Plyometric training uses the acceleration and deceleration of bodyweight as the overload in dynamic activities. The dynamic activities often used are depth jumping and bounding. This training method is seen to improve muscular speedstrength (power) thereby enhancing dynamic competitive performance such as jumping (Bosco et al., 1982).
Plyometric training have been used as resistance training to improve jumping powers in many Eastern Bloc countries for at least over twenty years (Duda, 1988). During the 1960s, Yuri Veroshanki a Russian athlete coach, used plyometric training methods with much success for athletes involved in jumping events.
Plyometric again became the focus during the 1972 Munich Olympics when the Russian Valery Borzoc won the 100m in 10.0 second and also won the 200m sprint event. Much of ValeryÊs success was attributed to the use of plyometric training methods. These incidents supporting the use of plyometric training methods have been confirmed by research. Reseach has demonstrated that plyometric training methods were efficient at increasing muscular power and performance (Bosco et al., 1982; Hakkinen et al., 1992).
Coaches and athletes maintain that plyometric training represents the bridge between strength and power and perceived plyometric training as a method of training that will directly enhance competitive performance (Chu, 1992). Coaches and athletes see that weight training increases strength and plyometric and this is also seen as a means of being able to apply this strength to improve performance. This perception is well supported by many studies reporting that the combination of weight training and plyometric resulted in superior performance gains as compared to plyometric or weight training alone. Adams et al., (1992) reported that six weeks of resistance training resulted in 3.3cm increase in vertical jump when using weight training, a 3.81cm increase when using plyometric training, and a 10.67cm increase in vertical jump when a combination of weight training and plyometric training techniques were employed.
ADVANTAGES OF PLYOMETRIC TRAINING
Plyometric ia a relatively new form of dynamic action resistance training, or jumping training, which became popular during the late 1970s and early 1980s for improving jumping performance. It is proposed to bridge the gap between speed and strength training.
Plyometric uses the stretch reflex to facilitate recruitment of additional motor units. It also loads both elastic and contractile components of the muscles. As an example, to develop knee extensor muscle strength, you jump from a 46cm (18- inch) box to the ground, land with your knees partly flexed, then rebound upward by a forceful maximum contraction of your knee extensor muscles.
Examples of Plyometric Exercise;
- Use a 15 cm to 30 cm high box, start standing to the side of the box.
- Place the foot closest to the box on top. Use the leg on the box to raise the body until the leg is extended, then lower to the starting position.
- Do not push off the foot on the ground; use the bent leg to do all the work.
- Perform the exercise using both of your leg
One-Foot Zig-Zag Hops
- Use two parallel lines, 60 cm to 107 cm apart and 10m long, start balanced on one foot on a line.
- Jump from one line to the other in a continuous forward motion for 10m, always taking off and landing on the same foot.
- Do not double hop at the touchdown.
- Perform the exercise on each of your foot.
Lateral High Hops
- Use a 30 cm to 60 cm high box.
- Start standing to the side of the box with the left foot raised onto the middle of the box.
- Using a double arm swing, jump up and over the other side of the box, landing with the right foot on top of the box and the left foot on the floor.
- This drill should be done in a continuous motion, shuffling back and forth across the box.
Two-Foot Zig-Zag Hops
- Use two parallel lines, 60 cm to 107 cm apart and 10 m to 15 m long.
- Start with feet shoulder width apart, straddling a line.
- Jump from one line to the other in a continuous forward motion.
Plyometric training involves a number of advantages over traditional heavy weight training methods. These include :
- Plyometric exercise tends to be performed in a more explosive way than traditional weight training. A depth jump will be performed in 300-500 cm., whereas a heavy squat may take several seconds to perform. Thus plyometric training requires the athlete to rapidly develop force, promoting the development of muscular power. Hakkinen et al. (1985) reported that the dynamic nature of plyometric training allows for greater improvements in the maximal rate of force development and thus power, in comparison to traditional weight training methods.
- Plyometric exercises do not involve a deceleration phase, as seen in traditional weight training, as the movement does not have to achieve zero velocity at the end of the exercise. Plyometric exercises involve the production of high forces and accelerations throughout the entire range of motion, specific to most competitive movements.
- Plyometric exercises are performed at higher velocities than those achievable using traditional weight training. This can increase the velocity to enhance the specificity of this training modality to compatitive performance improving the transference of training gains to the competitive situation.
- Plyometric exercises involves a dynamic stretch-shorten cycle movement similar to that adopted in most sporting actions. Research has shown that the plyometric exercise promotes the ability to utilise the stretch-shorten cycle by enhancing the use of elastic energy and the stretch reflex (Bosco et al., 1982; Van Leemputte et al., 1983; Schmibtbleicher et al., 1988).
Disadvantages of Plyometric Training
This training modality is a relatively recent phenomenon especially to Malaysians). Despite the above advantages of plyometric training it has a number of limitations associated with its use. These are:
- Due to the dynamic nature of plyometric exercises, high impact forces can occur when landing from activities such as depth jumping or bounding. The impact force of about three to four times the body weight are not uncommon when performing high intensity plyometric training. Hence, these high tension forces placed on the musculoskeletal system can result in injury such as shin splints or even stress fractures. The occurence of injury is reduced if the individual has a relatively high level of strength prior to performing these plyometric exercises. Landing on a compliant surface, such as rubber matting, cuckoo mats, using shock absorbing shoes will assist in reducing impact forces. Impact forces can also be dissipated over a relatively long period of time distance by using appropriate landing strategies. Such a strategy is realised during landing when the individual absorbs the impact by flexing about the knees and ankles and allowing the body to "give a little" upon initial impact.
- There is a limited range of exercises for plyometric training. Most plyometric activities are essentially limited to the lower body and dominated by muscular actions involving extension about the hip and the knee joints. Upper body activities utilising medicine balls are typically performed with such a low loading as to represent very low level of overload to the musculature.
- Due to relatively high velocities achieved when doing the plyometric training, the forces produced during these exercises tend to be lower than those achieved during traditional weight training. Therefore, plyometric training does not develop muscular strength as well as traditional weight training.
Strength development is essential prior to high intensity plyometric training such as depth jumping. Without a good strength base, the legs or arms will not be able to withstand the extreme forces generated by plyometric. Without this strength base, one is prone to injury.
There is a high relationship between strength and power so that one cannot have a high degree of power without first being relatively strong. The current level of strength will represent the upper limit to oneÊs power potential. Long strength training is needed. Before doing the high impact activities such as high depth jumps, the athlete should be able to squat at least 1.5 times his body weight (Roundtable NSCA, 1986).
Use the same principles of training for weight training and plyometric trainings. The principle of overload, specificity, variation, recovery are as applicable to plyometric training as they are to strength training. The load placed on the system, while using the plyometric exercises, should be progressively increased.
This is achieved by increasing the height of the drop and/ or the addition of extra load through the use of weight belts/ vest and shoes. In a study by Wilson et al., subjects completed 10 weeks of plyometric training programme that involved two weekly plyometric sessions of progressively increasing drop heights and sets. Subjects were thoroughly prepared prior to training and had performed tradional weight training for at least a year prior to the plyometric training programme. Throughout the training sessions, body mass (weight) was used as the load.
If an athlete experiences soreness in the shins or other skeletal structures it is generally caused by too great a loading or too soon into the training cycle. If that is the case, the drop heights should be lowered and/or the weight carried by the
- Plyometric exercises are designed to build muscular speed-strength. This can be accomplished by applying the principles of PRE to an exercise that begins with a maximum stretch and ends in a quick powerful contraction in one plane of motion.
- Optimal drop height - Uses the height which results in the greatest rebound height. Based on individual differences, the height is generally between 0.3m to 0.7m high.
- Ground contact time - Ground contact time or time in contact with a medicine ball, must be as short as possible and must rebound very quickly.
- Rest and recovery - The plyometric training must be done explosively and thus athletes need to be in a fresh state. Plyometric should be performed prior to fatigue activities, such as weight training. Relatively long rest periods, of about 5 minutes, should be imposed between repeated plyometric activities to enable full recovery of the neuromuscular system. This will ensure that the athletes keep performing in a very dynamic fashion.
- Feedback - If the exercise consists of vertical jumping the height reached must be told so that this will motivate the athletes.