Rate of Force Development
Rate of Force Development (RFD) refers to the speed at which force increases during a muscular contraction. Mathematically, this is expressed as the change in force divided by the change in time.
- RFD = ΔForce ÷ ΔTime
RFD is a critical factor that determines power and athletic performance, as it indicates how quickly an individual can generate force. This is especially true for high-velocity activities like sprinting, jumping, throwing, cutting, and Olympic lifts. Unlike maximal strength, which refers to the total force that can be generated regardless of the amount of time required, RFD emphasizes how rapidly force increases; for example, research often refers to the first 200 milliseconds of a contraction.
- Related Topics: Power , Plyometric Exercise , Stretch-shortening Cycle , Force-velocity Curve , Amortization Phase , Rate of Force Development , Counter-movement Jump (CMJ)
Related Courses:
- Power (High-velocity) Training: Introduction
- Lower Body Power Exercises
- Upper Body Power Exercises and Total Body Power Exercises
Frequently Asked Questions (FAQ):
What is the rate of force development (RFD)?
- RFD measures how quickly force increases during muscle contraction. It’s calculated by dividing the change in force by the time it takes to produce that force and is typically expressed in Newtons per second (N/s).
Why is RFD important in sports and performance training?
- Most athletic tasks, like jumping, sprinting, and changing directions, occur in less than 250 milliseconds. Because peak force takes longer to develop, athletes rely on a high RFD to apply meaningful force within these short timeframes. Higher RFD = better explosiveness.
How is RFD different from power?
- RFD measures how quickly force is developed, while power measures the rate at which work is done (force × velocity). For example, during a depth jump, the RFD by the muscular system may be measured during the amortization phase (time on the ground) to determine the force required to go from the eccentric phase to the concentric phase. Whereas power would measure the force x the distance jumped, divided by how long the jump took.
How can I improve my rate of force development?
- RFD can be improved through power and plyometric exercises (e.g., jumps, throws, etc.). Additionally, heavy strength training with the intent to overcome the amortization phase and increase concentric velocity may also improve power. Note, strength training is more beneficial when added to power and plyometric exercise. Further, emphasis should be placed on high intent, rapid contractions, and attention should be paid to appropriate progression to avoid overtraining.
Can RFD be measured?
- Yes. RFD is typically measured in laboratory settings using force plates or isokinetic dynamometers, although field-based proxies (e.g., vertical jump tests or sprint acceleration) are often used in applied settings.
Does RFD decline with age?
- Yes. Like power, RFD declines more rapidly than maximal strength due to age-related losses in fast-twitch muscle fibers and neuromuscular responsiveness. This makes RFD training especially important for aging adults to maintain functional ability and prevent falls.