Rate of force developmentRFD

Rate of force development is how quickly you can produce force, measured as the slope of the force-time curve rather than its peak. Maximal strength asks how much force you can eventually generate; RFD asks how much you can generate in the first hundred or two hundred milliseconds.

That window matters because many real tasks do not allow more time. A sprint step, a jump, a change of direction and catching yourself as you trip all resolve faster than peak force can be reached, so the early part of the curve is what actually gets used.

It depends heavily on the nervous system: how quickly motor units are recruited, how fast they fire initially, and how well the movement is coordinated. It also depends on tendon stiffness, since a compliant tendon takes up slack before force reaches the bone.

It is trained by intent rather than by load alone. Moving a moderate weight as fast as you can, jumps, throws and short sprints all develop it, and doing that work fresh matters, because the same exercises performed fatigued become slow work training something else.

It declines with age faster than maximal strength does, which is a specific and underappreciated risk. Recovering from a stumble is an RFD task, so a person can be strong enough to stand from a chair and still too slow to catch a fall.

That makes fast, safe, supervised work a legitimate part of training in later decades rather than something reserved for athletes.

In practice, put a small amount of explosive work at the start of sessions, track it over years with something simple like our vertical jump calculator, and treat speed as a quality to maintain rather than one to retire from.