What is Reactive Strength Performance?

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

Broadly, reactive strength performance considers two components;

1. Time (duration)
2. Force (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 total force one can generate within these short periods can determine the outcome of ensuing actions, including reactivity performance and forward (or upward) displacement.

It also clarifies why the  take-off phase during the long jump is vital for attaining the long jump distance (displacement) due to the time to be spent for generation of a large sum of take-off forces (combined with speed from the run-up).

Logically, a high force generation during a contact phase is concomitant with increased ground contact time, and vice versa. This can be good, or bad, its depend... For example, in long jump, the penultimate (take-off) contact leads to braking action, but in turn, creates a larger impulse that promotes higher forward force propulsion that assist the launch the body forward.

This force generation ability will contribute to maximal sprinting performance as well, but not to the extent of the take-off phase during long jump that appears to be counterproductive for sprinting due to braking action. Braking action as low as 0.02 seconds (e.g. 0.10s to 0.12s during each ground contact, 20%) will largely affect sprinting performance, by reducing sprinting velocity.

Hence, optimal contact time during a specific context (~0.08s for maximal-velocity phase, or ~0.15s long jump take-off) is the key. Keep in mind that a higher force generation combined with optimal contacts can promote a better performance. In short, these context-specific actions are related to reactive strength and explosive strength qualities.

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 (point 1: similar)

• 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 (point 2: the difference between reactive- vs explosive-strength)

• 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

• 

  Drop jump exercise (reactive strength)

  Reactive strength - multiple hurdle jumps 
• 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 - during 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.