‘Plyometric’ is probably the most abused training term in existence. Colloquially it seems to be employed to encompass any power exercise, regardless of how it’s performed. This article will recap what Plyo’s actually are and how they work.
What is the SSC?
The stretch shortening cycle (SSC) defines plyometric exercise. It is the sequential occurrence of 3 distinct phases of action through the muscle-tendon unit (MTU):
- The eccentric (pre-stretch) phase
- The transition (amortisation) phase
- The concentric (contraction) phase
What is a true ‘Plyometric’ exercise?
‘Plyo’ is thought to derive from the Greek work ‘pleythyein’ meaning to augment or increase. Plyometric exercise seeks to augment power output through by utilising properties of the SSC – the properties predict that a muscle should produce greater force in the concentric phase of the SSC when immediately preceded by a rapid eccentric action.
Why should they work?
There are both mechanical and neural models which may contribute to the enhancement of power associated with Plyo’s. General consensus (i.e. the NSCA ‘Essentials’ book!) focuses on:
- Increased utilisation of elastic energy – the idea that the MTU acts in a spring-like manner
- Contribution of the stretch reflex – the idea that a rapid stretch of a muscle primes a more powerful reversal of force as an in-built protective mechanism
However, several additional mechanisms may also contribute to the Plyo phenomenon. For example, increases in active range of movement, time available for force production and pre-tension. The contributory mechanisms to plyometric induced augmentation shouldn’t be seen as independent of one another, they work synergistically. The important part is understanding how we may exploit these mechanisms to improve performance.
What is the key to Plyo’s?
What these key contributory mechanisms have in common is that their dependence on the following:
- A rapid eccentric (pre-stretch) phase
- A short transition (amortisation) phase
This is where Plyo’s get butchered. As these phases become longer in duration the potential for performance augmentation dwindles until it eventually becomes non-existent. And we’re not talking in seconds here either, we’re talking tenths and hundredths of a second! Nine times out of ten, the emphasis during plyometrics should be on minimising the transition phase and being ‘quick off the floor’.
What limits Plyo performance?
Now it’s very well saying that we want an athlete to be quick off the floor, but with the best will in the world it may not always be possible. Why? Because this speed off the floor is reliant on the leg acting like a stiff spring. To act like a stiff spring the muscles in the leg need to be pre-activated – or ‘switched on’ – at the transition phase. The problem is that the body’s natural reaction is to inhibit – or ‘switch off’ – muscles and reduce this stiffness. Again, it’s an in-built mechanism to try and protect against injury. The body needs to be coaxed into reducing this inhibition and allowing itself to effectively absorb and then reapply force.
You can’t start introduce yourself to plyometric training by jumping off a 50cm box. Plyo’s need to be introduced slowly and progressively in order to be safe and effective.
Is strength important?
Do you even have to ask this question! The body needs to be strong in order to absorb and apply force effectively regardless of the context. Always remember the priorities of power development:
- When weak, get strong
- When strong, get fast
You don’t need to take any notice of the whole NSCA rulebook about being about to squat 1.5x your bodyweight before being allowed to jump, but remember that getting strong is the first priority!
What can Plyo’s improve?
Plyometrics, done well, will improve an individual’s ability to utilise the SSC. Improving SSC ability would intuitively have two benefits: the augmentation of maximal power and/or the conservation of muscle energy at a given workload. With this in mind, research demonstrates that plyometric training can improve:
- Jump performance (Sáez de Villarreal, 2009 – meta analysis)
- Injury incidence (Hewett et al, 2006 – meta analysis)
- Sprint performance (Sáez de Villarreal, 2012 – meta analysis)
- Strength (Sáez de Villarreal, 2010 – meta analysis)
- Muscle co-activation (e.g. Chimera et al, 2004)
- Force absorption (e.g. Irmischer et al, 2002; Vescovi et al, 2008)
- Running economy (e.g. Spurrs et al, 2003; Berryman et al, 2010)
- Kicking distance (e.g. Rubley et al, 2009)
Not an exhaustive list, but a good indication of how widespread the potential benefits of plyometrics are.
Understanding the principles of plyometric training is crucial if you’re planning to employ them as an effective training modality. As for specifics regarding the prescription and coaching of plyometrics, I guess that’s a topic for another day…