What type of muscle contraction occurs between landing and jumping during plyometric training?

Lately, it seems like the hottest thing in training is the incorporation of plyometrics within programming. On almost a daily basis you can get on your social media account and see a video of someone jumping onto, or over something. However, do any of these people know why they are performing these jumps or the advantages to a properly designed plyometric program?

First, you must understand what constitutes a true plyometric action. Fred Wilt, who introduced the United States to plyometric training, refers to plyometrics as the following, “the exercises or training drills used in producing an overload of isometric type muscle action which invokes the stretch reflex of muscles”. The term is defined by Webster as, “Exercise involving repeated rapid stretching and contracting of muscles to increase muscle power”. I know this probably makes the concept clear as mud at this point, especially for non-kinesiology/exercise science majors so let me explain further.

First, let’s break down the mechanics of any plyometric movement. The muscle has three types of contractions: eccentric, isometric, concentric. An eccentric contract occurs when the muscle is working as it is becoming longer. Picture a heavy weight in the bed of a pick up truck. To take that weight out of the truck bed and place it on the ground I have to reach in and pick up the object with my elbows at 90 degrees. Then to lower it to the ground I have to straighten my elbows at some point. Well this action of slowly straightening my elbows to lower the object is an eccentric contraction. Now, if I pick up that weight from the bed of the truck and carry it for a certain distance with my elbows maintaining that 90 degree angle this is an isometric contraction, because my muscle is activated and working but the muscle is not becoming any shorter or longer. Finally, if I pick up that object and want to lift it higher I have to do so by bending my elbows even greater than 90 degrees. This is a concentric contraction, because my muscle is shortening as it working in order to lift the weight higher.

So now that you understand the three types of muscle actions, we can talk about how they are involved in a plyometric movement. In the definition above from Fred Wilt, he references the stretch reflex. You will also hear the term Stretch Shortening Cycle when talking about plyometrics. This physiological adaptation refers to a movement produced by a structure within the muscle known as the Muscle
Spindle. When the muscle is placed under a rapid stretch the muscle spindle sends a signal to the spine which then signals the muscle to contract and shorten in order to prevent the muscle from over stretching. The Stretch Shortening Cycle is key to plyometric training. If you think about someone jumping rope and visualize the ankle during the movement you are visualizing a plyometric exercise. As the person’s body comes down there is a stretch occurring within the calf muscle and Achilles tendon. This is the eccentric contraction of movement. The calf is contracting while it is being lengthened in order to slow the body down to a stopped position in order to reaccelerate it back in an upward motion. When the body stops the fall and before it moves back upward it is stopped for a brief second. This is an isometric contraction or otherwise known as the amortization phase of a plyometric. Finally, the body is propelled back upward which is the concentric contraction of the calf.

It is important during any training program to stimulate each of these phases of a plyometric. However, many times you see the concentric phase being overloaded and exploited, i.e. every extreme box jump video you have ever seen on Youtube. I am not discrediting the importance of being concentrically powerful, however, there is more to being powerful than just jumping high. In the remainder of this article I want to discuss the importance of eccentric loading in regards to plyometrics.

When it comes to teaching plyometric progressions I always start all of my athletes with eccentrics, regardless of age. If the body does not know how to decelerate from a movement then we do not need to be instructing it on how to accelerate faster. That is like increasing the horsepower on a car that has no breaks. That ride will be fun, but only for a short period of time. The ability to load properly is also crucial for all of sport. First, from an injury prevention standpoint the athlete must be able to land from a jump or slowdown from any speed in order to move in another direction without compromising the body’s position. Secondly, from a performance standpoint, the more efficiently the body accepts forces the faster it will be able to change directions.

The simplest eccentric that all of my athletes will learn within the first session is a drop. This simply means the athlete will go from a tall standing position and quickly drop into an athletic position. I am looking for the knee to be over the ankle, the weight to be evenly distributed between the fore foot and hind foot, and for the back to be flat with good posture. From hear the athletes will learn to drop from higher positions causing them to fall at a greater velocity before hitting the ground. 

Now, learning how to eccentrically load is not limited to dropping straight down. Athletes must also be able to load against an anterior force, posterior force, lateral force, as well as any combination of these forces. This is not something I will cover in my first session, however, it will be covered within the first few weeks. It is also important to test these abilities unilaterally. Sport is chaotic. It is nearly impossible for me to try to simulate every type of game-time situation. However, I must try to prepare each of my athletes for as many different situations as I can. There will be times that an athlete on has one leg available to land on due to an awkward position in basketball or they may have to cut with the leg that they are uncomfortable using when making a move on the football field. These are the situations that require the athlete to be prepared to accept and reapply forces.

As you can see from the examples above, simply performing countless box jumps will not prepare you for the demands of sport. There should be a well-thought out plan of bi-lateral and uni-lateral movements, eccentrics and concentrics, jumps, hops, bounds, and combinations of each. 

One of the fathers of Plyometric Training is Dr. Yuri Verkhoshansky. Dr. Verkhoshansky explains in his book Special Strength Training that athletes don’t necessarily need to be stronger to be more powerful. Many athletes can improve their power by learning to synchronize their muscular activation. One way to go about training this synchronization is through plyometric training. However, before you try to jump on a shaky stack of boxes at the gym, try landing from that height first. 

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