Exercise Science Review 1-6, Intro to Plyometrics

Posted by on Jan 23, 2013 in Exercise Science, Review Topics | 0 comments

Plyometrics is defined as a quick, powerful movement that begins with a counter movement, or “pre-stretch”.

Imagine you are about to take a jump, instinctively you bend at the hips and knees before exploding with violent hip and knee extension propelling yourself into the air.  The initial bend at the hips and knees is the “pre-stretch” and it stores energy in your muscle fibers and connective tissue and releases it upon contraction.  This is known as the Stretch Shortening Cycle, and as you can tell from the wikipedia article some of the science around exactly why this works is difficult to nail down.

Nevertheless, the bottom line is dynamically pre-stretching a muscle increases output power.  Whether this is by increased innervation from the CNS or stored energy in the elastic tissue, or some of both, the goal here is to know some of the theory and practical applications.

Muscle Mechanical Diagram

Muscle Mechanical Diagram

Above is a mechanical diagram that is often used to represent the components involved in the stretch shortening cycle.

Parallel Elastic Component (PEC)

The PEC or Parallel Elastic Component, is comprised of the epimysium, perimysium, endomysium, and sarcolemme.  It exerts a passive force when the muscles are being stretched but not activated.

Series Elastic Component (SEC)

The Series Elastic Component stores the majority of the energy in the plyometric exercise.  The SEC is comprised mostly of tendons, and they act like a spring.  As energy is stored during the stretch phase, the tendons lengthen and store elastic energy.  Following the eccentric phase, the energy is released if immediately followed by a concentric phase.  Otherwise the stored energy is lost as heat.

Contractile Component (CC)

The contractile component is exactly what it sounds like, the component of the muscle doing what we always expect muscles to do: contract.  Composed of actin, myosin, and cross-bridges as covered in chapter 4 of the book.  If you don’t know what those last words meant, start here on wikipedia: Actin, Myosin…though the wikipedia articles probably go into more detail than you need for the CSCS Exam.

There is more on plyometrics you will need to know for the CSCS Exam, specifically the three phases of the stretch shortening cycle as well as program design for plyometrics.  I will get into these topics later, but won’t be covering them in my first review series.

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