Editing Plyometrics (section)

==Method==
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.<ref>{{cite journal|author1=A.S. Medvedev |author2=V.V. Marchenko |author3=S.V. Fomichenko |title=Speed-Strength Structure of Vertical Jumps by Qualified Weightlifters in Different Take-off Conditions (Condensed)|journal=Soviet Sports Review International-Teoriya I Praktika Fizicheskoi Kultury|volume=19|pages=164–167|year=1983}}</ref>  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 {{convert|20|-|30|in|cm}} 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.<ref name="Verkhoshanski2" />

More specifically, the muscles and tendons undergo a stretch (eccentric contraction) while landing which is needed to absorb some of the force generated but most importantly, to withstand the force that is produced by the shock that occurs on the landing. The greater the shock (forces experienced on landing), the stronger the eccentric contraction will be, which in turn produces even greater tension.  This tension, which is potential force, is then given back in the return movement when the muscular contractions switch to the concentric or shortening regime.<ref name="Yessis" />

However, for maximum return of energy, minimum time must elapse from when the force is received to when they are returned. The greater the time between receiving the forces and giving them back, the less is the return and the less the height that can be achieved in the jump.  Most of the lengthening and shortening occurs in the respective muscle tendons which have greater elasticity.

Another way of saying this is that the faster the switching from the eccentric to the concentric contraction, the greater will be the force produced and the greater the return movement.  The speed of the switching is extremely fast, 0.20 seconds or less.  For example, high-level sprinters execute the switch from the eccentric contraction that occurs when the foot hits the ground to the concentric contraction when the foot breaks contact with the ground in less than 0.10 seconds.  In world-class sprinters, the time is approximately 0.08 seconds.
The exact platform height used by most athletes in the depth jump should be less than {{convert|30|in|cm}} in the early stages of training.  Most athletes start at approximately {{convert|12|in|cm}} after doing some jump training. They then gradually work up to {{convert|20|in|cm}} and then to 30 inches depending upon how well the jumps are executed. The main criterion is that the athlete is jumping as high as possible on every jump.

If the athlete gradually improves his jump height, the same platform height is continued until increases in jump height are no longer observed. At this time, takeoff height is increased by a few inches. If the athlete continually fails to jump very high, the height of the drop-down is lowered somewhat.<ref>{{cite journal|author1=N.I. Volkov |author2=V.M. Koryagin |title=Systematization of Special Basketball Exercises (Condensed)|journal=Yessis Review of Soviet Physical Education and Sports|volume=13 #4|pages=110–111|year=1976}}</ref>  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 {{convert|40|in|cm}}.  Rather than developing greater explosive power this height leads to more eccentric strength development.  Going higher than {{convert|30|in|cm}} 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.<ref>{{cite journal|author1=N.A. Masalgin |author2=Y.V. Verkhoshansky |author3=L.L. Golovina |author4=A.M. Naraliev |title=The Influence of the Shock Method of Training on the Electromyographic Parameters of Explosive Effort|journal=Teoriya I Praktika Fizicheskoi Kultury (Theory and Practice of Physical Culture)|volume=1|pages=45–46|year=1987}}</ref> 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.<ref name="Dr. Yuri Verkhoshansky, Natalia Verkhoshansky 2011">{{cite book |author1=Yuri Verkhoshansky |author2=Natalia Verkhoshansky |title=Specialized Strength and Conditioning, Manual For Coaches|publisher=Verkhoshansky SSTM|year=2011}}</ref>  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.<ref name="Dr. Yuri Verkhoshansky, Natalia Verkhoshansky 2011"/>

Technique of jumping is also very important when executing plyometric exercises. In essence, the athlete goes into a slight squat (crouch) upon landing in which the hip, knee, and ankle joints flex.  The takeoff or jump upward is executed in a sequence initiated by hip-joint extension followed by knee-joint extension which begins during the hip-joint extension.  As the knee-joint extension is taking place, ankle-joint extension begins and is the only action that occurs as the takeoff (breaking contact with the ground) takes place.  All three actions contribute force to the upward jump, but the knee-joint extension is the major contributor.<ref name="Yessis2000" />