Plyometrics for beginners - basic considerations

Transcription

1 ' By I A A f Plyometrics for beginners - basic considerations Vern Gambetta ' Although plyometric training has been extensively used for the past thirty years, there is still is a widespread misunderstanding of this training method, especially as it applies to beginners. Vern Gambetta, Coaching Education Consultant to The Athletic Congress of the USA and a member of the NSA Advisory Editorial Board, examines some of the more imporlant faclors, namely training load, basic slrength and progression, that need to be considered when designing a plyometric training programme... Introduction The use of plyometric training in track and field is not a recent innovation. Even though it has recently received much attention as a training method, il has been a part of the training programmes of top athletes for over thirty years. Thanks to current research, we have a much better understanding of the elastic properties of muscle. This has permitted a more effective application of plyometrics to training. Unfortunately, in spite of our increase in knowledge, there is still misunderstanding concerning this training method, especially as it applies to beginners. In this article I will attempt to clear up some of the misunderstanding by explaining factors that will help coaches to be more effective in designing a plyometric iraining programme. Whal is plyometric training? Plyometric training is specific work for the enhancement of explosive power. It improves the relationship between maximum strength and explosive power. In most athletic events there is seldom enough time to develop either maximum strength or maximum speed. It takes 5 to 7 sec to develop maximum strength. There are few explosive/balislic movements in athlelics which take 61

2 that long. Therefore, the premium in performance is on generating Ihe highest possible force in a short period of time. With this as a goal, plyometric training has a primary role in the training programmes of both ihe beginner and the elite athlele. Plyometric training enhances the tolerance of the muscle for increased stretch loads. This increased tolerance develops efficiency in Ihe stretchshortening cycle of muscle contraction. During the stretching (eccentric lengthening) phase of muscle contraction, a greater amount of elastic energy is stored in the muscle. This elastic energy is then re-used in the following concentric contraction making that contraction stronger. The key to ihis is a short coupling time. Coupling time refers to the time it takes for the muscle to change from the legthening/yeilding phase to the shortening/overcoming work phase. This leads us to the key principle of plyometric training: The rate, not the magnitude of the stretch, is what determines the utilization of elastic energy and the transfer of chemical energy into mechanical work. The ballistic nature of all track and field events dictates that the naturally occurring phenomenon of the stretch shortening cycle be trained. In order to be most effective, plyometric training should exhibit similar patterns of: 1) motor unit recruitment, 2) temporal sequence, and 3) firing frequency to movements in the evenis (Bosco, 1982, p. 34). This is the inherent value of plyometrics as a training method. Basic considerations Plyometric iraining is a very intense high nervous system demand activity that must take into account the follow- 62 ing factors: /. Training load The prime consideration in plyometric training is the determination of the appropriate training loads. With beginners the variables of maturation and experience compound the problem. Essentially the volume of training can be high if the intensity of the plyometric activity is low. The exercises of games should be of low nervous system demand and low motor complexity. It is possible lo get a large number of contacts with minimum stress through game activities, jump rope etc. 2. Basic strength I have always taken the position that in order to begin plyometric Iraining certain basic slrength levels are necessary. The prerequisite strength levels thought to be necessary were quite high and in many cases proved to be unreasonable. 1 have altered my views on this matter based on my practical experience and the growing understanding of the physiological basis of plyometric training. This is not to say that basic slrenglh is not important, rather it is one of many factors that must be considered before beginning plyometric iraining. For youth, high strength levels are not necessary, especially considering their relatively low body weighl. The primary concern for the beginner is strength in the stabilizing muscles in order to prevent injury. This level can be determined by several simple, easily administered and interpreted lests (Table 1, on pag. 63) that look for balance and stabilization. If the alhlete is unable to satisfactorily perform these tests then he or she should begin on a remedial programme of balance and stabilization exercises to bring these up to acceptable standards before

3 incorporating plyometrics into the Iraining programme. The next concern after stabilization strength is Ihe level of eccentric strength. Eccentric strength is the limiling factor especially in more complex high volume and high intensity plyometric training. Without adequate levels of eccentric strength, rapid switching from eccentric to concentric is impossible. Research has shown that children are unable to express large amounts of eccentric force. This can be explained by the immaturity of the central nervous sysiem (CNS) and the fact thai the threshold for activation of the golgi tendon organs (GTO) is low. The net effect is that the proprioceptive feedback mechanism operates to protect the body against high stretch loads to prevent injury. This is especially true at an age when muscle and bone have not yet reached maturity. This is a key determining factor in the progression of the exercises. According to Bosco (p. 43, 1985), children are unable to tolerate "even moderate stretch loads". In Bosco's experiments this was the case in spite of the children being able to develop high levels of mechanical power from a squat jump without a counter movement. The squat jump, due to the lack of a pre-slretch, requires good concentric strength. Without sophisticated laboratory equipment available it is possible to get a good idea of the athlete's level of eccentric strength. This is done through stabilization jump tests (Table 2, on pag. 64) and observation of the execution of basic jumping exercises. If upon observation you see an excessively long amortization phase and a slow switching from eccentric to concentric work then eccentric strength levels are not adequate and the training should be very low in volume and intensity. The specific goal should be lo raise the level of eccentric strength to an acceptable level. 3. Skill Proper execution of the exercises must be continually stres.sed at all levels. It is important for the beginner to establish a sound technical base upon which to build the higher intensity work. Movement is a constant interchange between force production and Table I - Balance and Slabiiization Tests (Klatt 1988) (All lests are perrormed without shoes to test the stabilizers of the foot). Static Stand (Hip Flexed) - Appropriate for use with all ages, a) Stand erect on one t'ooi. h) F'lex the hip and bend the knee of the non supporting leg. c) Hold this po.sition for ten seconds. d) Observe ihe ability to hold the position with as little shaking or lateral deviation as possible. Single Leg Squat - Appropriate for use with all ages. a) Squat bending al ihc ankle, knee, and hip. b) Hold lowest possible position for ten seconds. c) Observe the ability to hold the posiiioii with as little shaking or lateral deviaiion as possible. 63

4 force reduction leading to a summation of forces utilizing all three joints of the lower body: the hip, knee, and ankle. The liming and coordination of all limb segments will yield a positive ground reaction force which results in a high rate of force production. Table 3 will help give the coach a checkpoint guide for skill analysis. The key element in the execution of proper technique is the landing phase. Contrary lo popular opinion, the shock of landing is nol absorbed exclusively wilh the foot, rather it is a combination of the ankle, knee, and hip joints working together lo absorb ihe shock of landing and then transfer that force. The proper utilization of all three joints will allow the body lo use the elasticity of the muscles to absorb the force of landing and then utilize that force in the subsequent movement. This is nol to minimize the importance of the foot strike. The foot strike is on the full foot in order lo use the fool to help absorb the shock. It is incorrect to land either completely on the heel or on the ball of the foot. This type of landing will transfer high impact forces through the bone and the ankle and knee joints rather than allowing the muscle to absorb the shock. The athlete should react to the ground as if the ground is hot to emphasize optimum quickness off the ground. If the athlete is making loud slapping noises on landing this is a clue that the technique is incorrect and the exercise should stop. The feeling should be like a stone skipping across the water. In two fool contacts a good cue is to jump off the ground, not onto the ground. Upright carriage of the torso is necessary in order to ensure proper projection of the cenire of mass and avoid undue strain on the lower back. Table 2 -.Slabiiization Jump Tesls (Klatt 1988) (All jumps are performed without shoes to test the stabilizers of the foot). 64 Hop for Distance - Appropriate for use with all ages. a) Hop maximum distance. Hold the landing (like a gymnastics landing) for ten seconds. b) Compare the distance achieved with the right and left legs. c) Check the ability to hold the landing position for ten seconds. d) Check if the alhlete lands bending at ihe ankle/knee/and hip using all three joints. Hop Down (Off 12 inch box) - Only use with more mature alhletes. a) Hop off the box tor maximum distance. Hold the landing (like a gymnastics landing) for ten seconds. b) Compare the distance achieved with the right and left legs. c) Check the ability to hold the landing position for ten seconds. d) Check if the athlete lands bending at the ankle/knee/and hip using all three joints. Repetitive Jump Test (maximum effort jumps) al Jump up and down as rapidly as possible for 30 seconds. b) Observe how rapidly the athlete can switch from eccentrics (down) to concentric (up). An excessively long switching time indicates a poor level of eccentric strength. c) Observe how much the athlete deviates from the original starting position. Deviation indicates poor balance and stabilization. d) Count the number of jumps.

5 Table 3 - Jumping Skill Checkpoints Posture Head Posiiion Torso Position Foot Strike Full Foot Ball Of Foot Flat Foot Landing Quiet Loud/Slapping Leg Action Amplitude Synchronization Arm Action Coordinated Uncoordinated Correct postural alignment is directly related to core (torso) strength. If the athlete is having problems holding the torso erect during the movements then this problem should be addressed immediately through a core strengthening programme. This programme should consist of exercises to strengthen the abdomen and the spinal erector muscles as well as the rotational muscles of the trunk. The arms make a significant contribution both in terms of balance and in force production. Proper use of the arms can contribute up to 10% to the jump. The main objective for the beginner is lo learn to use the arms in opposition to the legs. In addition, it is important to learn to use the arms to transfer momentum. It has been my experience Ihat the torso position and the synchronization of the arms are the aspects of technique which are most difficult for the beginner to master. Solomavor (CUB)

6 4. Progression Appropriate beginning activities include such activities as jump rope, hopscotch, sack races, various jumping and hopping relays. Double leg takeoffs are preferable to single leg takeoffs at the beginning stages. The amplitude of the movements should increase as the level of mastery of the exercises increases. It is of paramount importance that there be continual emphasis on coordination and reinforcement of correct motor patterns. The progression in teaching and training is: 1) Landing To emphasize proper foot strike, use of ankle/knee/hip, and body alignment. 2) Stabilization Jumps To reinforce correct landing technique and raise levels of eccentric and stabilization strength. 3) Jumping up To teach the takeoff action and the use of the arms. 4) In Place Bouncing Movemenis To teach quick reaction off the ground and vertical displacement. 5) Short Jumps To teach horizontal displacement. 6) Long Jumps To add more horizontal velocity. 7) Shock Jumps High nervous system demand. Inappropriate for the beginner. Conclusion Plyometric training has tremendous potential as a training melhod for all events. Improperly introduced and taught it is a high risk/low return training activity. To optimize the returns it is necessary to follow the general guidelines set out in order to make it a low risk/high return activity. D 66 REFERENCES BOSCO. C; Stretch-Shortening Cycle in Skeletal Muscle Function and Physiological Considerations on Explosive Power in Man, Atleticastudi, , pp GAMBETTA, V.: Principles of Plyometric Training. Track Technique. Fall. 1987, pp KLATT. L., Director of Physical Performance Laboratory. Concodia College. River Forest. Illinois: Personal conversation on balance and stabilization tesling. LUNDIN. P.: Plyometric Loads for Youths and Beginners. Track Technique, 101, 1987, pp SCMIDTBLEICHER, D.: Slrength Training, Part I - Classification of Meihods, Sports, Coaching Association of Canada, Aug SCMIDTBLEICHER. D.: Strength Training. Part II - Structural Analysis of Motor Strength Qualities and its Application lo Training, Spons. Coaching Association of Canada, Sept