Rate of Force Development, commonly abbreviated as RFD, measures how quickly force is produced. It is one of the most useful force-time metrics when a professional wants to understand not only how much force a client can produce, but how fast they can produce it.
Peak force tells you the highest force reached. RFD tells you how quickly force rises.
This matters because many real-world activities happen quickly. Sprinting, jumping, landing, stepping, changing direction, recovering balance and reacting to sport demands often require force to be produced in a short time window. A client may have good peak force, but if they produce that force too slowly, it may not be useful for faster tasks.
A high RFD generally suggests the client can produce force quickly in the tested task. A low RFD may suggest slower rapid force production, but it may also reflect pain, hesitation, fatigue, low confidence, poor instructions, unfamiliarity with the test, inconsistent setup or data-processing differences.
RFD is commonly used to characterise explosive strength in athletes, older adults and clinical populations, but peer-reviewed methodological reviews emphasise that RFD is highly sensitive to testing and analysis methods, so careful protocol control is essential.
A client can be strong but slow.
That means they may be able to produce a high peak force if given enough time, but they may struggle to access that force quickly. For some clients, that may not matter much. For others, especially athletes, runners, older adults, and clients returning to dynamic activity, the speed of force production can be highly relevant.
Rate of Force Development helps answer:
“How quickly can this client produce force?”
In Measurz, RFD can help professionals monitor explosive strength qualities, compare sides, track progress across exercise blocks, identify differences between maximal strength and rapid force production, and educate clients about why “strength” and “fast force” are not the same thing.
RFD should not be used as a diagnosis, clearance test or standalone decision-maker. It is most useful when interpreted with peak force, impulse, time to peak, symptoms, movement quality, fatigue response, task demands and the client’s goals.
Metric name: Rate of Force Development
Common abbreviation: RFD
What it means: How quickly force is produced
Simple formula: Change in force ÷ change in time
Common units: N/s or N·s⁻¹
Other possible units: kg/s, kgf/s, lb/s, lbf/s or device-specific force-time units
Common testing methods: Isometric force testing, force plates, load cells, handheld dynamometry, fixed dynamometry, push-pull tests and jump testing
Best use: Explosive strength profiling, side-to-side comparison, monitoring rapid force production, tracking training response and identifying differences between peak force and fast force output
High RFD: Usually indicates faster force production in the tested task
Low RFD: Usually indicates slower force production, but the reason must be interpreted with context
Major limitation: RFD is highly sensitive to start threshold, sampling rate, filtering, time window, instructions and client familiarity
Rate of Force Development measures the speed at which force increases.
A simple way to explain it:
Peak force = how much force was eventually produced.
RFD = how quickly force was produced.
If you are looking at a force-time graph, RFD is related to the steepness of the force curve. A steep curve means force increased quickly. A flatter curve means force increased more slowly.
RFD = change in force ÷ change in time
For example:
Force increases from 0 N to 600 N
Time taken = 0.20 seconds
RFD = 600 ÷ 0.20
RFD = 3000 N/s
This means the client developed force at a rate of 3000 newtons per second over that time window.
RFD is calculated from a force-time curve.
A force-time curve shows how force changes from the start of a contraction or movement through to the end of the test.
RFD can be measured during:
Isometric strength testing
Isometric mid-thigh pull
Isometric squat
Push or pull testing
Handheld or fixed dynamometry
Force plate testing
Jump testing
Grip testing
Load cell testing
Muscle Meter-style force testing
Common units include:
N/s
N·s⁻¹
kg/s, when the device displays force in kilograms
kgf/s, when the device displays kilograms-force
lb/s or lbf/s, when the device displays force in pounds
The safest approach is to record the exact unit shown by the device and use the same device, unit, test, time window and calculation method for retesting.
RFD is used because many tasks happen before a client has time to reach peak force.
For example:
A sprint ground contact may be too short for the client to reach maximum force.
A jump take-off requires rapid force production.
A landing or cutting task requires quick force acceptance and redirection.
A balance recovery step may require fast lower-limb force production.
A sport contact or reaction task may require rapid bracing or pushing.
In these situations, the ability to produce force quickly may be more relevant than maximum force alone.
A systematic review of multi-joint isometric testing found that peak force, RFD and impulse can show relationships with dynamic performance, but the strength of those relationships varies depending on the test and performance task. This supports using RFD as part of a broader assessment profile rather than as a universal performance score.
RFD measures rapid force production.
It may provide context about:
Explosive strength
Rapid neuromuscular output
Early force contribution
Fast strength expression
Side-to-side differences
Force-time strategy
Fatigue-related slowing
Response to rapid-intent training
Performance in time-limited tasks
Readiness to progress toward faster exercise tasks
RFD does not directly measure:
Peak strength
Muscle size
Tissue status
Pain source
Movement quality
Coordination
Balance
Overall fitness
Injury risk on its own
Readiness to return to sport
RFD is a useful metric, but it does not explain why the result changed. It must be interpreted with context.
RFD can be calculated in several ways. These methods are not interchangeable, so the time window and calculation method must always be recorded.
Early RFD is calculated during the first part of the contraction, commonly within time windows such as:
0–50 ms
0–100 ms
0–200 ms
Early RFD may be especially relevant for tasks that require force very quickly, such as sprinting, landing, stepping or reacting. However, early RFD is also more sensitive to noise, start threshold and measurement error.
Late RFD is calculated over a later period, such as:
100–200 ms
100–300 ms
200–300 ms
Late RFD may be more influenced by maximal strength capacity, depending on the test and client population.
Peak RFD is the highest rate of force rise recorded during the contraction.
It can be useful, but it is also sensitive to signal noise, filtering and device sampling rate. Methodological research shows that filtering and starting-force threshold can substantially affect RFD values and reliability.
Average RFD is calculated across a defined time window.
This is often easier to interpret than peak RFD because the time window is clear.
Relative RFD expresses rapid force production relative to body mass or peak force.
Examples include:
N/s/kg
N·s⁻¹·kg⁻¹
RFD relative to peak force
Relative RFD can help when comparing people of different body sizes or understanding how quickly a client accesses their own maximal force capacity.
RFD and peak force answer different questions.
Peak force asks:
“How much force can the client produce?”
RFD asks:
“How quickly can the client produce force?”
A client can have:
High peak force and high RFD
High peak force and low RFD
Low peak force and high early RFD
Low peak force and low RFD
This is why RFD should be interpreted with peak force, not instead of it.
A client may produce 100 kg peak force in an isometric test, but take a long time to reach it.
Another client may produce 80 kg peak force, but produce force much faster in the first 100–200 ms.
Which profile is better depends on the client’s goal. For slow strength tasks, peak force may be more important. For sprinting, jumping, landing or reacting, RFD may add useful context.
RFD and impulse also tell different stories.
RFD asks:
“How quickly did force rise?”
Impulse asks:
“How much force was applied across time?”
A client may have high RFD but low impulse if they produce force quickly but do not sustain it.
Another client may have lower RFD but higher impulse if they produce force more gradually and maintain it longer.
Both can be useful. RFD explains the speed of force production. Impulse explains total force-time contribution.
RFD and Time to Peak are related but different.
RFD asks:
“How steeply did force rise?”
Time to Peak asks:
“How long did it take to reach the highest force?”
A client may have:
High RFD and short time to peak
High peak force but long time to peak
Low RFD and long time to peak
High early RFD but lower peak force
Using RFD with Time to Peak can help professionals understand the client’s force-time strategy.
A high RFD usually means the client produced force quickly during the tested task.
This may suggest:
Faster force production
Better explosive strength expression
Stronger early force contribution
Greater ability to access force quickly
Better performance potential in time-limited tasks
Positive adaptation to rapid-intent or explosive training
Better neuromuscular readiness in that specific test context
High RFD may be a positive finding when:
It improves under the same protocol
Peak force is maintained or improved
Symptoms remain stable or improve
Movement quality remains acceptable
It aligns with better jump, sprint, balance or function outcomes
The client’s goal requires fast force production
However, high RFD is not automatically better in every setting.
A high RFD may be less meaningful if:
The test was noisy
Start detection was inconsistent
The client pre-tensioned before the test
The device sampling rate was too low
The value came from one inconsistent trial
The client sacrificed peak force or movement quality
The client’s goal does not require rapid force production
“RFD was higher in this test, suggesting faster force production under this protocol. This should be interpreted with peak force, symptoms, movement quality, time window and task demands.”
A low RFD usually means the client developed force more slowly during the tested task.
This may suggest:
Slower rapid force production
Reduced explosive strength expression
Lower early force contribution
Pain-related hesitation
Apprehension or low confidence
Fatigue
Poor familiarisation
Reduced peak force capacity
Poor instructions
Inconsistent start point
Poor test setup
Lower intent during the trial
Low RFD does not automatically mean the client is weak. A client may have good peak force but still produce force slowly.
Low RFD may be meaningful when:
It is consistently lower than baseline
It is lower on one side
It occurs with slower movement performance
It occurs with increased symptoms or apprehension
It aligns with poor early impulse or longer time to peak
It is relevant to the client’s sport, fitness or function goal
Low RFD may be less meaningful when:
The test was not intended to be explosive
The client did not understand the instruction
Only one trial was recorded
The start threshold changed
The device or software changed
The client was guarding due to discomfort
“RFD was lower in this test today, which may indicate slower force production across the measured time window. This should be interpreted with peak force, baseline, symptoms, test quality and task goals.”
RFD is useful for helping clients understand that force production has a timing component.
You might say:
“Peak force tells us how much force you can produce. RFD tells us how quickly you can access that force.”
This can be especially helpful for clients who are strong in slow exercises but struggle with faster movement tasks.
RFD can help monitor whether training is improving rapid force production.
This may be relevant for:
Sprinting
Jumping
Landing
Cutting
Rapid stepping
Balance recovery
Sport contact
High-speed gym-based movements
RFD may reveal side-to-side differences that peak force alone does not.
For example:
Right and left peak force may be similar.
One side may show slower early RFD.
This may suggest that both sides can eventually produce similar force, but one side accesses force more slowly.
RFD may improve after training that emphasises rapid intent, explosive actions or high-speed strength work.
However, RFD should be interpreted alongside peak force. If RFD improves but peak force drops, the meaning may be different from a case where both improve.
A sudden drop in RFD may reflect fatigue, soreness, poor sleep, low motivation, pain or poor recovery. It should not automatically be treated as a problem, but it may be a useful conversation starter.
RFD may help guide progression from slow controlled force production toward faster tasks.
For example:
Low peak force and low RFD may suggest a need to build base strength first.
Good peak force but low RFD may suggest adding rapid-intent work when appropriate.
Improving RFD with stable symptoms may support progression to faster movements, depending on movement quality and goals.
For general fitness clients, RFD is usually more advanced than peak force. Many clients will benefit first from tracking peak force, consistency, movement quality and exercise tolerance.
RFD becomes more useful when goals include:
Running
Jumping
Agility
Faster lifting
Athletic development
Dynamic exercise progression
Improving quick reactions
Use RFD mainly as a trend metric rather than a pass/fail score.
For athletes, RFD is highly relevant because many sport actions occur in short time windows.
Examples include:
Sprint acceleration
Jump take-off
Change of direction
Landing
Tackling or contact preparation
Throwing
Kicking
Rapid deceleration
The major review by Maffiuletti and colleagues describes RFD as a commonly used measure for characterising explosive strength in athletes, older individuals and clinical populations, while emphasising that its assessment requires careful methodological control.
For athletes, RFD should be interpreted with:
Peak force
Impulse
Time to peak
Jump or sprint performance
Training load
Fatigue state
Symptoms
Sport demands
For older adults, rapid force production may matter because many balance and functional tasks require force to be produced quickly.
Recent research on falls and lower-limb strength notes that lower-limb power and rapid force or torque development are affected by ageing and may be relevant to maintaining postural balance, although findings about falls associations can be inconsistent across studies.
For older adults, RFD should be interpreted with:
Balance
Gait
Sit-to-stand performance
Step speed
Confidence
Fear of falling
Lower-limb strength
Symptoms
Daily function
RFD may be useful, but it should not replace practical functional testing.
For clients with pain, RFD can be affected by discomfort, apprehension or protective strategy.
Low RFD may reflect:
Pain-related hesitation
Guarding
Reduced confidence
Fear of fast effort
Reduced force capacity
Fatigue
Poor familiarisation
Test discomfort
Record symptoms and pain score every time. Avoid saying low RFD proves inhibition or damage.
Use safer wording:
“This result may suggest slower force production during this test today.”
RFD can provide useful context during return-to-performance monitoring because rapid force production may remain limited even when peak force improves.
For example:
Peak force may return before early RFD improves.
One side may show similar peak force but slower force development.
Time to peak may remain longer even when maximal force looks acceptable.
RFD should support monitoring, not standalone clearance.
For youth clients, RFD should be interpreted carefully because growth, maturation, coordination and test familiarity can strongly affect rapid force production.
Changes may reflect:
Growth
Maturation
Improved coordination
Better understanding of the test
Increased body mass
Training adaptation
Better confidence
Use youth-specific reference data only when available for the exact protocol. Otherwise, use baseline and repeat testing.
For higher body mass clients, absolute RFD may be high, but relative RFD may provide better context for bodyweight tasks.
If the client needs to move their own body quickly, such as during stepping, running, jumping or balance recovery, body-mass-normalised RFD may be useful.
However, relative values still need careful interpretation because body composition, limb length, training history and test familiarity all influence results.
RFD can be reported in several relative ways.
This may be expressed as:
N/s/kg
N·s⁻¹·kg⁻¹
This helps answer:
“How quickly is the client producing force relative to their body size?”
This can be useful for bodyweight tasks such as running, jumping, stepping and balance recovery.
This helps answer:
“How quickly does the client access their own maximum force capacity?”
For example, two clients may have different peak force values, but one may reach a higher percentage of their maximum force earlier in the contraction.
Relative RFD can be useful, but it does not remove all differences related to:
Age
Sex
Body composition
Limb length
Training history
Pain
Motivation
Familiarity
Device method
Protocol
Use the same calculation method across sessions.
No. There are no true universal RFD norms that apply across all tests, devices, clients and populations.
RFD values depend on:
Test type
Device
Sampling rate
Filtering
Start threshold
Time window
Body position
Joint angle
Instructions
Familiarisation
Muscle group or task
Whether the value is peak, early, late or average RFD
Whether the value is absolute or normalised
Age
Sex
Training history
Symptoms
Because RFD is sensitive to testing and analysis methods, universal norms are not appropriate.
The strongest evidence supports using RFD as a protocol-specific trend and comparison metric.
Maffiuletti and colleagues emphasise that RFD is useful for characterising explosive strength, but methodological choices such as instructions, signal processing, contraction onset and calculation method strongly influence results.
Lum and colleagues reviewed multi-joint isometric force-time characteristics and found that RFD, peak force and impulse can relate to dynamic performance, but results vary by task and protocol. This supports using RFD with matched testing methods rather than generic norms.
Moir and colleagues showed that filtering and starting-force thresholds can change RFD values and reliability during isometric back squat testing, reinforcing that RFD interpretation depends heavily on processing method.
For most professional settings, interpret RFD using:
Client baseline
Side-to-side comparison
Same test, same device and same protocol
Time-window-specific comparison
Body-mass-normalised values where relevant
Published reference data only when the protocol and population match
Related measures such as peak force, impulse, time to peak and functional performance
Published RFD data may be useful only when they match:
Same test
Same device
Same time window
Same start threshold
Same filtering method
Same population
Same units
Same contraction instruction
If these details do not match, published values should be treated as broad context, not strict benchmarks.
No. RFD measures how quickly force is produced. Peak force measures how much force is produced.
Not always. High RFD is useful when the task requires rapid force production. It may be less relevant for slower strength or endurance tasks.
No. Low RFD may reflect slow force production, but it can also reflect pain, hesitation, fatigue, low confidence, poor familiarisation or measurement differences.
Not safely unless the device, sampling rate, filtering and calculation method are comparable.
They are not. Early RFD, late RFD, average RFD and peak RFD may tell different stories.
No. RFD is highly protocol-specific and should be interpreted using matched reference data or repeated testing.
RFD is useful but sensitive.
It can be affected by:
Device type
Sampling rate
Filtering
Start threshold
Contraction onset detection
Time window
Joint angle
Body position
Stabilisation
Instructions
Pre-tension
Countermovement
Familiarisation
Pain
Fatigue
Motivation
Effort
Test anxiety
Assessor technique
The most important limitation is that small methodological changes can meaningfully change RFD. This makes RFD less forgiving than peak force.
Where possible, use RFD as a trend metric under tightly standardised conditions.
To improve RFD data quality:
Use the same device each time.
Use the same body position.
Use the same joint angle where relevant.
Use the same instructions.
Use clear explosive intent cues.
Avoid pre-tension unless it is part of the protocol.
Use familiarisation trials.
Record multiple trials.
Use the same time window.
Use the same start threshold.
Use the same filtering method.
Use the same scoring method.
Record symptoms and pain.
Record body mass if normalising.
Interpret RFD with peak force and task demands.
A practical instruction is:
“Push as fast and as hard as possible.”
This is different from:
“Push as hard as possible.”
The first instruction emphasises rapid force production. The second may produce a slower ramp and reduce RFD relevance.
Record:
Metric: Rate of Force Development
Score/result: RFD value
Units: N/s, kg/s, kgf/s, lb/s, lbf/s or device-specific unit
RFD type: early RFD, late RFD, peak RFD, average RFD or relative RFD
Time window: for example, 0–50 ms, 0–100 ms, 0–200 ms or 100–200 ms
Test name: isometric push, pull, squat, grip, mid-thigh pull, jump or other force test
Side: left, right or bilateral
Dominance: dominant or non-dominant side
Position: seated, standing, supine, prone, side-lying or sport-specific position
Device used: force plate, load cell, dynamometer, Muscle Meter or other device
Contraction type: usually isometric unless otherwise defined
Instruction: “fast and hard”, “as quickly as possible”, or other exact cue
Trial number: trial 1, trial 2, trial 3
Final score method: best score, average score or selected trial
Body mass: if normalising RFD
Pain score: before, during or after testing
Symptoms: pain, apprehension, fatigue, cramping or none
Effort quality: explosive, hesitant, submaximal or unclear
Related metrics: peak force, impulse, time to peak, fatigue index, torque or functional test
Baseline comparison: previous result
Retest date: planned follow-up
Progress note: contextual factors that may explain the result
Measurz should be used to support measurement, comparison, monitoring, education and progress tracking. RFD should not be positioned as diagnosing a condition or confirming readiness on its own.
A client has strong peak force but low early RFD.
This may suggest they can produce high force eventually, but not quickly. This may matter for sprinting, jumping, landing or rapid stepping.
A client’s peak force remains similar, but RFD improves after a training block.
This may suggest they are accessing their existing force capacity more quickly.
A client shows low RFD during a push test and reports apprehension.
This may reflect pain, guarding or confidence, not just reduced strength.
An older adult shows low lower-limb RFD and also demonstrates slow stepping responses.
This may provide useful context for balance and function, but should be interpreted with gait, strength and functional testing.
A field sport athlete has good peak force but lower RFD on one side.
This may suggest a rapid force production difference that could be relevant to sprinting or change-of-direction tasks, depending on broader findings.
A client restores peak force symmetry but still shows lower RFD on the previously affected side.
This may indicate that maximal force has improved, but rapid force production remains different.
Rate of Force Development measures how quickly force is produced. It shows the speed of force production during a contraction or movement.
RFD is commonly measured in N/s. It may also be reported in kg/s, kgf/s, lb/s, lbf/s or body-mass-normalised units.
No. Peak force measures how much force is produced. RFD measures how quickly force is produced.
High RFD usually means the client produced force quickly in the tested task. This may be useful when the task requires rapid force production.
Low RFD usually means force was produced more slowly. It may reflect reduced explosive strength, pain, hesitation, fatigue, poor familiarisation or testing differences.
No. RFD is highly dependent on test, device, time window, sampling rate, filtering, start threshold and protocol. Use baseline, side-to-side comparison and matched reference data instead.
It can be, but it is usually more advanced than peak force. RFD is most useful when the client’s goals involve speed, agility, power, balance recovery or dynamic movement.
It may be useful because rapid force production can be relevant to balance and functional tasks, but it should be interpreted with gait, strength, confidence and functional measures.
No. RFD can support assessment and monitoring, but it does not diagnose a condition or explain symptoms by itself.
No. RFD should be interpreted with peak force, impulse, time to peak, symptoms, movement quality, baseline, function and client goals.
RFD measures how quickly force is produced.
It is useful for understanding rapid force production and explosive strength.
High RFD generally suggests faster force production.
Low RFD generally suggests slower force production, but context matters.
RFD is especially relevant when tasks require force to be produced quickly.
There are no universal RFD norms.
RFD is highly sensitive to device, time window, start threshold, filtering and instructions.
Measurz should record RFD with the exact protocol, unit, time window, symptoms and related metrics.
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. https://doi.org/10.3390/sports8050063
Maffiuletti, N. A., Aagaard, P., Blazevich, A. J., Folland, J., Tillin, N., & Duchateau, J. (2016). Rate of force development: Physiological and methodological considerations. European Journal of Applied Physiology, 116(6), 1091–1116. https://doi.org/10.1007/s00421-016-3346-6
Moir, G. L., Getz, A., Davis, S. E., Marques, M., & Witmer, C. A. (2019). The inter-session reliability of isometric force-time variables and the effects of filtering and starting force. Journal of Human Kinetics, 67, 139–151. https://doi.org/10.2478/hukin-2018-0049
Sato, S., Yoshida, N., Akagi, R., Numaguchi, S., & Takahashi, H. (2025). Association of lower-limb strength with different fall histories or physical performance in community-dwelling older adults. BMC Geriatrics, 25, Article 137. https://doi.org/10.1186/s12877-025-05685-3
