Saturday, June 30, 2012

Applied Plyometrics: Insights From Below the Iceberg's Tip



Applied plyometrics 

SHAWN MYSKA, CSCS*D, SPS,  Co-Founder and Athletic Director for Explosive 
Edge Athletics tells us how to reach high when "there's no limit but the sky."
*Coaches, trainers, and athletes have always sought out methods to increase explosive power, rate of force development, and reactive ability.  
Every practitioner has heard the promises of plyometric training to provide the link between strength in the weight room and speed on the field. 

In fact, the use of plyometrics has run rampant through American weight rooms since its introduction into the United States by Wilt in the mid 1970’s (3).    

Although plyometrics has been around for decades, many coaches and trainers still remain misinformed on how to properly incorporate plyometrics into their athlete and client training plans.


A few problematic and confusing issues that exist when it comes to the understanding and application of plyometrics include, but are not limited to:
  • in literature, there remains a lack of clear and concise terminology used when it comes to key theories
  • during training application, science is often overlooked at the expense of added intensity  
  • an abundance of misinformation exists regarding the scientific keys to plyometrics  

By definition, the word plyometrics literally means to ‘increase measurement’. However, the term plyometrics was originally intended to mean ‘eccentric contraction’. 

A more practical definition is a quick and powerful concentric movement, preceded by an active prestretch, or countermovement, that involves the use of the stretch-shortening cycle (SSC). 

MODELS: MECHANICAL VS NEURO PHYSIOLOGICAL

 

Two models exist to help explain the increased concentric power production seen during the SSC: the mechanical and the neurophysiological model. The mechanical model involves utilizing the elastic nature of the musculotendinous components, namely the series elastic component (SEC), to facilitate an increase in concentric muscle action. The neurophysiological model involves the potentiation of the concentric muscle action by use of the body’s natural stretch reflex. Both then combine, through an impulsive three phase cycle, to facilitate a maximal increase in force over a minimal amount of time. These three phases include the eccentric/yielding phase, the amortization or transition phase, and the concentric/overcoming phase.


That being said, one thing about the SSC has been clear from early research and remains true today; the amortization or transition phase of the SSC appears to be the most crucial in allowing for greater power production in the concentric phase of plyometric movements (1, 2). 

The amortization time and coupling time (in relation to an individual’s reactive ability) can be looked at as the time from the end of the eccentric phase to the initiation of the concentric muscle action. During this phase, several physiological events take place that will determine the duration of the phase. 

In any event, the time delay must be kept short in duration because if a concentric muscle action does not occur immediately following the eccentric phase, the stored energy from the SEC and the potentiating ability of the stretch reflex will be negated.  In addition, two other parameters on the eccentric/yielding portion of the SSC are found to be important to the restitution of elastic energy and the potentiation effect; if there is  
  1. Too large of range of motion/distance at a joint or if
  2.  The eccentric phase takes too long; the stored energy dissipates and is expired as heat.

TRAINING: BEST PRACTICES

 

So what can we do as coaches and trainers to focus on these scientific keys during the training of SSC exercises? 

As mentioned above, because the amortization and transition time is arguably the most important phase of the SSC, proper and efficient landings become paramount.  Thus, pre-landing body position as well as maintaining posture, balance, and stability after ground contact is key (2).  An athlete should learn to land on the balls of the feet (front two-thirds of the foot) with the ankle dorsiflexed and with slight flexion at all major joints involved upon landing. If the heels touch the ground during the contact phase, the intensity or load to overcome is too great and should be reduced (1, 2). The shoulders, knees, and toes should all be in alignment in this landing position. All of these biomechanical considerations in combination will allow for the quickest absorption rate, lowest ground contact time, and a more rapid recovery of potential energy which will make a more powerful concentric action more likely.

Without having proper landing mechanisms, it is unlikely that we can expect an athlete to be able to efficiently stabilize the forces at the time of ground contact and switch into a positive work position in the amortization time window.  In addition, because of the extreme amounts of forces the body is required to withstand in many plyometric exercises, having incorrect landing mechanisms could put our athletes at a much greater risk of technical inefficiency or so-called non-contact injury. Basically, the quicker an athlete is able to switch from yielding (eccentric) work to overcoming (concentric) work the safer the movement becomes (2).
The amount of this coupling time (which is also referred to as amortization in this article) will make the difference as to how the SSC of that movement is classified. In order to be of true plyometric nature and take advantage of the SSC, amortization times should be of 250ms or less. In addition, famed Sports Scientist Marteen Bobbert has suggested different landing techniques in order to not only keep amortization times low but also to have specific carryover to sport. 

A good guideline based on his research suggests that an athlete should execute most jumping movements (plyometrics) in a ‘bounce’/undampened fashion where an athlete aims to land and immediately complete the push-off/take-off phase with little counter movement and ground contact time. (1, 2).


Obviously, I have only briefly addressed some plyometric subjects that we could go into much more detail with. However, if this very loaded topic interests you, I will be shedding even greater light on all of the factors, components, and underlying mechanisms that it entails at the FEI Eclipse event coming up later this month. 


I hope to see y’all in New York City on June 30th!
No Limits But The Sky!
______________________________________________________________________
1. Bobbert, Maarten F. Drop Jumping as a Training Method for Jumping Ability. Sports Medicine, 9 (1): 7-22, 1990.
2. Radcliffe, James C, and Farentinos, Robert C. High Powered Plyometrics. Champaign, IL: Human Kinetics, 1999.
3. Wilt, F. Plyometrics-What it is and how it works. Athletic Journal, 55: 76, 89-90, 1975.

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