What is Reactive Strength Performance?

Ability to change quickly from eccentric to concentric is one quality that can distinguish between the better and the best athletes. This is called as reactive strength. Because eccentric is basically "lengthening" action and concentric is "shortening," reactive strength, therefore, represents the ability to utilize stretch-shortening cycle, or plyometrics.

Dietmar Schmidtbleicher once told me that definition of strength qualities are not invariably consistent, despite "a consensus has been reached" during several conference meetings with his American and European colleagues such as William Kraemer, Steven Fleck, and Keijo Hakkinen. Despite the different terms being used to describe muscle actions, they are intended for the same matter, and fundamentally similar when it comes to actual "practical".

The reactive strength performance considers two components;

1. Time (duration)
2. Displacement (effort)

It is crucial to ask how much forces one can produce in a restricted time, in which movements are likely to occur. For examples, top sprinters' contact time is ~0.08s during the maximal speed, and the take-off in long jump event is ~0.15s. The force that one can generate within these periods will determine the outcome of ensuing action, such as reactivity and displacement. This is the reason for the stride frequency and stride length being the most important determinants of maximal sprint performance. Also, it clarifies the appropriate long jump take-off for being a vital component to attain the long jump distance (displacement) as a result of the generated take-off forces and velocity (from the run-up velocity).

A higher force generation during a contact phase may increase the ground contact time. As a penultimate (last) contact can create a larger "braking action," such as the long jump take-off (~0.15s), it can as well promote a larger impulse and therefore a higher forward force propulsion to launch the body forward.

However, it may not a constituent for other sports contexts as having longer contact phase means the occurrence of excessive (not optimal; too long) braking action also takes place apart from a reduction in the velocity. Hence, an optimal and fast (~0.08s in maximal-sprint; ~0.15s long jump take-off) contact time with a higher force generation can promote a better performance. Again, this is a reactive strength quality (and also explosive strength).

Reactive strength is different from explosive strength

It can be confusing if one wishes to distinguish between the two as both have similar characteristics, and even occurs almost concurrently. Take a look at different definitions and examples.

Definition 1

• Reactive strength - ability to produce a high amount of force in a minimal time.
• Explosive strength - ability to produce a high amount of force in a minimal time.

Definition 2

• Reactive strength - ability to effectively utilize the stretch-shortening cycle in a minimal time upon impact on the ground.
• Explosive strength - ability to generate a higher rise in force production in a minimal time, once a movement has started.

Example 1 - different exercise

• Reactive strength - multiple hurdle jump 
• Explosive strength - box jump (onto a box)

Example 2 - same exercise 

• Reactive strength - landing phase of the drop countermovement jump 
• Explosive strength - extension phase of the drop countermovement jump

Example 3 - long jump

• Reactive strength - the take-off action, a fast stretch shortening cycle 
• Explosive strength - the rapid flexions and extensions of muscles involved

Regardless of definitions, both strength qualities are crucial and they can be the major part (performance determinants) of any high-speed, repetitive, and powerful movements such as sprinting, change of direction, and quickness.

Reactive strength is also linked to Rate of Force Development (RFD), which has been explained earlier.