Understanding the Evolution of Force Development Training
The fitness industry often uses terminology inconsistently, creating confusion among practitioners and clients alike. One such area is reactive training—a methodology frequently conflated with plyometrics but encompassing a broader spectrum of training approaches. This article clarifies these concepts and provides a comprehensive framework for implementing reactive training across diverse populations.
Plyometrics vs. Reactive Training: Defining the Difference
Plyometric exercises are traditionally defined as movements featuring a rapid eccentric (pre-stretch) contraction followed immediately by an explosive concentric contraction. This sequence activates what exercise scientists call the stretch-shortening cycle (SSC)—a neuromuscular mechanism that enhances force production through elastic energy return and neurological facilitation.
True plyometrics, originally developed by Soviet scientist Yuri Verkhoshansky in the 1960s, was termed “Shock Method” training. This approach involved intense, high-impact exercises designed specifically for elite athletes. The term “plyometrics” itself was introduced later, in 1975, by American track and field coach Fred Wilt, who interpreted these exercises as movements that “invoke the stretch reflex in muscle” through an “overload of isometric-type muscle action.”
The distinction between reactive training and plyometrics lies in scope:
- Plyometrics (Shock Method): Extremely rapid force coupling (0.15-0.2 seconds between eccentric and concentric phases) with high neural demands
- Jump Training: Less intensive movements that utilize similar mechanisms but with reduced neural stress and eccentric demands
- Reactive Training: An umbrella term encompassing both approaches along a continuum, with graduated intensity and application
Reactive training broadly refers to any exercise that enhances the body’s ability to rapidly absorb force and then immediately produce force—making it more inclusive and adaptable to various populations than strict plyometric protocols.
The Science Behind Reactive Training
The Stretch-Shortening Cycle: Mechanics and Neurology
The stretch-shortening cycle that underpins reactive training consists of three distinct phases:
Phase I: Eccentric Loading (Pre-Stretch)
- The agonist muscle groups lengthen under tension
- Elastic energy is stored in the series elastic component (SEC)
- Muscle spindles detect the rapid stretch and initiate the stretch reflex
- The parallel elastic component (PEC) contributes to potential energy storage
Phase II: Amortization (Transition)
- The critical coupling phase between eccentric and concentric actions
- Afferent nerves from muscle spindles synapse with alpha motor neurons
- Alpha motor neurons transmit signals to the agonist muscle group
- Key point: Shorter amortization phases result in more effective force coupling
Phase III: Concentric Action (Force Expression)
- Agonist muscle fibers contract forcefully
- Stored elastic energy is released from the series elastic component
- Alpha motor neurons stimulate maximal muscle fiber recruitment
- Force is expressed through acceleration or deceleration depending on the movement goal
Structural Components of Force Production
Understanding the interaction between the three main components of muscle mechanics helps clarify how reactive training works:
- Series Elastic Component (SEC): Primarily tendons and aponeuroses that store and release elastic energy like springs
- Contractile Component (CC): The actual muscle fibers that generate active force through actin-myosin cross-bridging
- Parallel Elastic Component (PEC): Connective tissues surrounding muscle fibers that contribute to passive tension
During reactive movements:
- In eccentric phases, all three components (CC, SEC, and PEC) produce or manage force
- The SEC and PEC resist elongation as the muscle lengthens
- The CC controls the speed and quality of the eccentric movement
- Less metabolic energy is required during eccentric actions compared to concentric ones
- During concentric action, the stored elastic energy in the SEC significantly contributes to force production
Neurological Enhancements
Reactive training creates several beneficial neurological adaptations:
- Increased Motor Unit Recruitment: More muscle fibers are engaged during movements
- Enhanced Motor Unit Firing Frequency: Neural signals fire more rapidly
- Improved Motor Unit Synchronization: Better coordination of muscle fiber activation
- Reduced Neural Inhibition: Decreased activity of protective mechanisms (like Golgi tendon organs) that limit force production
- Enhanced Proprioception: Improved body position awareness and coordination
Universal Applications: Not Just for Athletes
One of the most persistent misconceptions about reactive training is that it’s exclusively for athletes. In reality, reactive training is relevant for virtually every population—the implementation simply varies based on individual capacity and goals.
Consider a 75-year-old stepping off a curb and momentarily losing balance. Their ability to quickly generate force to reestablish their base of support under their shifting center of gravity could be the difference between recovery and a fall. This scenario demonstrates why rate of force development—a key training outcome of reactive work—matters for everyone.
Reactive training serves multiple essential purposes:
- Enhances the excitability and reactivity of the neuromuscular system
- Improves rate of force production (power development)
- Increases movement efficiency and economy
- Enhances joint stability through improved proprioception
- Reduces injury risk through neuromuscular training
- Improves overall movement coordination and control
Dispelling Common Myths
Several misconceptions about reactive training have persisted for decades, often repeated without scientific support:
Myth 1: “You must be able to squat 2x bodyweight before doing plyometrics”
This arbitrary threshold has been repeated for years without scientific basis. Consider the logical inconsistency: Would a 55kg woman need to squat 110kg before performing even basic reactive exercises? This would exclude most recreational trainees from beneficial training modalities. The reality is that reactive training exists on a spectrum, with appropriate entry points for all fitness levels.
Myth 2: “Children should not do reactive training”
This myth disregards basic observation: watch children at play, and you’ll see they naturally perform jumping, hopping, and bounding movements constantly. Children’s play inherently involves reactive forces. The key is not prohibition but appropriate progression and monitoring of volume and intensity.
Myth 3: “You should not perform reactive training every day”
While high-volume, high-intensity plyometric sessions should indeed be limited in frequency, low-volume reactive work can and often should be performed frequently. The principle is: frequency over volume. Small doses of reactive work performed regularly yield better adaptations than occasional high-volume sessions.
Evidence-Based Implementation Guidelines
Based on current research and practical application, consider these guidelines when implementing reactive training:
Program Design Considerations
- Progress methodically: Begin with foundational landing mechanics before advancing to more dynamic exercises
- Focus on quality: Emphasize technical execution over quantity of repetitions
- Listen to landings: Quiet landings indicate proper force absorption through muscular control; loud landings suggest excessive joint loading
- Scale appropriately: Larger individuals should use smaller obstacles and reduced impact heights
- Prioritize frequency over volume: Small doses frequently trumps occasional high-volume sessions
- Monitor fatigue: Reactive ability diminishes significantly with fatigue, increasing injury risk
- Consider movement planes: Different sports and activities require reactive ability in various planes of motion
- Apply specificity: Match reactive exercises to the demands of the target activity or sport
Exercise Selection Guidelines
- Begin with in-place exercises before progressing to moving variations
- Master bilateral exercises before advancing to unilateral challenges
- Start with vertical exercises before introducing horizontal and multi-directional movements
- Use low-intensity reactive exercises as movement preparation before strength training
- Consider sequential progressions: jump-lands → repeated jumps → depth jumps → complex combinations
Population-Specific Applications
Athletic Performance
- Sport-specific movement patterns with progressive loading
- Higher-intensity shock method techniques when appropriate
- Complex training (combining strength and reactive exercises)
- Multi-directional and variable surface training
General Fitness
- Emphasize proper landing mechanics and force absorption
- Incorporate basic reactive exercises into circuit training
- Use low-intensity reactive work for movement preparation
- Focus on functional patterns relevant to daily activities
Older Adults
- Begin with supported reactive exercises (holding rails if needed)
- Emphasize quick step reactions and balance challenges
- Include seated reactive movements when appropriate
- Progress gradually with close monitoring
Rehabilitation
- Start with isometric contractions at various speeds
- Progress to low-level reactive exercises with minimal joint stress
- Incorporate reactive stability exercises before dynamic movements
- Monitor tissue tolerance and adapt exercises accordingly
Building a Progressive Reactive Training System
A comprehensive reactive training system should progress through distinct phases:
Phase 1: Foundation
- Landing mechanics and force absorption
- Basic jumping with proper technique
- Low-intensity skipping and hopping
- Emphasis on eccentric control and stability
Phase 2: Basic Reactive Development
- Repeated jumps with minimal ground contact time
- Low-level box jumps (focusing on landing)
- Lateral bounds and linear bounds (appropriate populations only)
- Medicine ball reactive throws
Phase 3: Advanced Development
- Depth jumps (from appropriate heights)
- Single-leg reactive exercises
- Multi-directional reactive movements
- Sport-specific reactive patterns
Phase 4: Performance Specialization
- Complex combinations of reactive movements
- Sport-specific loading and environmental conditions
- Variable surface training
- Competition-specific reactive patterns
Monitoring and Assessment
To ensure appropriate progression and adaptation, regularly assess reactive ability using metrics such as:
- Jump height or distance
- Ground contact time
- Reactive strength index (jump height ÷ ground contact time)
- Force-velocity profiling
- Movement quality and technical execution
Conclusion: A Universal Training Approach
Reactive training represents a fundamental aspect of human movement that transcends age, athletic ability, or training goals. By understanding the science behind these movements and implementing a progressive, individualized approach, coaches and practitioners can safely leverage reactive training principles to enhance performance, prevent injury, and improve quality of life across diverse populations.
The key lies not in avoiding reactive training for certain groups but in appropriately scaling and applying the correct reactive training methodology for each individual—matching the exercise to the person rather than forcing the person to adapt to a rigid exercise paradigm.
The definition of a plyometric exercise are exercises where they are generally considered to have a rapid eccentric (pre-stretch) contraction followed immediately by a quick concentric contraction (Shock Method). This is known the the stretch-shortening cycle and is explain further below. The reason we choose the term Reactive over Plyometrics is due to the fact that entry level plyometric exercises may not meet the definition due to utilizing proper progressions developing the required biomechanics to safely execute plyometric exercises and includes both Shock Method and Jump Training.
True
plyometrics was first developed by Verkhoshonski and other Soviet Block scientists and was referred to as Shock Method (Verkhoshonski, 1968). The term Plyometrics was first used in 1975 by Fred Wilt (American Track & Field Coach). Wilt interpreted plyometrics as exercises that produce “an overload of isometric-type muscle action which invoke the stretch reflex in muscle”.
Some referred to Jump training as plyometrics which created further confusion as not all Jump training is plyometric in nature. In true (explosive) plyometrics the exercise must be executed as quickly as possible, in 0.15 to 0.2 seconds.
Even though Jump Training involve many of the same mechanisms as Plyometrics or Shock Method, they are very different in their effect on the body. For example, jump exercises involve the central nervous system (CNS) but not to the same extent as Plyometric exercises or Shock Method. In the latter case, the stress on the central nervous system is much greater and has a much more noticeable effect on the body. The eccentric strength component is also much less in Jump Training vs Plyometrics or Shock Method.
The term Reactive training does encompass plyometrics, utilizing the stretch-shortening cycle to enhance neuromuscular efficiency, rate of force production, and reduced neuromuscular inhibition along a continuum but this continuum also includes many techniques and principles.
Enhanced performance during functional activities emphasizes the ability of the muscles to exert maximal force output in a minimal amount of time (rate of force production). Reactive training allows you to train this ability specifically while in a controlled environment reducing injury potential in training and even during the individual maybe involved with.
Reactive Training heightens the excitability of the central nervous system, which can improve performance when implemented with the right training program and recovery.
Reactive training is important for every client, not just the athlete. The concepts of training do not change when applying reactive training to the general population only the application of the concept.
For example, if a 75 year person steps off from a curb and loses their balance, they had better have worked on rate of force production so that they can re-establish their base of support under their rapidly changing center of gravity.
Purposes of Reactive Training
- Enhance the excitability, sensitivity and reactivity of the neuromuscular system
- Enhance the rate of force production
- Increase motor-unit recruitment
- Increase motor-unit firing frequency
- Increase motor-unit synchronization
Interaction of SEC, PEC, and CC
- SEC: Series Elastic Component.
- CC: Contractile Component
- PEC: Parallel Elastic Component.
Concentric Contraction
- CC responsible for shortening muscle
- As muscle continues to shorten, stretch is applied to SEC
Eccentric Activity
- CC, SEC, and PEC produce force
- SEC and PEC resist movement as muscle elongates
- CC controls speed and quality of movement
- Less force required
- Less energy used in eccentric
Neurological Components
- Stimulation of proprioceptors and Muscle spindles
- Golgi Tendon Organ’s (GTO’s)
Phases of the Stretch-Shortening Cycle
Understanding the basics and terminology of the stretch-shortening cycle is important to be able to principles and then coach those principles using the methods here.
The term “stretch shortening cycle” is the most commonly used and perhaps most appropriate description of reactive or plyometric exercises.
Phase I (eccentric phase)- stretching the agonist muscle group(s)
- Elastic energy is stored
- Muscle spindles fire
Phase II (amortization phase)- time needed to switch from an eccentric to a concentric action
- Afferent nerves synapse with alpha motor neurons
- Alpha motor neurons transmit signal to agonist muscle group
Phase III (concentric phase)- agonist muscle fibers contract
- Elastic energy is released from the series elastic component
- Alpha motor neurons stimulate the agonist muscle group
Misinformation on Reactive Training
You may find that some information that is presented on reactive training (plyometrics) is actually incorrect and often based only on what others have stated over the year rather than real facts. Here are a few you may hear:
- You must be able to squat 2 x bodyweight.
- Kids should not do reactive training (plyometrics).
- You should not perform reactive training (plyometrics) everyday.
You must be able to squat 2 x bodyweight
The story goes that this was taken out of context in a lecture and somehow became a fact. Nothing further could be from the truth especially is you actually use some logic and look at what is being stated. A 55kg woman should only utilize reactive training only once they are able to squat a load of 110kg. How many non-powerlifting 55kg women are squatting 110kg? Just remember its about progression and there in not scientific basis for this rule.
Kids should not do reactive training
This one again makes no sense as what do you think kids do all day in they playground? Maybe not in some countries where play and physical education has been downplayed however for others you can just look at kids play is see the involvement of these reactive forces.
You should not perform reactive training everyday
This one on the surface may sound like it would be true however when it comes to reactive training its about frequency and not volume. Meaning you want lower volume reactive work performed more frequently. This is due the the potential stressors on the tissue produced when using higher volume training.
General Guidelines on Reactive Training
- Linear Bounds may only be necessary for track athletes (may cause SI or foot pain). Lateral Bounds may still be used.
- Frequency not volume is the key.
- The larger the individual the smaller the obstacle.
- Don’t use jump ropes as Reactive Training– far too repetitive.
- Listen to landing – loud means that joints take the loading, quiet means the muscles are taking the loading.