research comparing handheld and fixed dynamometry supports the use of dynamometry for objective strength measurement, but also shows that reliability and validity can vary by muscle group and testing setup.
To improve the quality of peak force data:
Use the same device each time.
Use the same unit each time.
Standardise the client’s position.
Record the joint angle.
Use the same attachment or contact point.
Stabilise the client well.
Provide clear instructions.
Allow familiarisation trials.
Record multiple trials.
Use the same scoring method, such as best trial or average.
Record pain and symptoms.
Record effort and confidence.
Retest under similar conditions.
The more consistent the protocol, the more meaningful the comparison.
Record:
Metric: Peak Force
Score/result: highest force recorded
Units: kilograms, pounds, Newtons, kgf, lbf, N/kg or percentage body weight
Test name: for example, knee extension, hip abduction, grip strength or isometric mid-thigh pull
Side: left, right or bilateral
Dominance: dominant or non-dominant side
Position: seated, standing, supine, prone or sport-specific position
Joint angle: if relevant
Device used: handheld dynamometer, fixed dynamometer, force plate, load cell or Muscle Meter
Attachment or placement: where the device was positioned
Trial number: trial 1, trial 2, trial 3
Final score method: best score or average score
Body mass: if calculating percentage body weight
Pain score: before, during or after testing
Symptoms: pain, apprehension, fatigue, cramping or none
Compensations: trunk lean, gripping, bracing, breath-holding, poor position or movement
Effort quality: maximal, submaximal, hesitant or unclear
Baseline comparison: previous result
Retest date: planned follow-up
Related findings: RFD, impulse, torque, fatigue index, movement assessment or functional test
Measurz should be used to support measurement, comparison, monitoring, education and progress tracking. Peak force should not be positioned as diagnosing a condition or confirming readiness on its own.
A client begins a strength program and records a hip abduction peak force of 22 kg on the right and 19 kg on the left. After eight weeks, the results improve to 28 kg and 26 kg.
This suggests improved force capacity in that test. It may also support client motivation because progress is visible.
A runner has good calf peak force but poor rate of force development. This suggests they can produce force, but may be slower to access it quickly. Peak force alone would miss this detail.
An older adult improves sit-to-stand performance and knee extension peak force over a 10-week strengthening program. The combined improvement may provide stronger evidence of functional progress than either measure alone.
A client has 95% limb symmetry, but both limbs are below expected values for their sport and body size. This is why symmetry alone can be misleading.
A client produces 70 kg of peak force and weighs 140 kg. Their result is 50% body weight. Another client produces 70 kg and weighs 70 kg. Their result is 100% body weight. The same absolute force has different meaning when body mass is considered.
Peak force is the highest force produced during a test. It shows the maximum force output recorded in that specific assessment.
It can be. Many practical devices display peak force in kilograms or pounds. Other devices may display Newtons, kgf, lbf, N/kg or percentage body weight. Record the exact unit shown by the device.
Peak force is one way to measure strength in a specific test. Strength is broader and depends on the task, joint angle, movement, speed, position and context.
Not always. Higher peak force may be useful, but it must be interpreted with body mass, symptoms, movement quality, sport demands, function and other performance metrics.
It means the force output is expressed relative to the client’s body weight. For example, 100% body weight means the client produced force equal to their body weight. This can make comparison more meaningful between clients of different sizes.
If the device displays kilograms:
Peak force in kg ÷ body mass in kg × 100
If the device displays pounds:
Peak force in lb ÷ body weight in lb × 100
Use the same unit for force and body weight.
Only if the test, device, setup, body region, units and population are similar. Otherwise, compare the client to their own baseline.
Multiple trials are preferred. Many professionals record two to three trials and use either the best score or the average, but the method should be consistent across retests.
That may suggest improved force capacity, but it does not explain pain. Interpret the result with symptoms, function, movement quality and client goals.
A decrease may reflect fatigue, pain, poor sleep, stress, reduced confidence, recent exercise, low effort or a real reduction in force capacity. Repeat testing and context are important.
No. Peak force is useful, but it should be interpreted with related assessments and professional reasoning.
Peak force is the highest force produced during a test.
It can be measured in kilograms, pounds, Newtons or relative to body weight.
Peak force is useful for baseline testing, side-to-side comparison, progress tracking and client education.
Percentage body weight helps interpret force relative to body size.
Normative data should only be used when the protocol, device, population and units match.
Peak force does not explain pain, power, speed, endurance or movement quality by itself.
Measurz should record peak force with context so retesting is meaningful.
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.
Kuenze, C. M., Blemker, S. S., & Hart, J. M. (2021). Quadriceps strength after anterior cruciate ligament reconstruction may overestimate recovery when using limb symmetry. Orthopaedic Journal of Sports Medicine, 9(2).
Lum, D., Haff, G. G., & Barbosa, T. M. (2020). The relationship between isometric force-time characteristics and dynamic performance: A systematic review. Sports, 8(5), Article 63.
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), Article e0140822.
Morton, S. M., Whitehead, J. R., Brinkert, R. H., & Caine, D. J. (2011). Resistance training vs. static stretching: Effects on flexibility and strength. Journal of Strength and Conditioning Research, 25(12), 3391–3398.
Stofberg, J. P., Aginsky, K., van Aswegen, M., & Kramer, M. (2024). Changes in isometric mid-thigh pull peak force and symmetry across anterior cruciate ligament reconstruction rehabilitation phases. Frontiers in Rehabilitation Sciences, 5, Article 1418270.
Vila, H., Teixeira, A. M., Figueiredo, P., & Fernandes, R. J. (2021). The effects of anthropometric scaling parameters on normalised muscle strength in untrained adults. Sports Medicine - Open, 7, Article 75.
