Reactive strength is the ability to rapidly change from an eccentric contraction to a concentric contraction. It is the athletes ability to absorb forces in a minimal time and to very quickly use those forces to generate maximal force in another direction that makes the athlete "pop". It is not a new term but its true meaning is often misunderstood including the mechanisms behind it and how to properly train for its emergence.
Establishing POint B: Reactive Strength
In simple terms, reactive strength is related to athleticism. Athletes often stand out from one another in their unique ability to seamlessly change direction, accelerate or get off the ground quickly.
Often the concept of athleticism is aligned with the agility and the mechanisms of how this occurs is traditionally thought of as the stretch shortening cycle of plyometrics and tendon stiffness.
Here in lies one of the training misconceptions regarding reactive strength.
Inherent in reactive strength lies the element of explosive strength. Explosiveness in strength training terms is rate of force development. Some misconstrue athleticism with purely explosive strength, which only provides part of the puzzle.
This leads to a second misconception.
It is therefore more appropriate to think of explosive strength as a special strength quality that is the summation of both reactive strength and rate of force development.
Explosive output is a result of reactive strength which is a tissue specific output and rate of force production which is a CNS output.
It is evident that explosiveness or athleticism is a combination of specific tissue capacity as well as the capacity of the CNS.
This detail is often overlooked in our understanding of reactive strength and its role in explosiveness which leads to improper training of this tissue specific quality.
Perceived Mechanisms of Reactive Stregth
There are two main mechanisms in the literature associated with reactive strength. One is the stretch shortening cycle (SSC) and the other is tendon stiffness.
The basics of the SSC is actually the definition of reactive strength, loading eccentrically then quickly unloading concentrically during the performance of a movement.
The action of the SSC might be best analogized as a spring-like mechanism. Compressing the coil causes it to rebound off a surface or in a different direction. Increasing the speed of the coil or how hard it is compressed will result in the spring jumping higher and farther. This increases the rate of loading. Again, this analogy brings together the rate of force production and reactive strength.
One of the most interesting and important aspects of the SSC is the Amortization phase. This is the time between the loading and unloading phases and is a huge key to understanding reactive strength and its impact on performance.
To analogize further, a mortgage has an amortization phase, where the buyer wants to reduce the amortization phase and payoff the house.
In high performance as with a loan, the shorter the amortization phase the better!
Athletic movements that have shorter ground contact times and a decreased amortization rate, would have a faster SSC...like running.
Movements like walking, that occur slower and have a greater ground contact time and have a slower SSC.
Tendon stiffness is widely discussed as having great impact on reactive strength. This is based on reflexive activities of each receptor that is hypothesized to increase motor unit recruitment and therefore increases muscular output. This output is then "sent" through a stiff tendon to create an explosive movement and is therefore a component of reactive strength.
A progressive view
The literature surrounding reactive strength, understanding its mechanism, and training come from a misunderstanding of soft tissues and how they interact and the role of the CNS.
Traditional thinking totally negates the impact of connective tissue, both inter and intra-muscular muscularity and how the behavior and architecture of the tissue at all muscle levels has a profound impact on reactive strength.
Reactive strength is a tissue specific capacity that must be adequately trained to maximize the neurological manifestation of it.
A breif word about inter and intra muscualr connective tissue
Connective tissue exists and is continuous throughout a muscle at all levels. This is an important detail as it suggests that due to the continuous nature of connective tissue it will behave the same (or similarly) at all levels under load and its behavior will determine reactive strength.
Reactive strength is a representation of fast SSC function. The amortization phase between a rapid change must be short. This requires that the potential energy stored during the eccentric contraction must then be quickly used kinetically to generate a quick and forceful movement.
What tissue is best suited for this?
Behaviorally, connective tissue is designed specifically for this purpose. Connective tissue has been repeatedly shown that it is a specific energy-absorbing and dissipating tissue.
The role of the cns
Due to the output of reactive strength bearing on fast SSC function, the role of the CNS may be understated.
The neurophysiological mechanisms occur too slowly to be the predominant mechanism of reactive strength as explosive movement in sport happens much quicker.
This doesn't mean that the CNS does not have an effect on reactive strength, it just does so indirectly.
Recall that reactive strength is a part of explosive strength. Explosive strength is also a product of rate of force production. RFP is highly dependent on maximal strength capacity which is entirely a neurological mechanism of strength.
The role of the CNS in the emergence of reactive strength, is negligible and has no bearing of the role of the connective tissue. The neurological capacity of absolute strength does have an indirect effect.
Gearing and its effect on reactive strength
The dynamic interaction of muscle and connective tissue is termed structural gearing.
Gearing is a mechanism that allows muscles to partially circumvent force-velocity constraints to fiber performance.
During muscle contraction, fibers can rotate essentially changing their angle, so the pennation angle can increase.
For fast SSC contractions, the connective tissue must stiffen at length so the fascicles can generate a "pull".
This allows for an output of force to be produced.
Gearing occurs at each fascicle by rotating in unison, which allows for a very rapid output that occurs far quicker the CNS can account for.
This forms the mechanism of reactive strength.
Training for reactive strength
Training for reactive strength has a broad base in the strength literature. The obvious means for training for it would be with the use of plyometrics.
Herein lies a training conundrum with respect to reactive strength that is missed in most (if not all) training programs.
Plyometrics have been shown to have minimal effect on tissue specific properties but have great effects on the neurological mechanisms of strength.
Reactive strength is a tissue specific capacity and must be appropriately trained. To maximize the neurological effects of fast SSC based plyometrics.
Biology before neurology! The tissue must be in place and trained for appropriate capacity before interacting with the neurology.
Tissue Specific training for reactive strength
It is important to build the behavior of connective tissue stiffness (energy absorption and dissipation) as a method of building the emergence of reactive strength.
The intent of connective tissue training for reactive strength is to build load bearing capacity . Reactive strength's foundation in essence is to create efficiency of energy absorption.
To do so, the programmer must consider the rate of force absorption, the amount of load to be absorbed and the range of motion this needs to occur.
In addition, because reactive strength the velocity of the training stimulus must be considered. Dynamic efforts are required.
The basic progression to training reactive strength is to begin to prepare the connective tissue at length and impart force to improve energy efficiency.