Максимальная взрывная сила: плиометрические упражнения.

Maximum intensity explosive exercises

Plyometrics, also known as jump training or plyos, are exercises in which muscles exert maximum force in short intervals of time, with the goal of increasing power (speed strength). This training focuses on learning to move from a muscle extension to a contraction in a rapid or "explosive" manner, such as in specialized repeated jumping. Plyometrics are primarily used by athletes, especially martial artists, sprinters and high jumpers, to improve performance, and are used in the fitness field to a much lesser degree.

Plyometrics include explosive exercises to activate the quick response and elastic properties of the major muscles. It was initially adopted by Soviet Olympians in the 1950s, and then by sportspeople worldwide. Sports using plyometrics include basketball, tennis, badminton, squash and volleyball as well as the various codes of football. The term "plyometrics" was coined by Fred Wilt after watching Soviet athletes prepare for their events in track and field. He began a collaboration with trainer Michael Yessis to promote plyometrics. Since its introduction in the early 1980s, two forms of plyometrics have evolved. In the original version, created by Russian scientist Yuri Verkhoshansky, it was defined as the shock method. In this, the athlete would drop down from a height and experience a "shock" upon landing. This in turn would bring about a forced eccentric contraction which was then immediately switched to a concentric contraction as the athlete jumped upward. The landing and takeoff were executed in an extremely short period of time, in the range of 0.1–0.2 second. Several imaginary Greek words that would explain the y have been cited.

In the depth jump, the athlete experiences a shock on landing in which the hip, knee, and ankle extensor muscles undergo a powerful eccentric contraction. For the muscles to respond explosively, the eccentric contraction is then quickly switched to the isometric (when the downward movement stops) and then the concentric contraction, in a minimum amount of time. This allows the athlete to jump upward as high as possible. In the eccentric contraction, the muscles are involuntarily lengthened, while in the concentric contraction, the muscles are shortened after being tensed. Most of the stretching and shortening takes place in the tendons that attach to the muscles involved rather than in the muscles. To execute the depth jump, the athlete stands on a raised platform, usually not greater than high, and then steps out and drops down in a vertical pathway to make contact with the floor. The height used by most athletes is usually quite low in the early stages of training. The key is how high the athlete jumps in relation to the height of the takeoff platform. Technique and jump height are most important at this time. While the body is dropping, the athlete consciously prepares the muscles for the impact by tensing the muscles. The flooring upon which the athlete drops down on should be somewhat resilient, mainly for prevention of injury. Upon making contact with the floor, the athlete then goes into slight leg flex to absorb some of the force for safety. However, the main role played by the muscles and tendons is to withstand the force that is experienced in the landing. This force is withstood in eccentric contraction. When muscle contraction is sufficiently great, it is able to stop the downward movement very quickly. This phase is sometimes called the phase of amortization in which the athlete absorbs some of the force and stops downward movement by the strong eccentric contraction of the muscles. The strong eccentric contraction prepares the muscles to switch to the concentric contraction in an explosive manner for takeoff. When the athlete drops down to the floor, the body experiences an impact upon landing. The higher the height of the step off platform, the greater the impact force upon landing. This creates a shock to the body which the body responds to by undergoing a strong involuntary muscular contraction to prevent the body from collapsing on the ground. This in turn produces great tension in the muscles and tendons which is then given back in a return upward movement. The faster the change in the muscular contractions, the greater the power created and the resulting height attained. Most important here is how high the athlete jumps after the drop down. The maximum platform height used by a high level athlete is no more than Rather than developing greater explosive power this height leads to more eccentric strength development. Going higher than is usually counterproductive and may lead to injury. This occurs when the intensity of the forced involuntary eccentric contraction upon landing is greater than the muscles can withstand. In addition, the athlete will not be able to execute a quick return (fast transition between muscular contractions), which is the key to successful execution of explosive plyometrics. Because of the forces involved and the quickness of execution, the central nervous system is strongly involved. It is important that the athlete not overdo using the shock plyometric method. Doing so will lead to great fatigue, and, according to Verkhoshansky, sleep disturbances. Athletes have great difficulty sleeping well if they execute too many depth jumps. This indicates that athletes must be well prepared physically before doing this type of training.

Many professional and Olympic athletes use plyometrics training to improve muscular strength and jumping abilities which therefore increases their power. There are varying levels of intensity to plyometrics. Another benefit of plyometrics is that you can vary your level of intensity which means anyone looking to improve strength and jumping training can be involved regardless of fitness. With there being so many exercises this means you are less likely to get burned out and have a wide range of exercises to choose from. Another good reason with so many exercises being available are that you can find exercises that don't require the use of any equipment. It also increases muscular strength and endurance, also increases metabolic rate which increases weight loss and heart rate.

Plyometric exercises are sometimes performed with an additional load, or weight added. In such cases, they are referred to as loaded plyometrics or weighted jumps. The weight is held or worn. It may be in the form of a barbell, trap bar, dumbbells, or weighted vest. For instance, a vertical jump whilst holding a trap bar or jumping split squats whilst holding dumbbells. In addition, a regular weight lifting exercise is sometimes given a plyometric component, such as is found in a loaded jump squat. Jumping onto plyo boxes or over hurdles whilst holding weights is not recommended for safety reasons. The advantage of loaded plyometric exercises is that they increase the overall force with which the exercise is performed. This can enhance the positive effect of the exercise and further increase the practitioner's ability to apply explosive power.

Unilateral plyometrics are jumping exercises which involve only one foot being in contact with the ground at some stage. This can include jumping off of, and landing on, the same foot i. e. hopping, jumping from one foot and then landing on the other, jumping from one foot and landing on two, or jumping off two and landing on one. It typically makes more intense demands on the legs than bilateral plyometric training and can be used to further enhance explosive power. The intensity of the exercises can be manipulated through the adjusting of box and hurdle height, and any weight which is held or worn. The greatest intensity can be achieved whereby the height or the distance travelled is maximised. A hop test involves a comparison between the hopping height or distance achievable by the left and right legs, considered separately. It is used to assess the relative strength levels of each leg and whether there is a muscle imbalance i. e. a strength discrepancy between the left and right sides which results in a significant variation in the results. If such an imbalance is found, unilateral plyometrics may be used to alleviate it. As the legs are used singly, and perform the same amount of work, the body and legs may be strengthened more evenly than bilateral plyometrics, which may involve one leg doing an excessively large amount of the work. Some forms of unilateral plyometrics involve a cyclic alternation between the legs e. g. repeatedly jumping from one foot to the other. As runners perform a similar action of alternating between left and right legs, and each step has an acceleration phase like a jump does, then based upon this commonality, such unilateral plyometrics are considered to transfer effectively to running and sprinting and improve performance.