What is Rate of Force Development?

What is Rate of Force Development?

Rate of force development is how fast you can turn on muscular force, not how much force you can eventually produce. Picture pushing as hard and as fast as possible against an immovable bar or force plate from a dead stop: the resulting force-time curve starts at zero and climbs toward your true maximum voluntary contraction.

RFD is the steepness of that climb, usually reported as the average slope over a fixed early window, such as 0 to 50, 0 to 100, or 0 to 200 milliseconds from the first sign of force, rather than the eventual peak. This distinction matters because two lifters can share an identical one-rep max back squat and still separate by 30 to 40 percent in vertical jump height or sprint acceleration, since the squat 1RM only tests how much force you can generate given unlimited time, while jumping, sprinting, changing direction, and throwing all happen inside a window of roughly 80 to 250 milliseconds, far shorter than the 300 to 400 milliseconds an untrained nervous system typically needs to reach true peak force.

Coaches and sports scientists track RFD because it is the quality actually expressed on the field, court, or track, where there is rarely enough time to reach maximal strength before the movement is already over. High RFD is what lets a sprinter's foot generate enough push during a 90-millisecond ground contact, or a volleyball player produce enough vertical force before a countermovement jump is already airborne.

How it works

Rate of force development comes from a two-phase handoff between the nervous system and the muscle itself, visible when you split a force-time curve into an early and a late window. In the first 50 to 75 milliseconds after contraction onset, force rise is driven almost entirely by neural drive: how many motor units the nervous system recruits and how fast those motor units fire.

Trained, explosive muscle can produce initial motor unit discharge rates above 200 Hz, including doublet discharges of two spikes fired within a few milliseconds, compared with roughly 60 to 120 Hz in untrained muscle, and this rate coding, not muscle size, explains most of the variance in early RFD. Past about 75 to 100 milliseconds, the muscle's own contractile and structural properties take over as the limiting factor: fiber type composition (type II fibers cycle cross-bridges faster than type I), physiological cross-sectional area, and musculotendinous stiffness increasingly set the ceiling.

Maximum voluntary contraction strength itself explains only around 18 percent of the variance in force at 10 milliseconds but climbs to explain roughly 57 to 78 percent of the variance by 100 to 200 milliseconds, which is why heavy strength training raises late-phase RFD even though it barely touches the earliest neural window. Force plates and isometric dynamometers capture this by sampling force at 1,000 Hz or faster during a maximal isometric mid-thigh pull or knee extension, marking contraction onset at a small fixed threshold above baseline noise, then calculating the slope between onset and each subsequent time point on the curve.

The formula

RFD = ΔForce ÷ ΔTime (reported in N/s)

Practical read: RFD0-50ms reflects almost pure neural drive; RFD100-200ms increasingly reflects muscle size, fiber type, and tendon stiffness. Peak RFD is the single steepest 1- to 20-millisecond slope anywhere on the curve, usually reached 40 to 90 milliseconds after contraction onset.

How to apply it

• Heavy resistance training: Lifting at 85 percent of 1RM or higher with maximal intended bar speed raises late-phase RFD (past roughly 100 ms) by increasing muscle cross-sectional area and neural drive, matching the outcome of Aagaard's 14-week heavy-training study.
• Dynamic effort / ballistic training: Loads of 30 to 55 percent of 1RM moved as fast as possible, such as jump squats, medicine ball throws, or bar-speed-tracked bench presses, target early-phase RFD by training maximal motor unit firing rate.
• Plyometrics: Depth jumps, box jumps, and bounding use a fast stretch-shortening cycle with ground contacts under 250 milliseconds, training the muscle-tendon unit to store and release elastic energy quickly.
• Olympic-lift derivatives: Power cleans, hang pulls, and jump shrugs combine a heavy load with triple extension performed explosively, overlapping the benefits of strength training and ballistic training in one movement.
• Contrast training: Pairing a heavy set of 3 to 5 reps near 85 percent 1RM with a biomechanically similar explosive movement 1 to 4 minutes later, such as a back squat into a jump squat, uses post-activation performance enhancement to raise force output in the following set.
• Maximal-intent isometrics: Pushing as hard and fast as possible against an immovable bar, as in an isometric mid-thigh pull, trains the nervous system to reach high motor unit firing rates without the technical demands of a moving load.

Types

Worked example

Here is a simplified isometric mid-thigh pull force-time trace for a trained field-sport athlete, split into the standard reporting windows. Notice how the interval RFD climbs through each window while the athlete is still far from peak force, and compare that to how briefly a sprint or jump actually lasts.

A sprinter's foot is only on the ground for about 80 to 120 milliseconds, and a countermovement jump takes off around 200 to 300 milliseconds after the athlete starts pushing — both events are over before this athlete even reaches peak force at roughly 320 milliseconds. Whatever force got produced inside that early window is the force that actually moved the athlete; the last 1,000-plus newtons of peak strength never got used.

Rate of force development vs maximal strength (1RM)

The two qualities correlate, since stronger athletes generally show higher late-phase RFD, but the relationship is loose enough that athletes with matched 1RMs can differ by 30 to 40 percent in jump height or sprint acceleration. Train both: strength training raises the force ceiling, and ballistic training teaches you to reach a higher fraction of it, faster.

By goal

• Team-sport, sprint, and jump athletes: Prioritize ballistic training, plyometrics, and Olympic-lift derivatives at 30 to 55 percent 1RM, paired with 1 to 2 heavy strength sessions a week so the force ceiling keeps rising alongside speed of expression.
• Powerlifters and strength/power athletes: Heavy training already builds late-phase RFD; add compensatory acceleration work, moving submaximal loads of 50 to 70 percent 1RM as fast as possible on the concentric, plus jump squats, to sharpen early-phase neural drive without sacrificing the strength base.
• Older adults and rehab populations: Because RFD declines faster with age than maximal strength does, train explosive intent at light-to-moderate loads, such as fast chair-rise drills or light band presses moved quickly, alongside general resistance training to protect fall-recovery capacity and daily function.

Common misconceptions

• "Rate of force development is basically the same thing as strength." They are related but distinct qualities. Two lifters can post an identical 1RM back squat and still differ by 30 to 40 percent in vertical jump or sprint acceleration, because 1RM tests unlimited-time force while RFD tests force produced in the first 50 to 200 milliseconds.
• "Only light, fast, ballistic training improves rate of force development." Aagaard's 2002 training study found 14 weeks of heavy resistance training near 1RM raised RFD as much as explosive training did, mainly by increasing neural drive and late-phase force capacity. Heavy and ballistic training improve RFD through different, complementary mechanisms.
• "Rate of force development only matters for elite sprinters and jumpers." RFD governs any movement faster than about 300 milliseconds, including a recreational lifter's bar speed off the chest on bench press, a basketball player's first step, and an older adult's ability to catch themselves during a stumble before a fall.
• "A higher 1RM always means you will jump higher or sprint faster." Ground contact in sprinting lasts roughly 80 to 120 milliseconds and a jump takes off around 200 to 300 milliseconds, both well short of the 300 to 400 milliseconds most lifters need to reach peak force, so RFD inside that window predicts performance better than peak strength alone.

Related terms

Rate of Force Development FAQ

What is rate of force development in simple terms?

Rate of force development is how quickly your muscles can build up force from a resting state, rather than how much force you can eventually produce. It is calculated as the change in force divided by the change in time and is usually measured in newtons per second on a force plate.

How is rate of force development measured?

RFD is measured with a force plate or dynamometer during a maximal effort, most often an isometric mid-thigh pull or isometric knee extension. Software marks the onset of force and calculates the slope of the force-time curve over fixed windows such as 0 to 50, 0 to 100, and 0 to 200 milliseconds.

What is a good rate of force development?

There is no single universal benchmark, because RFD scales with body mass, training status, and the exact test used. Trained field-sport athletes commonly post RFD0-200 values several times higher than untrained adults on the same isometric mid-thigh pull test, so track your own trend rather than chasing a published number.

Is rate of force development the same as power?

They are closely related but not identical. Power is force multiplied by velocity at any instant, while RFD is specifically how fast force rises from zero. High RFD usually produces high power output, which is why both qualities get trained together with jumps, throws, and Olympic-lift derivatives.

How can I improve my rate of force development?

Combine heavy resistance training near 85 percent of your 1RM with ballistic work like jump squats and medicine ball throws at 30 to 55 percent of 1RM moved as fast as possible. Plyometrics, Olympic-lift derivatives, and contrast training also raise RFD by targeting different phases of the force-time curve.

Does heavy lifting improve rate of force development?

Yes. A 14-week heavy resistance training study by Aagaard and colleagues found meaningful increases in RFD and neural drive after training with loads near 1RM, even without any explosive or ballistic exercises in the program. Heavy training mainly raises the later, muscle-dependent part of the force-time curve.

Why do two lifters with the same squat max jump differently?

Because a one-rep max tests force production with no time limit, while jumping happens inside a 200 to 300 millisecond window. The lifter with higher rate of force development reaches more of their available strength within that window and therefore applies more force against the ground before takeoff.

Does rate of force development decline with age?

Yes, and typically faster than maximal strength does. Research comparing young and older adults found rapid force characteristics dropped by roughly 39 to 64 percent with age compared with 29 to 46 percent for maximal isometric strength, which is why RFD training is relevant for fall prevention in older adults.

What is the difference between RFD and explosive strength deficit?

Explosive strength deficit compares the force you produce during an explosive attempt at a fixed early time point against your true maximum voluntary force; a large gap signals untapped strength you are not yet expressing quickly. RFD itself is the raw speed of force rise that produces that early time-point force.

What sports rely most on rate of force development?

Sprinting, jumping, throwing, change-of-direction sports, and Olympic weightlifting all depend heavily on RFD because their key actions happen in well under 300 milliseconds. Even sports built around maximal strength, like powerlifting, benefit from RFD for bar speed off the chest or floor during competition attempts.

References

1. Maffiuletti NA, Aagaard P, Blazevich AJ, Folland J, Tillin N, Duchateau J. Rate of force development: physiological and methodological considerations. European Journal of Applied Physiology, 2016
2. Aagaard P, Simonsen EB, Andersen JL, Magnusson P, Dyhre-Poulsen P. Increased rate of force development and neural drive of human skeletal muscle following resistance training. Journal of Applied Physiology, 2002. PMID 12235031
3. Cormie P, McGuigan MR, Newton RU. Developing maximal neuromuscular power: part 1 — biological basis of maximal power production. Sports Medicine, 2011. PMID 21142282
4. Cormie P, McGuigan MR, Newton RU. Developing maximal neuromuscular power: part 2 — training considerations for improving maximal power production. Sports Medicine, 2011. PMID 21244105
5. D'Emanuele S, Maffiuletti NA, Tarperi C, Rainoldi A, Schena F, Boccia G. Rate of Force Development as an Indicator of Neuromuscular Fatigue: A Scoping Review. Frontiers in Human Neuroscience, 2021
6. Thompson BJ, Ryan ED, Herda TJ, Costa PB, Herda AA, Cramer JT. Age-related changes in the rate of muscle activation and rapid force characteristics. Age (Dordrecht), 2014;36(2):839-849
7. The Role of Rate of Force Development in Bench Press Performance. NSCA Coach, National Strength and Conditioning Association