Rate of Force Development: How It’s Measured and Improved

Maximal strength tells you how much force a muscle or movement can eventually produce. But many movements do not provide enough time to reach maximal force.

A sprint start, jump, change of direction, or attempt to stabilize a joint after an unexpected movement can occur within fractions of a second. In these situations, the speed at which force becomes available can matter as much as the total amount of force that can be produced.

Rate of force development (RFD) describes how quickly force rises after a muscle contraction begins. It is commonly used to assess explosive strength and neuromuscular function through the relationship between force and time.¹

The rate of force development can reveal what traditional maximal-strength tests may miss. The sections below cover how RFD is calculated, what influences it, why early and late RFD represent different qualities, and how training can change force production over short time periods.

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What is the rate of force development?

Rate of force development is the change in force divided by the change in time at the beginning of a muscle contraction.¹

In simple terms:

Rate of force development = change in force ÷ change in time

RFD is often expressed in newtons per second (N/s) when force is measured directly or newton-meters per second (Nm/s) when joint torque is measured.

Imagine two people who can each eventually generate 1,000 N of force:

●      Person A reaches 500 N after 100 milliseconds.

●      Person B reaches only 300 N after 100 milliseconds.

Their maximal force may eventually be identical, but Person A develops usable force sooner. That distinction is what RFD is intended to capture.

Many movements provide only a limited window for force production. Research on RFD commonly examines periods such as the first 50, 100, 150, or 200 milliseconds after contraction begins.¹

RFD is usually described as the slope of a force-time curve. A steeper rise means force is being generated more quickly.

Early versus late rate of force development

Researchers often divide RFD into early and later portions of the contraction.

Early RFD, frequently examined within approximately the first 50 to 100 milliseconds, appears to depend heavily on neural factors, particularly how quickly the nervous system recruits and activates motor units.¹

Later RFD, measured farther into the contraction, is increasingly influenced by maximal strength and the force-producing capacity of the muscle.¹

That difference helps explain how two people with similar maximal strength can show very different force-time profiles.

A person may have sufficient muscle capacity to produce considerable force but lack the ability to activate it quickly. Another may display strong early neural activation while having a lower maximal force ceiling.

For this reason, maximal strength and rate of force development should not automatically be treated as interchangeable measurements.

Why does the rate of force development matter?

Many physical tasks occur too quickly for maximal force to be reached.

During sprinting, jumping, cutting, landing, and other short-duration movements, the body may have only a few hundred milliseconds or less to generate force.

Research has found associations between RFD and several measures of physical performance. For example, one study examining countermovement jumps found that peak RFD was significantly associated with vertical jump displacement.² Other findings have been less clear-cut. A larger analysis of countermovement jumps in more than 2,000 collegiate athletes found that peak RFD predicted jump height on its own, but accounted for little additional variance once other variables were included in the model.³

That does not mean RFD alone determines performance. Technique, coordination, maximal strength, power, tendon properties, movement velocity, and other factors all contribute.

RFD instead gives another view of how strength is expressed under time pressure.

Rate of force development and joint control

The same concept can matter during rehabilitation.

Joint stabilization often requires force to be produced before maximal strength has time to develop. Following an unexpected perturbation or fast change in load, muscles may have only a short window in which to respond.

A review focused on sports injury rehabilitation noted that deficits in RFD may remain even after maximal strength has returned.⁴ This suggests that restoring a maximal-strength value does not necessarily indicate that force can be produced at the same speed as before injury.

Research following ACL reconstruction has also examined relationships between RFD, jump performance, and knee mechanics, illustrating growing interest in force-time characteristics during return-to-activity testing.⁵

This is one reason rehabilitation may include both traditional strength development and tasks that progressively challenge the speed of force production.

Medbridge provides additional resources for physical therapy and therapeutic exercise programming that can support progressive rehabilitation across different stages of recovery.

What determines the rate of force development?

RFD is influenced by a combination of nervous-system, muscular, and mechanical factors.

Their relative influence varies with how much time has passed since contraction began.

Neural drive

During the earliest portion of a contraction, the nervous system plays a major role in how quickly force rises.

Motor units must be recruited and begin firing at sufficiently high rates to create force. Research suggests that the ability to generate high voluntary activation during approximately the first 50 to 75 milliseconds is a major contributor to early RFD.¹

Higher initial motor-unit discharge rates allow force to rise sooner after the onset of contraction.

This helps explain why training intended to generate force quickly can influence RFD, even when external movement is limited.

Maximal strength

Maximal strength becomes increasingly relevant as more time becomes available for force production.

Someone with a larger strength reserve has a higher potential force ceiling. Once the contraction extends beyond its earliest phase, this additional capacity can contribute more strongly to the force-time curve.¹

As a result, heavy strength training can contribute to RFD improvements even when the exercises themselves are not performed at extremely high movement velocities.

Muscle and tendon characteristics

Muscle architecture, muscle fiber characteristics, tendon stiffness, contraction properties, and excitation-contraction processes can also influence how force is transmitted and developed.⁶

Disuse illustrates why these characteristics matter.

A recent review of muscle unloading found that explosive strength can decline more than maximal strength during periods of disuse. Proposed mechanisms include reductions in motor-unit firing rates, altered recruitment thresholds, changes in muscle contraction characteristics, and decreased tendon stiffness.⁶

The ability to produce force quickly, therefore, represents a different dimension of neuromuscular function than maximal strength alone.

How is the rate of force development measured?

RFD is typically calculated from force or torque data collected during a contraction.

Testing may use equipment such as:

●      Force plates

●      Isokinetic dynamometers

●      Load cells

●      Instrumented strength-testing systems

A person might perform an isometric knee extension or isometric mid-thigh pull while being instructed to produce force as hard and as quickly as possible.

Researchers then identify the beginning of the contraction and calculate the slope of the force-time curve across selected intervals.

Common measurements include:

RFD 0–50 ms: Force development during the first 50 milliseconds.

RFD 0–100 ms: Force development during the first 100 milliseconds.

RFD 0–200 ms: Force development during the first 200 milliseconds.

Peak RFD: The highest measured slope of the force-time curve.

Using multiple time intervals can provide more information than relying on a single RFD value, as the physiological contributors to force production change throughout the contraction.¹

Measurement reliability matters

RFD can be more difficult to measure consistently than maximal strength.

The earliest portions of the force-time curve can be particularly variable. Within-subject reliability has been reported to be low during the first approximately 50 milliseconds and good from about 100 milliseconds onward. That variability may make the earliest measurements better suited to detecting group-level change than individual-level change.¹^,⁷

Testing procedures need to be standardized when comparing RFD values over time. Positioning, instructions, warm-up, equipment, contraction-onset criteria, sampling frequency, and analysis methods can all influence the results.

This also means that small changes in RFD should be interpreted with caution. A higher number on a second test does not automatically mean neuromuscular capacity has meaningfully changed.

How can the rate of force development be improved?

Both heavy resistance training and training performed with an emphasis on producing force quickly can improve RFD.¹

A systematic review and meta-analysis of 54 studies found that resistance training increased both early and later RFD. Training that used faster movement speeds, intent to produce force quickly, and movement patterns similar to the test tended to produce larger improvements in peak RFD.⁸

This does not mean every repetition needs to occur at high external velocity.

A heavy squat, for example, may move slowly because of the load. The person can still attempt to apply force as quickly as possible against the resistance.

Training options used to target RFD may include:

●      Heavy resistance exercises performed with maximal acceleration intent

●      Jumping and landing progressions

●      Ballistic exercises

●      Olympic-lifting derivatives

●      Isometric contractions with an emphasis on fast force production

●      Sprinting and acceleration drills

●      Resisted sprinting

●      Task-specific movements performed under appropriate loading

Exercise selection depends on the goal, current physical capacity, training history, injury status, and movement being developed.

Medbridge's exercise programming resources can support progressive exercise prescription as force production is rebuilt during rehabilitation.

A practical rate of force development example

Consider someone returning to higher-level activity after a knee injury.

An isometric strength test shows that the peak knee-extension force between the involved and uninvolved limbs is nearly equal. Looking only at maximal strength could suggest that force capacity has largely returned.

Force-time testing tells a different story.

At 200 milliseconds, the limbs are similar. At 100 milliseconds, however, the involved limb produces considerably less force.

This indicates that maximal strength has recovered more fully than the ability to express that strength quickly.

Programming could then continue to build maximal strength while gradually adding exercises that emphasize faster force production, such as controlled ballistic tasks, jumps, acceleration work, or fast-intent resistance exercise as appropriate.

Follow-up testing could examine both peak force and selected RFD intervals, rather than relying on a single measurement.

The rate of force development adds a time component to strength assessment. It asks a different question from maximal strength: How much force can be produced in the time actually available?

That makes RFD useful for studying explosive movement, neuromuscular function, fatigue, physical performance, and recovery from injury. Used alongside maximal strength and movement-specific measures, the force-time curve can show more about how force is produced and how that capacity changes with training or rehabilitation.

Rate of force development offers another way to understand how strength translates into movement when time is limited. Building the ability to produce force sooner requires thoughtful assessment, progressive loading, and training that connects strength with speed and movement demands. Medbridge offers Strength and Conditioning Continuing Education through evidence-based courses, exercise resources, and training content to support ongoing professional development and performance programming.

References

1. Maffiuletti NA, Aagaard P, Blazevich AJ, et al. Rate of force development: physiological and methodological considerations. European Journal of Applied Physiology. 2016;116(6):1091–1116.
   Full text on PMC

2. McLellan CP, Lovell DI, Gass GC. The role of rate of force development on vertical jump performance. Journal of Strength and Conditioning Research. 2011;25(2):379–385.
   PubMed

3. Miller JD, Fry AC, Ciccone AB, Poggio J. Analysis of rate of force development as a vertical jump height predictor. Research Quarterly for Exercise and Sport. 2023;94(3):638–645.
   PubMed

4. Buckthorpe M, Roi GS. The time has come to incorporate a greater focus on rate of force development training in the sports injury rehabilitation process. Muscles, Ligaments and Tendons Journal. 2018;7(3):435–441.
   Full text on PMC

5. Graham MC, Reeves KA, Janatova T, Noehren B. The relationship of open- and closed-kinetic-chain rate of force development with jump performance following anterior cruciate ligament reconstruction. International Journal of Sports Physiology and Performance. 2024;19(6):585–592.
   PubMed

6. Ruggiero L, Gruber M. Neuromuscular mechanisms for the fast decline in rate of force development with muscle disuse: a narrative review. The Journal of Physiology. 2026;604(2):735–760.
   PubMed

7. Blazevich AJ, Wilson CJ, Alcaraz PE, Rubio-Arias JA. Effects of resistance training movement pattern and velocity on isometric muscular rate of force development: a systematic review with meta-analysis and meta-regression. Sports Medicine. 2020;50(5):943–963.
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