National Academy of Sports Medicine Integrated Reactive (Plyometric) Training Integrated Reactive Training Copyright © 2008 National Academy of Sports Medicine Printed in the United States of America All rights reserved. Except for use in a review, the reproduction or utilization of this work in any form or any electronic, mechanical, or other means, now known or hereafter invented, including xerography, photocopying, and recording, and in any information-retrieval system is forbidden without the written permission of the National Academy of Sports Medicine. Distributed by: National Academy of Sports Medicine 26632 Agoura Road Calabasas, CA 91302 800.460.NASM Facsimile: 818.878.9511 http: www.nasm.org Author: Dr. Micheal Clark, DPT, MS, PES, CES Integrated Reactive Training Introduction The demands imposed during training must reflect those incurred during advanced phases of rehabilitation, reconditioning, and training. This is referred to as the specificity of training concept.1 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). Success in most functional activities depends on the speed at which muscular force is generated. Power and reactive neuromuscular control represent a component of function and are perhaps the best measure of success in activities that require rapid force production. Reactive training utilizes the stretch-shortening cycle (integrated performance paradigm) to enhance neuromuscular efficiency, rate of force production, and reduced neuromuscular inhibition. Reactive training heightens the excitability of the central nervous system, which improves performance. This course reviews the various components of reactive training so that the health and fitness professional understands how to incorporate reactive training into an integrated training program. Section I: Section II: Section III: Section IV: Section V: Section VI: Section VII: Appendix References The Definition and Purpose of Reactive (Plyometric) Training The Three Phases of Reactive Training Physiological Principles of Reactive Training Proposed Mechanisms by Which Reactive Training Enhances Performance Scientific Rationale for Reactive Training Reactive Training Program Summary The speed of muscular exertion is limited by neuromuscular coordination. This means that the body moves only within a range of speed set by the central nervous system.4 Optimum performance depends on the speed at which muscular forces can be generated. It is generally accepted that optimum performance in sports and other functional activities requires both technical skill and power. Skill is the ability of the neuromuscular system to coordinate the kinetic chain to allow for quick and accurate movements in all directions. Power is the ability to exert maximal force in the shortest amount of time. Power is most efficiently increased through a combination of an increase in the amount of force that the muscle can produce and a decrease in the amount of time taken to produce that force. 5 As described in this manual’s final section, reactive training utilizes a three-level training program to improve both neuromuscular efficiency and the range of speed set by the central nervous system. Integrated Reactive Training Figure 1: Skill and Power SKILL is the ability of the neuromuscular system to coordinate the kinetic chain to allow for quick and accurate movements in all directions. POWER is the ability to exert maximal force in the shortest amount of time. Integrated Reactive Training Section I: The Definition and Purpose of Reactive (Plyometric) Training Reactive (plyometrics) training is defined as a quick, powerful movement involving an eccentric contraction followed immediately by an explosive concentric contraction.2 This defines a stretch-shortening cycle or an eccentric-concentric coupling phase. Reactive training exercises stimulate the body’s proprioceptive mechanism and elastic properties to generate maximal force output in the minimal amount of time.2 Figure 2: Purpose of Reactive Training m Enhance the excitability, sensitivity, and reactivity of the neuromuscular system m Enhance the rate of force production m Increase motor unit recruitment m Increase motor unit firing frequency m Increase motor unit synchronization Reactive training enhances motor learning and has five distinct purposes: to enhance the excitability, sensitivity, and reactivity of the neuromuscular system; to enhance the rate of force production; to increase motor unit recruitment; to increase motor unit firing frequency; and to increase motor unit synchronization. Maximal sensorimotor integration allows for the development of complex motor programs. Reactive training also enhances muscular function and optimizes the appropriate activation of prime movers and synergists. In addition, reactive training causes reciprocal inhibition of antagonists, as demonstrated by the ability to perform complex, explosive movements. Reactive training optimizes neuromuscular efficiency by enhancing motor unit recruitment, increasing motor unit firing frequency, enhancing firing patterns for specific functional patterns, and improving motor unit synchronization at lower force outputs. All movement patterns that occur during functional activities involve a series of repetitive stretch-shortening cycles modeled in the integrated performance paradigm. Integrated Reactive Training Figure 3: Integrated Performance Paradigm %CCENTRIC&ORCE2EDUCTION #ORE3TABILIZATION .EUROMUSCULAR3TABILIZATION #ONCENTRIC&ORCE0RODUCTION As illustrated in Figure 3, the integrated performance paradigm includes eccentric deceleration, isometric stabilization, and concentric acceleration. The health and fitness professional must use specific functional exercises to adequately prepare the client to return to the rigors of his or her specific activity.6,7,8 Traditional training, reconditioning, and rehabilitation in which heavy loads are emphasized induce greater hypertrophy and increases in strength, but may not effectively improve maximal power output, functional strength, or neuromuscular efficiency.9 One of the most remarkable aspects of skeletal muscle is its adaptive potential. If a muscle is systematically and functionally stressed, it will allow continual adaptation and optimum performance. A baseball pitcher utilizes the integrated performance paradigm to produce maximal explosive concentric contractions. To replicate these forces during training, reconditioning, and rehabilitation is beyond the scope of traditional training. For example, the Cybex 6000 reaches maximal angular velocities of 500 to 600 degrees per second, which is nonspecific to the greater than 7,000 to 10,000 degrees per second of shoulder angular velocity during baseball pitching.10 Consequently, specific functional exercises should be an integral component in every training, reconditioning, and rehabilitation program to facilitate a complete functional return and allow optimum performance. The health and fitness professional should utilize reactive training to replicate the explosive muscular contractions that occur during most functional movements. Integrated Reactive Training The neuromuscular system must react quickly following an eccentric contraction to produce a concentric contraction and impart the necessary force (acceleration) in the appropriate direction. Muscles produce the necessary change in the direction of the object’s center of mass.4 Specific functional exercises that emphasize a rapid change in direction must be utilized to prepare each client for the functional demands of his or her specific activity. Reactive training provides the ability to train specific movement patterns in a biomechanically correct manner, thereby more functionally strengthening the muscle, tendon, and ligaments. The ultimate goal of reactive training is to decrease the amount of time between an eccentric contraction and a concentric contraction. 5 Integrated Reactive Training Section II: The Three Phases of Reactive Training There are three phases involved in reactive training: the eccentric phase, the amortization phase, and the concentric phase. Figure 4: Phases of Reactive Training THREE PHASES OF REACTIVE TRAINING m Eccentric Phase m Amortization Phase m Concentric Phase The Eccentric Phase This phase increases muscle spindle activity by prestretching the muscle prior to activation.11,12 Potential energy is stored in the elastic components of the muscle during the force-reduction phase. Prolonged loading prevents optimum exploitation of the myotatic stretch reflex.13,14 The Amortization Phase This phase involves dynamic stabilization and is the amount of time that elapses between the eccentric contraction (force reduction) and the initiation of the concentric contraction (force production).2 The amortization phase is also referred to as the electromechanical delay between the eccentric and concentric contraction, during which the muscle must switch from overcoming force to imparting the force in the intended direction.4 A prolonged amortization phase results in less than optimum neuromuscular efficiency secondary to a loss of elastic potential energy. The more rapidly an individual switches from an eccentric contraction to a concentric contraction, the more powerful the response.2 The Concentric Phase This phase involves force production and results in enhanced muscular performance following the eccentric phase of muscle contraction. Integrated Reactive Training Section III: Physiological Principles of Reactive Training Reactive training utilizes the elastic and proprioceptive properties of a muscle to generate maximum force production (reference the integrated performance paradigm). 2 Reactive training stimulates the body’s mechanoreceptors to facilitate an increase in muscle recruitment over a minimal amount of time.2 Mechanoreceptors are specialized sensory neurons located within the muscle that provide information to the central nervous system as to the degree of muscular distortion. The central nervous system then uses this sensory information to influence muscle tone, motor execution, and kinesthetic awareness.12 Stimulation of these receptors can cause facilitation, inhibition, and modulation of both agonist and antagonist muscle activity. This enhances neuromuscular efficiency and functional strength. Muscle spindles and Golgi tendon organs (GTO) provide the proprioceptive basis for reactive training.9,15,16,17,18 The Elastic Properties of Muscle Several authors19,20,21,22 have reported that an eccentric contraction immediately preceding a concentric contraction significantly increases the force generated concentrically as a result of the storage of elastic potential energy. During the loading of the muscle, the load is transferred to the elastic components (parallel elastic elements and series elastic elements) and stored as elastic potential energy. The elastic elements then contribute to the overall force production by converting the stored elastic potential energy to kinetic energy, which is then utilized to enhance the contraction.19,21,23 The muscle’s ability to use the stored elastic potential energy is affected by the variables of time, magnitude of stretch, and velocity of stretch. Increased force generation during the concentric contraction is most effective when the preceding eccentric contraction is of short range and is performed without delay.17 Integrated Reactive Training Figure 5: Elastic Properties of Muscle The improved muscular performance that occurs with the prestretch in a muscle is the result of the combined effects of both the storage of elastic potential energy and the proprioceptive properties of the muscle.19,20,24 The percentage that each component contributes is unknown.20 The degree of enhanced muscular performance is dependent upon the time elapsed between the eccentric and the concentric contraction.24 Integrated training enhances overall kinetic chain neuromuscular efficiency. Training that enhances neuromuscular efficiency decreases the time elapsed between the eccentric and concentric contraction, thereby improving performance. 10 Integrated Reactive Training Section IV: Proposed Mechanisms by which Reactive Training Enhances Performance There are three proposed mechanisms by which reactive training improves performance: enhanced muscle spindle activity, desensitization of the GTO, and enhanced intramuscular and intermuscular neuromuscular efficiency. Figure 6: Reactive Training and Performance Enhancement PROPOSED MECHANISMS BY WHICH REACTIVE TRAINING IMPROVES PERFORMANCE: m Enhanced muscle spindle activity; desensitization of the GTO m Enhanced intramuscular neuromuscular efficiency m Inter-muscular neuromuscular efficiency Enhanced Muscle Spindle Activity The speed of a muscular contraction is limited by the neuromuscular system. The kinetic chain will move only within a set speed range, regardless of how strong a muscle is.2 The faster a muscle is loaded eccentrically, the greater the concentric force production.12 Figure 7: Muscle Spindle 11 Integrated Reactive Training Desensitization of the Golgi Tendon Organ Desensitizing the GTO increases the stimulation threshold for muscular inhibition, ultimately allowing increased force production with a greater load applied to the musculoskeletal system.2 Figure 8: GTO Enhanced Neuromuscular Efficiency Reactive training may promote changes within the neuromuscular system that enable the individual to have better neuromuscular control of the contracting agonists and synergists, thus enabling the central nervous system to operate more automatically.4 These neural adaptations lead to enhanced neuromuscular efficiency even in the absence of morphological adaptations. Exploiting the stretch reflex, inhibiting the GTO, and enhancing the ability of the nervous system to react with maximum speed to the lengthening muscle optimizes the force produced by concentric contraction. 12 Integrated Reactive Training Section V: Scientific Rationale for Reactive Training Numerous studies have shown the benefits of implementing an integrated reactive training regimen, ranging from decreases in injury to increases in strength and endurance. Chimera et al. showed that a six-week plyometric training program improved hip abductor and adductor coactivation ratios to help stabilize the knee during landing.25 A study by Wilkerson et al. of 19 female basketball players showed an improved hamstring-to-quadriceps ratio, theorized to improve dynamic knee stability during the eccentric deceleration phase of landing.26 Irmischer et al. showed that a knee ligament injury-prevention program implementing progressive plyometric training reduced landing forces thought to help prevent knee injuries.27 In addition, Hewett et al. demonstrated decreased peak landing forces, enhanced muscle balance ratio of the hamstrings and quadriceps, and a decrease in anterior cruciate ligament injuries in female soccer, basketball, and volleyball players when a reactive neuromuscular (plyometric) training program was implemented.28 Beyond injury prevention, plyometric training has been shown to increase strength and power. In a study by Markovic et al., a 10-week plyometric training program increased leg power and performance. It increased squat jump height 6.5% and countermovement jump height 6.3%. 29 Hoffman et al. determined that a loaded squat-jump training program improved one repetition maximum in squats and power clean strength. The eccentrically loaded squat jump was theorized to be the catalyst for the strength improvements shown.30 Of special interest is the study by Spurrs et al., which demonstrated that incorporating a plyometric training program increased countermovement jump height, decreased 3K run time, and increased running economy. 31 These improvements in performance were attributed to increased musculotendinous stiffness as a result of implementing a reactive neuromuscular (plyometric) training program. 13 Integrated Reactive Training Section VI: Reactive Training Program An effective reactive training program has several fundamental requirements: adequate functional strength, adequate kinetic chain structural and functional efficiency, and adequate stabilization strength. Specificity For optimum carryover, there should be a high degree of similarity between the training activity and the functional activity. By performing reactive training during integrated movement patterns, the exercise has specific physiological, biomechanical, metabolic, and neuromuscular carryover. 32,33,34 Adequate Functional Strength A greater functional strength base and greater neuromuscular efficiency allow greater force production, thus resulting in optimum performance. Optimum levels of functional strength and neuromuscular efficiency allow optimum eccentric, isometric, and concentric contractions during integrated movement patterns (muscle contraction spectrum). Optimum eccentric neuromuscular control allows for more efficient use of stored elastic potential energy, and a greater concentric contraction. Adequate Stabilization Strength High levels of isometric stabilization strength and neuromuscular efficiency decrease the amortization phase. This decreases the amount of time elapsed between the eccentric contraction and the concentric contraction, resulting in decreased tissue overload and decreased potential for injury. A reactive training program is an essential component for all integrated training programs. The key to an effective, integrated reactive training program is the design and implementation of the program. Each program should be progressive, systematic, multiplanar, and activity specific. Reactive Training Criteria Each individual must be thoroughly screened prior to beginning a training program. The individual must have an unremarkable medical history. The individual must receive a thorough kinetic chain assessment that includes a review of the following: posture, gait, muscle balance, core, neuromuscular control and function. 14 Integrated Reactive Training Reactive Training Assessment To establish a baseline measurement, it is important to assess an individual’s power production and neuromuscular control prior to initiating an integrated training program. The health and fitness professional can use the vertical jump test (Figure 9) and the shark skill test (Figure 10) to assess power and reactive neuromuscular control, respectively. Figure 9: Vertical Jump Test 15 Integrated Reactive Training Figure 10: Shark Skill Test Safety Requirements Each individual should have supportive shoes, access to a resilient training surface, a proper program, and knowledgeable supervision prior to beginning a reactive training program. 5,35 Training Variables An integrated, reactive training program can be varied like other components of an integrated training program. Training variables that can be manipulated include plane of motion, range of motion, external load, amplitude of movement, contraction velocity, muscle action, duration, intensity, and frequency. 16 Integrated Reactive Training Training Progression The training program proceeds from simple to complex, stable to unstable, body weight to extra resistance, and low load to high load, and includes proper utilization of the plyometric stress continuum. Intensity The intensity of the exercise is controlled by the selection of the exercise. For example, a two-leg squat jump is less intense than a one-legged hop. Intensity is also controlled by the use of external load and manipulating the duration, rest periods, and frequency of the exercise. Overtraining Overtraining is a pathological state that results from cumulative neuromuscular and metabolic fatigue. Signs of overtraining include prolonged foot contact, lack of neuromuscular control, decreased vertical height or horizontal displacement, and longer rest periods.11 NASM has designed a systematic, progressive, and integrated balance training program utilizing the Optimum Performance Training (OPT) model. The program includes three phases: Level 1, Stabilization; Level 2, Strength; and Level 3, Power. Figure 11: OPT Model 17 Integrated Reactive Training Reactive Stabilization In reactive-stabilization training, exercises involve little joint motion. They are designed to establish optimum landing mechanics, postural alignment, and reactive neuromuscular efficiency. When an individual lands during these exercises, he or she should hold the landing position for 3–5 seconds before repeating. Box Jump Up w/Stabilization – Front 1 Box Jump Up w/Stabilization – Front 2 Box Jump Up w/Stabilization – Side 2 18 Box Jump Up w/Stabilization – Side 1 Box Jump Up w/Stabilization – Turning 1 Box Jump Up w/Stabilization – Turning 2 Integrated Reactive Training Box Jump Down w/Stabilization – Front 1 Box Jump Down w/Stabilization – Front 2 Box Jump Down w/Stabilization – Side 2 Box Jump Down w/Stabilization – Side 1 Box Jump Down w/Stabilization – Turning 1 Box Jump Down w/Stabilization – Turning 2 19 Integrated Reactive Training Squat Jump w/Stabilization 1 Squat Jump w/Stabilization 2 Horizontal Jump w/Stabilization 1 20 Squat Jump w/Stabilization 3 Horizontal Jump w/Stabilization 2 Horizontal Jump w/Stabilization 3 Integrated Reactive Training Reactive Strength In reactive-strength training, exercises involve more dynamic eccentric and concentric movement through a full range of motion in a more repetitive fashion (little time on the ground). The specificity, speed, and neural demand are also progressed in this level. These exercises are designed to improve dynamic joint stabilization, eccentric strength, rate of force production, and neuromuscular efficiency of the entire kinetic chain. Repeating Squat Jumps 1 Repeating Squat Jumps 2 Repeating Butt Kicks 1 Repeating Tuck Jumps 1 Repeating Butt Kicks 2 Repeating Tuck Jumps 2 Power Step Ups – Power Step Ups – Front 1 Front 2 21 Integrated Reactive Training Reactive Power In the power level of reactive training, exercises involve the entire muscle action spectrum and contractionvelocity spectrum used during integrated, functional movements. These exercises are designed to improve the rate of force production, eccentric strength, reactive strength, reactive joint stabilization, dynamic neuromuscular efficiency, and optimum force production. They are performed as fast as possible. Squat Thrusts 1 Squat Thrusts 2 Squat Thrusts 4 22 Squat Thrusts 5 Squat Thrusts 3 Integrated Reactive Training Proprioceptive Plyometrics Proprioceptive Plyometrics Proprioceptive Plyometrics Front to Back 1 Front to Back 2 Front to Back 3 Proprioceptive Plyometrics Proprioceptive Plyometrics Proprioceptive Plyometrics Side to Side 1 Side to Side 2 Side to Side 3 Proprioceptive Plyometrics Proprioceptive Plyometrics Proprioceptive Plyometrics Diagonal 1 Diagonal 2 Diagonal 3 23 Integrated Reactive Training Ice Skaters 1 Ice Skaters 2 Integrated Reactive Training Program Design OPT™ Level Stabilization Phase 1 Example Balance Exercises *0–2 Reactive Stabilization Sets/Reps Rest 1–3 x 5–8 0–90 s 2–3 x 8–10 0–60 s 2–3 x 8–12 0–60 s Box Jump Up w/Stabilization Box Jump Down w/Stabilization Squat Jump w/Stabilization Strength 2, 3, 4 **0–4 Balance Strength Repeating Squat Jump Repeating Butt Kicks Repeating Tuck Jumps Power Step Ups Power 5 ***0–2 Balance Power Squat Thrusts Ice Skaters Table 1 – Integrated Balance Training Program Design *Reactive exercises may not be appropriate for an individual in this phase of training if he or she does not possess the appropriate amount of core strength and balance capabilities. **Due to the goal of certain phases in this level (hypertrophy and maximal strength), reactive training may not be necessary. ***Because one is performing reactive/power exercises in the resistance training portion of this phase of training, separate reactive exercises may not be necessary. 24 Integrated Reactive Training Section VII: Summary Reactive training is an important component of all integrated training programs. All functional activities require efficient use of the integrated performance paradigm. Therefore, all programs should include reactive training to enhance neuromuscular efficiency and prevent injury. The kinetic chain responds to the imposed demands of training. Less than optimum results will occur if the training program does not systematically and progressively challenge the neuromuscular system. 25 Integrated Reactive Training Appendix: Integrated Reactive Training Parameters 1. Safety Requirements a. Proper core and balance capabilities b. Supportive shoes c. A resilient training surface d. A proper program e. Knowledgeable supervision prior to beginning a reactive training program 2. Training Variables a. Plane of motion b. Range of motion c. External load d. Amplitude of movement e. Muscle action f. Duration g. Intensity h. Frequency i. Contraction velocity 3. Training Progression a. Simple to complex b. Stable to unstable c. Body weight to extra resistance d. 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