Prescribing Plyometrics

Plyometrics are tried and true throughout many years of sports performance training. Developing the stretch shortening cycle is vital for maximizing performance. An efficient stretch shortening cycle allows for more force to be produced in shorter time frames at a lower energy cost. An efficient stretch shortening cycle comes from a fast transition from the eccentric to concentric action. It is all about harnessing elastic energy. During an eccentric action, the tendon lengthens, storing elastic energy. The faster an athlete can go through the stretch shortening cycle, the greater the elastic energy return, and lesser metabolic expenditure. Every time an athlete makes contact with the ground, whether through jogging, sprinting, cutting, jumping they are experiencing a plyometric action. Therefore, negating the metabolic cost of these ground contacts by developing an efficient, robust stretch shortening cycle is vital.

There are countless plyometric variations, and countless ways to classify them. There is no singular methodology for this, but it is important to have your own organization method for them so you can have a direction for how you want to prescribe and progress plyometrics for your athletes. I categorize them as: 1. Explosive Strength 2. Elastic Strength then break them down into: direction, quality, variation and intensity.

Quality	Direction	Intensity
Explosive Strength	Vertical	Extensive
Elastic Strength	Horizontal	Intensive
	Multidirectional	Shock

Explosive vs Elastic 

Explosive vs elastic strength can also be defined as slow stretch shortening cycle (SSC) and Fast SSC. Slow SSC variations display longer ground contact times(GCT) (<250ms) and deeper joint angles. Due to the longer ground contact times, performance is dependent on the contractile components of muscle. There is still an elastic component, but the longer GCT calls for greater levels of crossbridge formation from the myofilaments, and therefore greater concentric force production. Fast SSC plyos have quicker GCTs (<250ms) with less flexion of the joints. They are more dependent on storage of elastic energy in the series elastic component(SEC), compared to contractile components. Due to the faster movement duration, fast SSC plyos produce less force than slow SSC, but have a higher rate of force development (2).  Your leaner athletes who may not be strong in the weight room, but are fast and “bouncy” typically perform better in fast SSC variations. Athletes who are strong in the weight room typically respond better to slow SSC variations., due to the greater reliance on raw muscular power. 

Video 1: Fast SSC

Video 2: Slow SSC

As you can see in the videos above, I have a same athlete performing 2 different exercises. Both exercises train unilateral explosiveness, but the the way in which he expresses the explosiveness is much different between the two.

All forms of jumps and plyometrics improve rate of force development and power. However, different variations stress different methods of force production, yielding different adaptations. Depending on the time of the year and strengths/weaknesses of the athlete, it is important to prescribe plyometrics based off the desired adaptation. 

Slow SSC Adaptations

Due to increased stability, deeper flexion angles (and therefore tension on the muscle-tendon unit), longer GCTs, slow SSC jumps and plyos provide more of a strength stimulus. These activities require a sharp rise in concentric force production. They challenge how fast the brain can send an impulse to the muscle fibers. Due to the movement duration, they transfer to activities such as early acceleration (steps 1-3), standing vertical jump, changing direction at a deep angle, a lineman exploding off the ball. 

Fast SSC Adaptations

Fast SSC plyometrics have an increased demand for rhythm and coordination, as well as stiffness of the musculotendinous unit (MTU). They yield adaptations of smoothness and stiffness. I know that may sound contradicting, but hear me out. Power output of the upward phase of a plyometric depends how well the athlete stores elastic energy within the tendons during the lengthening phase. Proper release of elastic energy depends on the athlete's ability to quickly reverse the stretch placed on the MTU, requiring a fast GCT. Stiffness is resisting deformation. The stiffer a joint is upon impact with the ground, the quicker the GCT, and the higher the force production. The more compliant a joint is upon ground contact, the longer the GCT will be, the more energy will be dissipated, and the lower the subsequent force output will be (2). This optimization of elastic energy return involves proper timing of tension and relaxation and dynamic postural control. In order to maximize contraction dynamics in a plyometric action, muscles must turn on and off in a coordinated manner. Just prior to ground contact, there must be pretension in the agonist muscles in order to increase joint stiffness (1) and stretch the tendon. While the muscles shorten due to pretensing, the tendon lengthens, allowing for greater elastic energy storage. Following the eccentric action, there must be a fast relaxation of the antagonist muscles. This is known as “Sherrington’s Law of Reciprocal Inhibition”(cite). Take a pogo jump for example. The athlete gets off the ground by plantarflexing the ankle. In order for maximal contribution of the plantarflexor muscles of the ankle, the dorsiflexors must relax. Russian literature has shown the difference between elite and recreational athletes is not the rate at which muscles contract, but the rate at which they relax (3). This relationship is more pronounced at high velocities, pointing to the importance of timing in short GCT plyos. 

	Slow SSC	Fast SSC
GCT	>0.25s	<0.25s
Method of force application	Contractile component of muscles	Elastic energy storage in SEC
Variations	-Standing vertical jumps -Broad jumps -Depth Jumps  -Single/Double response multidirectional Jumps	-Hops -Bounds -Repeat hurdle jumps -Drop Jumps
Transfer	Early acceleration Standing vertical jump Deep cuts	Max velocity sprinting Triple jump Shallow cuts

Needs of the Athlete 

When determining which type to use, the sports performance coach must consider the sport/position demand and desired adaptation. Different sporting tasks require different explosive qualities. 

Tim Caron wrote about eccentric vs concentric athletes in his book The Strength Deficit. I believe this should be noted when prescribing plyometrics. Think of the difference in demands between a soccer player and an American football linemen. Linemen work in short spaces, requiring all-out explosive efforts. This requires a high concentric rate of force development. Therefore, explosive strength is an essential adaptation to chase. Soccer players work in large spaces, requiring cyclical efforts. The more space one is covering, the higher eccentric demand, the shorter the GCT, and therefore responsibility of the fast stretch shortening cycle. These athletes need to be able to store elastic energy within their tendons, and quickly get off the ground This is not to say soccer athletes can’t benefit from slow SSC plyos and linemen can’t benefit from Fast SSC plyos, but their sport demands point to where the focus of their training should be.

Individual strengths and weaknesses should also be noted when prescribing plyometrics. Some athletes respond better to fast SSC variations, while some respond better to slow SSC. Typically, leaner athletes perform better in fast SSC, while thicker athletes respond better to slow SSC. Joel Smith has put out good content on this, pointing at the differences in infrasternal angle(ISA). Narrow ISA athletes are the lean, bouncy athletes who may not have big weight room numbers, but their smoothness and elasticity suit them for fast SSC variations, while wide ISA athletes respond better to heavy lifting, and more muscular dominant slow SSC variations. 

A good rule of thumb is to address weaknesses in the offseason, then peak with strengths. For example, a narrow ISA athlete would perform slow SSC variations in the offseason, then focus on his strength of fast SSC, bouncy plyos as the season approaches. 

There are countless variations of plyometrics, and countless methods of progression. It is easy to get lost in all the information out there. There is not a singular right method, but it is important to understand the adaptation you are targeting, and the optimal prescription to apply to yield that adaptation. 

References

1. Comfort, P., Allen, M., & Graham-Smith, P. (2011). Comparisons of peak ground reaction force and rate of force development during variations of the Power Clean. Journal of Strength and Conditioning Research, 25(5), 1235–1239. https://doi.org/10.1519/jsc.0b013e3181d6dc0d 

2. Davies, G., Riemann, B. L., & Manske, R. (2015). CURRENT CONCEPTS OF PLYOMETRIC EXERCISE. International journal of sports physical therapy, 10(6), 760–786.

3. Siff MC (2003) Supertraining. Denver, CO: Supertraining Institute.