Premature plyometric training may cause injury because plyometrics place considerable stress on the body. Plyometrics is an advanced training technique that should only be performed under the guidance of those with knowledge and experience with this type of training. It involves explosive types of activities (i.e., jumping onto and down from objects, bounding up and down stairs on one or both feet and high speed sending and receiving) to convert muscle strength to muscle power. Whenever you run, jump, catch or throw, you are performing a plyometric movement.
Box Jump Side Cone Jumps
Plyometric exercises train the muscles to reach maximal strength in the shortest time possible. In other words, muscle strength plus speed equals muscle power. The rapid application of force is the goal of plyometric training. Plyometric exercises will not train an energy system as seen with aerobic or strength conditioning; rather such exercises train the neuromuscular system so that it may respond more quickly to increased loads. By making use of the inherent elasticity of the muscles and certain neuromuscular reflexes, plyometric exercises enhance the speed and distance an object moves (e.g., your body, shot put).
Plyometric training is very intense, highly specific, and if done improperly it may be injurious.
How Plyometrics Work
Plyometric exercises help to develop explosive strength and speed in fast twitch muscle fibers. Those exercises use the inherent stretch-recoil properties of muscle (i.e., eccentric tension generated when the muscles are lengthened) to enhance subsequent shortening or concentric contractions. This is the dynamic action behind the rapid pre-stretch or “cocking” phase to “activate” these natural recoil properties. Examples of this phase include taking the arm back into position prior to throwing a baseball or bending the knees prior to jumping. Thus athletes that rely on explosive strength and speed, such as sprinters and basketball players, include plyometrics in their training programs. A plyometric movement can be broken down into three phases:
♦ Lengthening phase {eccentric contraction)
♦ Amortization phase
♦ Take-off (concentric contraction)
There are three phases of Plyometrics: Lengthening, Amortization and Take-Off
During the lengthening phase, the muscle creates tension like a spring being stretched. This type of contraction, called an eccentric contraction, occurs when performing movements such as jumping flown from an object, running downhill, or lowering a weight.
After contraction, tension is built into the muscle as it lengthens. The take-off occurs via concentric contraction of the muscles. During this phase, the muscle shortens as it contracts, and actual work (i.e., movement of the body through space) is performed.
The amortization phase is the period of time from the beginning of I he lengthening phase to the beginning of the take-off phase. This is the most important phase when it comes to plyometric training. During this phase, the muscle must convert the muscular tension generated during the lengthening phase to acceleration in a selected direction during the takeoff phase. The elastic properties inherent within the muscles and neuromuscular reflexes (the stretch reflex) arc responsible for this conversion. Plyometric training may increase the efficiency of this conversion. The goal of plyometric training is to decrease the amount of time in the amortization phase and thereby increase speed.
Preparation for Plyometric Training
Plyometric exercises should he undertaken only once an adequate strength base has been developed. Most sources define an adequate strength base for lower body plyomctrics as the ability to squat or leg press 1.5 to 2.0 (imes your body weight for one maximum repetition. Kor upper body plyometrics, larger athletes (weight greater than 115 kg or 250 lbs.) should he able to bench press their body weight and athletes weighing less than 1 If) kg <250 lbs) should be able to bench press 1.5 times their body weight.
Plyometric training should never be undertaken if you have any leg, hip, arm, or shoulder injury.
Safety in Plyometric Training
Several steps can be taken to ensure that plyometrics training is site These measures include using an appropriate surface, footwear, and equipment, and proper technique.
Surface
Plyometrics should not be performed on hard surfaces such as concrete or steel, nor should they be performed on soft surfaces such as sand.
The best surface is a grass field, followed by artificial turf or wrestling mats.
Footwear
Recommended shoes are those that provide ankle and arch support, lateral stability, and have a wide, non-slip sole.
Equipment
Boxes that are used for in-depth or box jumps should have a non-slip top and should never exceed a height of 1.2 m (0.5 – 0.75 m is recommended: 1.5 to 2.5 ft. and less than 4 ft).
Medicine balls are commonly used for many of the exercises. This is a ball that weighs no more than 10% of your typical training weight. For example, if you regularly train with a 200 pound bench press, then the medicine ball you use should be no more than 20 lbs. These balls can be covered with leather, plastic, rubber, or any type of fabric.
Technique
As with other exercises, attention should be paid to proper technique. For example, when performing lunges, the knee angle should not exceed 90°. Any movement beyond this angle will place undue stress on knee cartilage and ligaments. Keeping the knee directly over and in line with the big toe will help maintain technique. The step should be straight out, not to the side. The shoulders should always be over the knees during landing when performing in-depth jumps.
Fatigue from high-volume training can compromise technique and result in injury. When technique begins to fail, it is time to stop the exercise and rest.
Program Design and the Overload Principle
Plyometrics training should be tailored to account for individual characteristics and the activity for which one is training. More stress will he placed on the muscles, joints, and connective tissue of heavier individuals, therefore, bigger operators (weight greater than 90 kg or 198 lbs.) should not perform high-intensity plyometric exercises.
Persons with a previous history of injury should be cleared by a medical officer prior to plyometric training.
A plyometrics program for the special operations community should incorporate those types of movements (i.e., linear, vertical, lateral, or a combination) required for operational performance. For example, downhill skiing would require diagonal movements, close-quarters battle (CQB) would require horizontal, vertical, and diagonal movements.
The overload principal is the basis for any training program whether it be cardiovascular training or the development of muscular strength, endurance, or power. The three basic variables used in the overload principal include the frequency, volume (or duration), and intensity of training. By increasing any one or a combination of these variables within a training program, one can continuously and safely overload the system that is to be trained (i.e., cardiovascular, muscular, neuromuscular).
Frequency
Frequency is the number of workouts per week (or other unit of time). For plyometric training, the range is usually from one to three sessions per week, depending on the sport and season. A plyometric training program for the Naval Special Warfare community should consist of two training sessions per week when operational demands require such training. Allow 2-3 days for recovery between workouts to avoid overtraining or injury.
Volume or Duration
The volume for plyometric training is defined as the number of foot contacts or landings per session.
♦ Beginners: 80-100 landings per session
♦ Intermediate: 100-120 landings per session
♦ Advanced: 120-140 landings per session
Intensity
The intensity for plyometrics training is the level of stress placed on the neuromuscular system, the connective tissue, and the joints, and is determined by the type of exercises performed. For example, skipping is a low intensity exercise while in-depth box jumps are of higher intensity. Some guidelines arc provided as follows:
♦ Vertical jumps are more stressful than horizontal jumps.
♦ One leg landings arc more stressful than landings on two feet.
Plyometric Training
Plyometric training should begin with a general warm-up followed by dynamic stretching (see Chapter 7 for stretching). Stretches should mimic the activity to be performed (e.g., 4-Way Lunges and Leg Swings for lower body plyometrics; Up Back and Overs or Press-Prcss-Fling for upper body plyometrics). Static stretches can also be added.
Two sessions of plyometrics per week are sufficient.
Heavy strength and plyometric training on the same body area should not be performed on the same day.
However, upper body strength training may he combined with lower body plyometrics and vice versa. Adequate time for recovery from each type of training is needed and can take from 1-3 days, depending on the intensity. If schedules are tight, the intensity of strength and plyometric exercises should vary from low to high to allow sufficient time for recovery. For instance, when high-intensity plyometrics is required strength training should be of a lower intensity.
Plyometric Exercises
When performing jumps it often helps to think of “hanging in the air” for as long as possible, keeping shoulders parallel to the ground at all times. Emphasis should be on speed without sacrificing proper technique.
