Plyometrics Re-Explored

Back in 2017, I wrote an article about plyometric training. The aim of that post was to introduce plyos, outline the mechanisms at play and to showcase their relevance to tennis performance (from both a research and practical perspective).

That article was a good starting point. It highlighted the diversity that exists when we look at tennis movement...and how plyos, because of their versatility - ie. they can be performed in a multitude of directions, velocities, amplitudes etc - might very well be the most important ingredient when it comes to better on-court movement. On top of that, we looked at the research that supports plyometric training…and even if it’s not always robust or transferable to real world settings, that research does favour the incorporation of plyometrics with athletes across all sports (including tennis).  

Lastly, that older post was heavily influenced by the work of Eamonn Flanagan - a researcher and strength coach (Irish Rugby, Munster and others) - who I was fortunate to spend some time with during my masters studies in Edinburgh back in 2010/11. In particular, he was the first to introduce the SSC (stretch-shortening cycle) actions, and in particular, how different plyometric activities fall into 2 broad categories - fast SSC (below 0.25s) and slow SSC (above 0.25s). 

So if you haven’t yet, I still think you should read through that post as it covers a lot. But I will admit this…I misspoke on a number of topics. Here are just a few:

1. Ground contact times (GCTs) greater than 0.25s are NOT plyometric. The time on the ground is too long - in other words, even if we’re performing a jumping action (and even if that jumping action is performed in a repeated/continuous manner), we’re not benefiting from stored elastic energy. It turns out that these types of movements (which we will explore in greater detail) are actually more ‘strength’ oriented (McInnes Watson 2021 - not yet published).

2. On top of that, given that long/slow SSC movements aren’t plyometric, they are NOT a precursor to more reactive and intense plyometric activities (which is what I recommended in that previous post). In fact, we likely need more diversity early on in the training process; incorporating a mix of low, medium and yes (in some cases), even high intensity plyo movements. And performing ‘stick landings’ - which are seen all over social media - are NOT a necessary starting point when it comes to plyos (or at any point during the training process for that matter). 

3. We don’t need hurdles, boxes or cones for plyometric training to be effective. In fact, as my colleague (and PhD plyos specialist) Matt McInnes Watson has iterated on a number of occasions, athletes actually improve certain qualities to a greater degree without them. Take reactive strength as an example. When subjects self-selected their jump height (off of a box), compared to landing on another box (a typical depth jump), their reactive strength increased more so in the former, compared to the latter (dialogue with McInnes Watson 2021). 

4. Jump training is NOT plyometric (that’ll be debunked). 

5. Intent does not always have to be maximal to get a plyometric effect. Different types of jumps, at different intensities, amplitudes, and with larger or small emphases on either vertical or horizontal displacements etc, will elicit highly different adaptations at the tissue level. These adaptations will inevitably have differing impacts on various performance measures. 

But since I wrote that first post over 4 years ago, a lot has changed. With the help of individuals like Dan Pfaff, Boo Schexnayder, and most recently, Matt McInnes Watson, I’ve come to the realization that because there are endless variations when it comes to plyometrics, simply using a fast vs slow SSC to distinguish between various movements and ground contact times, just isn’t enough. 

To that point, in this 2-part series I’m re-exploring plyometric training in greater detail. In this first post, we’ll look at the 6 phases that every plyometric movement must possess (for it to be classified as a ‘true’ plyometric), simplifying the science behind plyos and how tennis movements are enhanced via plyometrics. 

First a Little Background Info

When I first saw Dan Pfaff’s (elite sprint coach + educator at Altis) workouts, his jump circuits opened my eyes to the variations that exist when it comes to plyometric training. From in-place volume-based movements, to high intent bounding - even low level hops - seeing all these movements performed in different directions, through all 3 planes of action, with deep amplitudes or shallow and stiff responses. It was the starting point for me where I said, “ok, there’s a whole lot we can do here, and each type of plyo movement will surely elicit a highly different adaptation at the tissue level”. 

I was also drawn to Boo’s programs because of how similar they were to Dan’s (I think Dan was Boo’s mentor if I’m not mistaken). But some of his thoughts on how to organize plyos - within the training week but also the calendar year - were really intriguing. While many coaches fear doing intense work pre-season or in-season, Boo argues that this is a must to not only maintain high levels of tension throughout the system, but to vaccinate the athlete from injury (of course dosage matters...and more is certainly not the answer here). 

Then there’s Matt McInnes Watson - who I’ve started calling Verkhoshansky Jr. (for those who have some background in sport science history, you know who I’m referring to...Verk is the godfather of plyos). 

Matt has perhaps the most simplified system when it comes to organizing and implementing plyometrics with athletes, but still the most expansive. The actual exercises aren’t much different than those used by Dan, Boo or others - but he has completely expanded upon them and created a classification system that makes the most sense to me (and many others who are incorporating them). 

But before we get into the variations - and how they affect tissue adaptation, it’s a must that some aspects of plyos be addressed. Note - I have a lot of readers who are parents, juniors and club/rec tennis players so I don’t want to make this too complex (forgive me if I haven’t/don’t accomplish that) but it’s important we dive into some science here. 

Plyometric Phases Re-Defined

Plyometrics originally encompassed 5 phases (this was introduced by Yuri Verkhoshansky in the 1960s). However, Matt McInnes Watson - based on anecdotal and research findings - believes there are actually 6 phases (or at least 2 parts to phase 1). Below we will outline each phase (with my interjections in italics):

1. Initial Momentum Phase (IMP): The body moves due to the kinetic energy produced from a preceding action.

   • This ‘preceding action’ could be a jump of some sort, a run or sprint, a drop of some kind etc. If we do NOT have this phase, the movement as a whole cannot be considered plyometric (think depth jump vs countermovement jump).

2. Pre-Activation Phase (PaP): Due to profound research around the area, the IMP could also include a pre-activation/anticipation phase (PaP) of the lower extremities up to 0.20s prior to landing (Kannas et al, 2012; Viitasalo et al, 1998; Nigg and Wakeling, 2001). PaP has been found to bring about generalized muscle stiffness. Flanagan and Comyns (2008) commented on the pre-activation (PA) and pre-tension of certain muscles before the point of contact. It was seen in some cases that the lower extremity musculature may be 40-80% activated at the time that the foot touches the ground (Hewett et al, 2005; Nigg and Wakeling, 2001). This anticipation in the body comes from wanting to hit the ground actively, so that tissue structures are ready to withstand high levels of force (from McInnes Watson 2021). 

   • All you need to know here is that you’re basically in the air (or at least one limb is) and there’s this ‘pre-jump’ activation that occurs. We often ask our players to think ‘jump’ just prior to landing - which has a good effect on creating stiffness in order to get the desired response once we actually hit the ground. Matt often cues his athletes to ‘attack’ the ground (again, this has to be done while the foot is in the air, just prior to hitting the ground). 

3. Electromechanical Delay Phase (EDP): Coined to mean the start of the electrical signal to the start of the mechanical contraction in a muscle. Some may define this phase to include the lengthening of the series elastic component (SEC) of the muscle complex.

   • From what Matt has observed, read and written about, the EDP is when we initially contact the ground. The Electromechanical Delay is then based on how long it takes for the brain to register things and understand force. Interestingly, Matt believes there is an intricate relationship between the PaP and EDP. In fact, if we have an effective pre-activation prior to landing, Matt believes the delay may not be as prominent (contrary to what research suggests). This makes sense doesn’t it? Essentially, how we approach a landing (or put better, how we approach attacking the ground), will have an impact on how the brain interprets that response. 

4. Amortization Phase: When kinetic energy produces a powerful myotatic stretch reflex. This phase bridges the eccentric and concentric phases of a landing and takeoff.

   • This is the time in which the foot (or feet) are in contact with the ground, in an isometric manner. There seems to be this threshold when it comes to plyos - if the total contact time is under 0.25s, it’s considered a plyometric activity, remember. If it’s above 0.25s - and you’re still not off the ground - it’s perhaps more of a ‘ballistic’ activity (there’s a much higher reliance on strength in this case, rather than the elastic response we’re aiming for with plyos). Verkohshansky initially termed a movement plyometric if the amortization phase itself was under 0.10s. This, however, is very difficult to measure - which is why total ground contact times are generally used to classify different types of plyos. 

5. Rebound Phase (RP): This phase marks the release of elastic energy from the SEC, together with the involuntary concentric muscle contraction.

   • This is the result/response of the previous phases and the subsequent final concentric ‘push’ that enables us to get off the ground - and to produce the desired movement. 

6. Final Momentum Phase (FMP): When the concentric contraction is complete, and the body continues to move by means of kinetic energy from the Rebound Phase. This phase will then restart the cycle in preparation for the next movement.

   • This is the resultant airborne phase (which is influenced by the preceding phases...and in particular, the EDP). We can no longer influence the resultant jump (it’s height, direction, velocity and so on). 

Plyos Simplified 

Perhaps the easiest way to think of plyometrics however, is what McInnes Watson calls a ‘landing to take-off’ (L-T) action - which should occur in a relatively short time frame. So anytime we have this repeated landing to takeoff action - one that is preceded by the IMP (look above to refresh your memory on this phase), we’re performing a plyometric activity. 

That’s step 1. If we don’t have a L-T action, we don’t have a plyometric movement. In part 2, we’ll go into more detail why this is the case - this will include examples (and the reasoning behind why a countermovement jump isn't plyometric...even though it’s a jump). 

Step 2 to simplify plyos is to look at ground contact times - they should NOT be above 0.25s. While simple in theory, this is perhaps harder to see if one is not experienced in this realm. It might be easier to determine whether a movement is NOT plyometric, than whether it is. 

The two questions I ask myself here are: a) what are the amplitudes (or ranges) at the knee during a jump - if they are deep/large, it probably means that we’re spending a fair amount of time on the ground. Result, not plyometric. And b) is the athlete struggling to maintain joint stability during these repeated L-Ts? If so, it’s likely that this joint distortion is forcing the athlete to stay on the ground longer (just to keep his/her balance). Again, not plyometric. 

Hopefully that simplifies things a bit. But what about classifying plyos that fall under 0.25s? Because below this threshold, we can benefit from highly differing adaptations at the tissue level. A GCT of 0.24s will be hugely different compared to one that is 0.10s. 

The question is, do the exact values matter? For most sports - team + court (like tennis), we probably don’t need to be overly concerned with that type of precision - for one important reason: 

A sport like tennis is highly reactive + open-chain (i.e. there’s a massive perceptual demand). And the movements will vary greatly - sometimes we need a higher emphasis on lower shank stiffness. Other times we need more of an elastic response. Often, an explosive concentric action might be of higher importance in a given on-court situation. All that means is that our plyometric training likely needs to be really diverse. That’s why Matt’s classification system (which we’ll explore in part 2 of this series), is so simple and effective. It tackles the entire plyometric spectrum - so we know, more or less, which type of quality we’re training.

Note - in certain sports (track & field rings a bell), knowing exact values is probably a lot higher on the KPI list as it may determine the difference between crossing the finish line 0.1s faster (or slower), or jumping a cm higher (or lower)….and those differences matter.

Plyos Re-Explored Part 2 - What to Expect

Let me briefly illustrate a point using the split-step. Does a tennis player utilize the fast SSC during split-step actions? And is it a worthwhile pursuit to train this ability off the court? The answer to both of those questions is a resounding yes! I’ve argued before - and I’ll do it again - the split-step is perhaps the most important movement quality a tennis player must possess (so much so that I dedicated 2 sections to it in the movement module of my e-course). And for me, there is no better way to improve the underlying qualities of the split-step, then through plyometric training. 

Apart from the split-step, there are many other ‘sister’ and ‘brother’ movements in tennis that utilize the SSC - those too are best targeted via plyos. But each of those movements have variations in terms of power outputs, tissue/muscle activations, tensions, velocities and so on. 

That’s what we’ll look at in part 2. Not only will we classify the various plyometric activities - based on the work by McInnes Watson - we’ll also highlight movements in tennis that will be accentuated as a result of plyo training. 

Lastly, we will also cover some do’s and don'ts when it comes to implementing plyos (including technical considerations) while debunking ‘other’ forms of jump training (a lot of what you might see on social media that truthfully, is a good way to make someone tired...but not elastic...which is what you should see via plyos). 

Saying that, just because a movement isn’t plyometric doesn’t mean it cannot be implemented into a tennis player’s program. It just means that we’re not getting the ‘alleged’ adaptations that plyos have to offer (which means you might be using exercises in your program for a certain benefit, but in reality, it’s not what you’re getting out of it). 

Ok - I know that was a lot to take in but if you stay/ed with us, I’m confident your training programs - and ultimately, your on-court movement - will majorly benefit. 

Also, if you're looking for more practical plyometric training info, I strongly urge you to have a look at PhD Matt McInnes Watson' Plus Plyos platform. It includes hundreds of plyo exercise variations, a number of structured programs - and he's created a massive discount for Mattspoint readers. Take a look - and follow Matt on Instagram for daily plyo insights.

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