So firstly, what is plyometric training?
Plyometric training is a combination of sheer strength combined with the intention to move as quickly as possible. But that is not all. Pure plyometric training also requires that the muscles being worked are pre-loaded during the eccentric (downward) phase, immediately prior to their forceful concentric (upward) contraction. This pre-loading causes what is known as the ‘Stretch-reflex’ or ‘Stretch Shortening Cycle’ - SSC to occur. This is a neurological mechanism that adds more force to a muscle contraction than if it was contracted without the pre-load.
It works like this…
The ECCENTRIC phase of a movement quickly lengthens the muscles controlling the moving (flexing) joints – loading them up with a high force which, along with the rapid rate of lengthening, is detected by the muscle spindles (proprioceptors, that feed back to the Central Nervous System). The greater the loading in the eccentric phase, the greater the SSC contribution to the following muscle contraction (up to a point – it is of course possible to overload the eccentric phase causing us to crumple into the ground!).
The AMORTISATION phase is the point at which when the lengthened muscles dynamically stabilise the joint and prepare for the next phase. It is the point at which there is a momentary pause in movement. This phase should be kept as short as possible.
Finally, the CONCENTRIC contraction of the muscles causes the explosive extension of the joints and thus body movement to occur.
As an example…
In a bounding jump, to jump as far/high as possible, the following movement pattern should occur:
The jumper takes off and then lands and begins to crouch down (hip, knee and ankle flexion) by eccentrically lengthening his/her leg muscles. This not only absorbs the landing forces but if done correctly, pre-loads the muscles and causes the SSC to kick in.
The jumper reaches the depth of their crouch and then very quickly stabilises their joints during a momentary pause (amortisation phase) ready for…
The concentric, explosive extension of the legs in order to jump as far/high as possible
Tips to do plyometrics well…
Firstly, think about the joint angle at which we can optimally move quickly and with force. This angle should be a relatively open angle ie, the joint should be roughly 2/3s through its extension – not quite fully extended (or the muscle lengthened to approximately 1.2 times it’s resting length). Of course, we are not all the same, but generally, with practice, people will find the correct joint angles for themselves given their own individual strength, lever length, bodyweight etc.
Secondly, we should minimise the amortisation duration to as short a time as possible. This means that you should focus on transferring from eccentric to concentric muscle actions as quickly as possible. Total contact time with the floor should optimally be less than 0.2 seconds.
Thirdly, we should complete the exercise with maximal intention to move as fast as possible. This is a supra-maximal effort, in that the forces being produced should be greater than those concentrically produced without the pre-load. Don’t train to fatigue – finish your session buzzing and as though you could still do a bit more.
Plyometrics is good for…
Anyone with a reasonable background and training history in strength training. Note, it is not advisable for those with injuries, those who are overweight or those with porr movement control.
It’s uses include…
Greater rate of force production (acceleration)
Greater running economy
Increased running velocity
Increased change of direction quickness
Increased jump height/length
Transfer of neurological gains to other exercise modalities including strength and power weightlifting
Plyometric Training is part of the new Level 2 Certificate in the Foundations of Strength and Conditioning (Trainer) - available soon!