Monday, December 6, 2010

Plyometrics, more than jumping onto a box Part 2

Part one we discussed that basic mechanics of what is shown during a SSC. Now in Part II we will look at the optimal ways in which you can train this quality.

What does this say about training reactivity and explosiveness?

The impact of external forces upon ground contact causes a rapid lengthening leading to a stretch reflex. If the muscle is increasing in stiffness (acting isometrically, contracting) but you are still gaining range of motion, then the tendon is what is lengthening. The external forces that cause the body to produce force in this way come in several forms. These all require short ground contact and pretension (muscle rigidity). When the body drops before foot placement, the anticipatory reaction pretenses the muscles witch puts the SEC at somewhat of a pre-stretch. Indicating that drills to develop this capacity should be following a brief landing. Drills that fall in this category:

Double contact jumps: Perform 1 or 2 quick taps with both feet before performing jump.

Continuous jumps/bounds: performing a sequence of jumps with as little ground contact time as possible.

Depth Jumps: Performing a jump from an elevated box with as little ground contact as possible. Box height should never exceed jump height.

What about the good ole’ vertical jump (countermovement)?

In this case, the impact of external forces occurs slowly. This allows the muscle to act eccentrically not allowing the tendon to lengthen as much. This jump would have little to do with reactive explosiveness. In many sports, the case is getting into the air from a running start or rebounding back into the air following a jump, utilizing the methods discussed previously. In many respects the countermovement jump isn’t nearly as “functional” when determining an athletes reactivity and explosiveness.

A Word About Strength
Readiness to perform this type of plyometric work requires a pre-requisite of strength development. In order to get the most stretch out of the tendon the muscle must be strong enough to hold itself isometrically. On a more serious note, if you perform depth jumps and the force greatly exceeds the muscles isometric ability, you will end up with a tear. Again it all comes down to readiness and how advanced you are in your training. A good way to tell if you should progress to the next level is whether the athlete can maintain relatively small hip and knee angles upon landing or rebounding (more upright).

Benefits of progression

This isn’t to say that the countermovement or static jump should be thrown out. These do a great service to build coordination and landing mechanics. An adaptation that reduces co-contraction of the antagonist also occurs. Finally, a static jump is a great companion to starting strength.

Final Note

I hope what you get out of this information is the need to expand across several methods or ways of developing reactivity and explosiveness. By keeping to one method or worse, not doing any plyometrics at all, you are stripping the athlete’s ability to perform at the highest level. Progress, be smart, and stay healthy.

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