Rate of force development (RFD)

Rate of force development (RFD) is the change in force divided by the change in time.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 539.} Producing maximal force takes at least 300 milliseconds, while many sport actions last 0 to 200 milliseconds; faster acceleration requires applying force at a greater rate.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 539.}

Zatsiorsky puts the cutoff at about 0.3 seconds: when a movement allows less time to produce force, RFD rather than maximal strength decides the outcome.^{2Zatsiorsky, Kraemer and Fry, Science and Practice of Strength Training, 3rd ed., p. 236.}

In practice

• Heavy squatting (70 to 120% of 1RM) raises maximal isometric strength but hasn’t been shown to improve RFD and may reduce it.^{3Hoffman, NSCA’s Guide to Program Design, p. 122.} Light jump squats with maximal effort do improve it.^{3Hoffman, NSCA’s Guide to Program Design, p. 122.}
• Strength still matters for beginners: in clients without a strength base, maximal lifting can raise RFD, though it may do little for highly trained clients.^{2Zatsiorsky, Kraemer and Fry, Science and Practice of Strength Training, 3rd ed., p. 236.}
• To train RFD directly, use bursts of muscle action against high loads, performed as fast as possible with maximal effort.^{2Zatsiorsky, Kraemer and Fry, Science and Practice of Strength Training, 3rd ed., p. 236.} Do them rested, usually right after the warm-up.^{2Zatsiorsky, Kraemer and Fry, Science and Practice of Strength Training, 3rd ed., p. 236.}
• Combine resistance, plyometric and sprint training for the biggest gains.^{4International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 353.}