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Introduction
How are Michael Jordan's ankles, your car's suspension system, and jumping off wooden boxes related to each other? The answer is found in the 'plyometrics' section of most decent strength and conditioning programs.
If you want to jump higher, sprint faster, and generally produce more power (which is defined as force in a given time) in athletic endeavours, it makes sense to have practised and honed that ability in training.
Plyometrics can play a key role here, but they are often misunderstood, loosely defined, poorly programmed, and carried out at a sub-par standard. But when planned and implemented correctly, they provide an opportunity for you to experience previously unavailable adaptations and performance enhancements.
Depth Jump Exercise: The Original Plyometric
History
The Big Names
Yuri Verkhoshansky was a Russian track and field coach, who implemented various revolutionary approaches with his athletes. For example, he was one of the first coaches to consider strength training to be an important part of a runner's training program. But his most well-known contribution was the 'Shock Method'. This involved using exercises like the depth jump and repeated hurdle jumps to create a dynamic contact with the ground, from which his athletes would have to rebound as quickly as possible. Olympic runner and coach, Fred Wilt, observed these obscure-looking training protocols, and the success of Verkhonshanky's athletes, and coined the term plyometrics. This type of training was popularised further by coaches like Michael Yessis, who has written many books on the topic. I include these names to direct you towards avenues for further reading if interested.
Debate Over Definition
Since the birth of the Shock Method and the subsequent naming and popularisation of plyometrics, the definition of what constitutes plyometric training has been debated.
In keeping with Verhoshanky's original Shock Method, true plyometric training requires the presence a reactive component, whereby there is a rapid eccentric drop immediately before any jumps or explosive movements, and where ground contact time is minimised. Think of a depth jump as the clearest example of this.
Many programs will include exercises like box jumps and broad jumps in the plyometrics section. While there can be a rapid eccentric component to these exercises (E.g. Throwing your arms down and loading the lower body joints quickly before jumping), these exercises don’t involve the impact element that a depth jump, for example, does. For this reason, some prefer to label these exercises as jump training, as opposed to plyometrics. Others see plyometrics as a broad category that includes the Shock Method as sub-section, and includes the other, less intense variations.
How Plyometrics Work
The Stretch-Shortening Cycle
Think of what happens when you drive over a speed bump too quickly. You hit the speed bump, forcefully compressing the springs in the car's suspension system, the springs react by expanding, and the car bounces upward as a result. All this happens in a split second.
In the same way, when you drop from a height and your foot hits the ground, the muscles and tendons in your lower body forcefully stretch, causing them to subsequently automatically contract in the opposite direction. This is part of what is known as the stretch-shortening cycle. This is the reactive component that differentiates plyometrics and produces their purported benefits.
The stretch-shortening cycle can be broken down into 3 stages.
The eccentric phase is where you first make contact with the ground, after a drop or a run-up, for example. Here, the muscles and tendons are forced to stretch, thereby building up tension and stored energy (like the suspension springs).
The second phase is known as the amortisation or transition phase. Here, signals are sent from the tendons and muscle spindles (cells in the muscle that detect changes in muscle length) towards the central nervous system, to indicate that there has been a stretch beyond the usual in the muscles and tendons. You can think of this as similar to the signals that would be sent to the central nervous system if you were to touch a hot stove, indicating that immediate reflexive action is required. In the case of the hot stove, the reflexive action is to remove your hand. This happens without you even thinking about it. In the case of a depth jump, for example, this reflexive action consists of the muscles and tendons forcefully shortening and contracting, in order to resist and overcome impact. This is known as the myotatic reflex.
The third phase is the concentric phase. This is where the muscles and tendons forcefully contract and shorten, assisted by a combination of the stored energy built up from the stretching of the muscles/tendons, and the reflexive signalling from the central nervous system. This reflexive signalling calls more high threshold motor units into action. These are motor units that are rarely used in everyday life, but which are essential to maximal force output. Plyometrics allow us to train these motor units, potentially allowing for increased access to, and better functioning of, them in the sporting context when they're needed.
Effect During that Exercise
This stretch-shortening cycle has the effect that you are able to produce more force in less time (that is, more power) than you would normally. This becomes obvious with an example: Imagine you were asked to attempt to dunk a basketball. Would you stand under the rim and try to vertically jump up? Or would you take a run-up? Of course, you'd take the run-up. The run-up means that that final step before jumping will involve a forceful stretch and contraction of the lower-body muscle and tendons, allowing you to jump higher. You might not have previously known that that's why you'd choose the run-up, but you should now.
Observe the final few steps, where the foot hits the ground forcefully, and the lower body is ‘loaded up’ before jumping.
Effect on Subsequent Exercises Within That Session
Using plyometrics also has the potential for what's known as a potentiating effect. Potentiation, in this case, means that performing a plyometric exercise can allow you to produce greater forces in exercises that come afterwards. Eg. Doing lying medicine ball chest throws before a bench press can help you bench press more weight.
This is thought to be due to the extra high threshold motor units recruited as a result of the plyometric exercise remaining active and available for use during the subsequent exercise.
Interestingly, this can also work the other way around, where performing a heavy strength exercise can improve your performance in a subsequent plyometric exercise. E.g. Doing a set of squats can improve your ability to jump high afterwards.
You can use this knowledge to prioritise whichever aspect you are hoping to improve more. If strength improvement is your goal, performing a plyometric exercise first could allow you to lift more weight, and progress further over time. If improving the explosive component of power output is your main goal, then performing a strength exercise before your jumps could be useful.
This concept has led to the development of contrast training, which I will cover in a future article.
Effect Over Time
Over time, the effect of performing plyometrics is that power output improves. There are many potential reasons for this. There is clearly a skill acquisition element, whereby you get better at what you practice. In this case, if you jump more, you're going to improve your ability to organise your body and jump 'better'. But there are also muscular and neurological adaptations. Routinely exposing the muscles to increased forces, as with strength training, for example, is likely to create a hyper-compensation effect, where the body prepares for upcoming exposures to those types of forces by increasing the muscles and tendons’ ability to withstand what's being asked of it. There is also the potential that routinely tapping into increased numbers of high threshold motor units will allow for enhancement and voluntary use of these muscle fibres in future.
Whatever the mechanisms, the increase in power seen as a result of consistent plyometric work can have a huge carry-over to athleticism, not only for those interested in improving top-end speed, acceleration, and jumping ability, but also those who are going for longer distances, where incremental improvements of force output per step can lead to improved performance in endurance events.
How to Implement Plyometrics
Introducing and Progressing Plyometrics - Intensity and Volume
Due to the high force outputs and neural demand associated with plyometrics, there is some injury risk associated with them if not programmed and performed appropriately (as with all exercises). With that said, if your sport or goals demand that you produce high forces through jumping, landing, sprinting, and turning then you may be increasing your injury risk by NOT including some element of this within your training.
But in the same way that you wouldn't load up the barbell as heavy as possible on your first time learning to squat, diving straight into the most intense plyometric exercises isn't a recommended approach.
Instead, introducing lower-intensity, higher-repetition variations will allow you to acquire the body awareness, skills, and muscle/tendons strength to begin introducing more intense variations down the line.
These lower-intensity variations (sometimes referred to as extensive plyometrics) could include exercises like pogo hops, skipping variations, and bounds for anywhere from 20-40 reps.
Over a period of weeks and months, you can start to introduce higher-intensity variations (sometimes referred to as extensive plyometrics). These could include exercises like hurdle jumps, box jumps, and eventually, more intense exercises like depth jumps. With this increase in intensity, you should reduce the volume (number of reps) you are doing, to avoid excessive fatigue. Towards the more intense end, your sets could be as low as 1-5 reps.
As you advance, there is no need to completely remove the higher-volume, lower-intensity plyometric variations. These can become a tool for continuing to develop general physical preparation of the joints and muscles, with low fatigue. You can include them as part of a warm-up, for example.
Sport Specificity
Whilst the benefits of implementing a general plyometric approach will likely carry over to most athletic endeavours, as your training becomes more advanced, it can be worth considering the specific demands of your sport or athletic goals.
This might include assessing whether your sport demands low- or high-intensity efforts of power output. For example, a long-jumper has a low number of maximally intense jumps to complete in competition, whereas a basketball player will have many sub-maximal jumps to complete through a game. This should be reflected in how they include plyometrics within their training.
Other aspects include whether you are likely to be jumping off one foot, two feet, or a mixture, as well as what planes you are likely to be moving in - are you always moving forward in a straight line, or will you be twisting and turning?
Finally, with all the above said, it is critical to remember that plyometrics should only make up one element of your training program. Most sports and athletic goals will comprise of a combination of strength, endurance, speed, body composition, movement capacity, and power, and so your training should contain elements of each, based on your goals and your current limitations.
Conor O’Neill, Know Yourself Performance
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