What is reactive strength?

Reactive strength is your ability to switch quickly from absorbing force to producing it. It is often measured with the reactive strength index from a drop jump, comparing jump height against ground contact time, and it underpins sprinting, cutting, and repeated jumping.

Why it is a separate quality

Maximal strength describes how much force you can produce with unlimited time. Reactive strength describes how well you use force in the fraction of a second available during a sprint step or a change of direction. Strong athletes can score poorly here, which is why heavy lifting alone does not automatically make someone fast or springy.

How it is measured

The reactive strength index divides jump height by ground contact time in a drop jump. A high figure means you jumped well without spending long on the ground. It can be assessed with a jump mat or a contact timer, and even a phone camera at high frame rate gives a usable comparison over time.

What determines it

• Tendon stiffness: Stiffer tendons return stored energy more effectively.
• Eccentric strength: You have to absorb the landing before you can redirect it.
• Neural timing: Muscles must pre-activate before ground contact so the limb is stiff on arrival.
• Technique: Where the foot lands relative to the body changes everything.

How to train it

Begin with pogo hops and ankle hops, cueing minimal ground contact and stiff ankles. Progress to lateral bounds to a stick landing and bounding, then to depth jumps from modest heights. Keep volume low and quality high; this quality disappears with fatigue faster than any other.

The strength prerequisite

Reactive work involves absorbing large forces, so a base of eccentric and maximal strength should come first. Introducing depth jumps to an athlete who cannot control a single-leg landing is the classic route to knee and Achilles complaints.

Where it shows up

Sprinting, changing direction, repeated jumping in court sports, and running economy all draw on it. See Reactive Strength and Elastic Qualities for a full treatment.