Plyometrics for Sport Performance◆ ☕️☕️☕️ 17 min read
- Stretch Shortening Cycle
- Plyometric Intensity
- Intensity Scale of Plyometrics
- Plyometric Exercise Specificity
- Plyometric Periodization
Plyometric exercises are traditionally activities that involve rapid and powerful jumping or hopping motions that are preceded by a preloading countermovement. These include different depth jump and countermovement jump variations.
The benefit most associated with plyometric training is the development of power, which can then be linked to increases in agility and sprint performance, along with improved running economy, if plyometric training is implemented appropriately.
As the adaptations to plyometric training primarily take place on the level of the nervous system, morphological changes are not so common with such training.
Stretch Shortening Cycle #
The stretch shortening cycle (SSC) is the key mechanism behind plyometric exercises. The SSC is a type of muscle function in which the muscle is stretched and then immediately shortened. This sequential eccentric (lengthening) and concentric (shortening) muscle action will allow the muscle to produce a more powerful output than what is possible only by shortening it. The SSC is a natural phenomenon that improves our efficiency in activities like running and jumping, but also in throwing actions, as the SSC is not unique to the lower limbs alone.
Some of the main factors contributing to the SSC effect include:
- Storage and utilization of elastic energy
- Increased motor unit recruitment
- Increased force development throughout the eccentric phase of the SSC
- Muscle spindle reflex mechanisms
In case you'd like to read more about those mechanisms, I've mentioned them in my earlier article on strength and power development.
The exact factors contributing during a plyometric exercise depend on the specifics of the exercise itself.
For the elastic energy to contribute, the transition period between the eccentric and concentric phases must be short.
For increased motor unit recruitment to weigh in, the eccentric phase must be minimal and the transition period between eccentric and concentric phases short.
To allow for increased force development, the eccentric phase must be slow.
For the muscle spindle reflex to contribute, minimal stretch has to occur during the eccentric phase of the exercise.
Some of those characteristics can happen concurrently, but the rate of eccentric loading required is a distinguishable factor between different plyometric exercises. Minimal eccentric stretch is required for the power of muscle spindles to kick in, but a slow eccentric is necessary to allow for increased force development throughout the eccentric phase.
Based on that distinction, SSC is classified according to ground contact time, with fast SSC having a less than 0.25s ground contact, and slow SSC having a longer than 0.25s ground contact time. Fast SSC activities are usually elastic, reactive jumps, such as repeated hops and depth jumps, whereas a slow SSC activity could be a countermovement jump.
Fast SSC has shorter eccentric phase and a quicker transition from the eccentric phase to the concentric phase. Slow SSC is the opposite – the eccentric phase lasts longer, and the transition is slower.
As stated by Eamonn Flanagan, the level of performance enhancement from the SSC reflex is dependent on the speed of the eccentric phase and the transition time. As such, greater power outputs and rates of force development occur with fast SSC plyometrics, whereas greater total force is achieved in slow SSC plyometrics. This comes back to simple physics – in case of slow SSC plyometrics, the ground contact times are longer, which allows for more time to produce force.
An important thing to remember about fast and slow SSC plyometrics is that they are not necessarily related. Having great slow SSC abilities does not automatically mean good fast SSC capabilities. As such, both of those qualities require separate attention in training.
This also has implications for performance testing. A variation of a vertical jump test has been a popular choice for decades, to test athletes’ lower body power. In terms of the SSC action governing maximal vertical jumping, it’s a slow SSC exercise. If reactive strength (fast SSC) is also of relevance to the sport, this quality needs to be trained as well as tested in a more specific way. A drop jump test variation could be a consideration here.
The comparison between fast and slow SSC also shows how slow SSC is better related to relative maximal strength abilities, whereas fast SSC reflects more the reactive and elastic abilities of the athlete.
Therefore, you might have a strong athlete who demonstrates adequacy in a slow SSC-based test, like a vertical jump test, but never really exceeds in elastic or reactive movements. If your testing protocol is not sensitive enough to provide insight into both slow and fast SSC function in a context where both of those are of relevance to performance, you are failing as a coach. This example further highlights the necessity to differentiate between slow and fast SSC abilities in performance athletes.
Plyometric training approaches are often dominated by slow SSC movements, because such is the nature of the majority of traditional jump exercises. Conscious efforts are required to make sure both slow and fast SSC work is incorporated into an athletes training plan. Then, you can tilt the scales towards which quality needs more emphasis. But fundamentally, both should be trained.
When reactive strength is the overall aim, the coach needs to think how much strength the athlete actually requires. From a biomechanics perspective, the interactions between the hip, knee, and ankle joints need to be considered. Reactive strength requires effective force transmission into the ground. The athlete's hips and knees can be very strong, but if the ankle joint integrity is lacking, they will leak force on ground contact. The opposite is also true. The athlete can have superb calf-achilles complex integrity, but the improvements from reactive strength training will still be limited if the hips and knees lack overall strength and power. The coach needs to make a decision on what is the limiting factor.
The work of Eamonn Flanagan has demonstrated a positive correlation between maximal strength ability and reactive strength. The research found stronger athletes to demonstrate better reactive strength ability on average. But even then, only close to 60% of reactive strength performance was found to be associated with maximal strength qualities. This brings us back to the discussion about the trade-off between the ankle, hip, and the knee. Having strong hips and knees as a result of traditional strength training could contribute to your reactive strength ability, but without proper ankle complex integrity, your elastic ability will not be optimized.
The above presented data still doesn’t imply that correlation means causation. It remains unclear if strength training directly improves reactive strength or vice versa. It could be assumed that strength-trained athletes are better able to tolerate the eccentric loads involved in intense plyometrics due to the positive effects of strength training on tendon strength and stiffness. This might be one of the reasons why reactive strength and traditional strength training seem to be associated.
Additionally, the demands of the sport are a crucial consideration when determining the overall importance of reactive strength. Sprinters strongly rely on reactivity, as they need to transmit high forces into the ground on every foot contact with minimal ground contact times. Combat sport athletes might only require reactive strength development to a certain degree, after which the ability to maintain that level of reactive strength becomes more important. The specifics of the sport determine the type of training necessary.
Based on what has been presented and suggested by Eamonn Flanagan, the best approach is likely to develop both reactive strength qualities and general strength alongside one another, with the focus directed towards the area which needs the most improvement.
For the sake of simplicity, coaches often like to set rules, like “If an athlete can’t at least squat 1.7x their own bodyweight, they are not ready for plyometric training”. This is a short-sighted approach that simply takes away a tool from your toolbox to use with your athletes. There is likely no such threshold for part-take in plyometric training. For the weaker athlete, you just tilt the scale towards more strength training and make this the focus, while avoiding high intensity plyometrics. That doesn't mean complete avoidance of all and any plyometric exercises. Low to moderate intensity fast SSC work should still be included to develop reactive strength qualities, if those are required.
To be able to distinguish between low, moderate and high intensity plyometrics, we need to define intensity.
Plyometric Intensity #
Plyometric intensity can be defined as the stress the plyometric exercise places on the body in terms of the muscle, connective tissue and joints involved. Intensity is determined by the eccentric loads involved and the time period over which the eccentric loads are applied.
Both the jumping and landing parts of a plyometric exercise affect its intensity.
Plyometric intensity is a key variable in constructing a safe and sustainable training plan that leads to intended training adaptations.
The guidelines for plyometric intensity as described by Eamonn Flanagan and William Ebben can be listed as follows:
Single leg plyometric exercise is more intense than the same exercise executed bilaterally.
Fast SSC activities are typically more intense than slow SSC exercises. This is due to shorter time period of force application, which leads to greater rate of loading.
Performing repetitions of a plyometric immediately after each other will cause higher total landing stress than performing individual repetitions with full landings and a brief pause between repetitions.
The height of the plyometric in terms of a jump up or down from (depth jumps) will impact the intensity of the plyometric. An athlete who is able to jump higher during the same plyometric exercise than another athlete will experience more stress upon landing.
Plyometric activities which incorporate arms into the motion will increase the height of the jump and thus lead to greater stress upon landing.
Some jumps in place, like tuck and pike jumps, also have higher landing stress due to high knee joint reaction forces, which might have to do with the aggressive extension just prior to landing. That is an important consideration, as these types of jumps are often categorized as low intensity, when in reality they are not.
Intensity Scale of Plyometrics #
Based on William Ebben’s work, an intensity scale for plyometrics can be constructed. In the order of increasing intensity this goes:
- Sub-maximal jumps/hops
- Concentric jumps
- Countermovement jumps
- Tuck and Pike jumps
- Drop jumps
- Fast SSC single leg jumps
Sub-maximal Jumps/Hops #
The entry level point to plyometric training is sub-maximal jumps and hops. These could be either slow or fast SSC, but have to remain sub-maximal. These can help develop technique and the athlete’s tolerance towards the demands of plyometric training.
It is crucial to make sure the athlete has robust landing technique in fast and slow SSC-type activities before advancing towards higher intensity plyometrics. As such, the cue of “sticking” the landing is often used when starting with sub-maximal plyometrics.
On the fast SSC side, exercises like pogo jumps could be utilized, with the emphasis placed on short ground contact time over jumping for maximal height.
Box jumps are also of relevance to use at this stage, as jumping onto a box minimizes the landing stress associated with plyometrics. Box jumps might not be the best exercise to develop maximal slow SSC function, as landing on a high box is often done in a “deep squat” position. Still, box jumps can teach jumping and landing mechanics without the associated landing stress, but the box height needs to be low enough to allow for the athlete to land with good mechanics in which the hips stay higher than the knees (think quarter squat).
Concentric Jumps & Countermovement jumps #
Concentric jumps refer to jumps that do not utilize the SSC, such as a squat jump. Thus, the contraction times are slower and jump height is lower than that of the countermovement jumps. These two factors also reduce the rates of jumping and landing forces experienced during concentric jumps, making them lower intensity than countermovement jumps.
Tuck & Pike Jumps #
As mentioned in the guidelines, tuck and pike jumps have higher knee joint reaction forces in comparison to concentric and countermovement jumps. As such, they are placed more towards the higher end of the intensity scale. The stress experienced from tuck and pike jumps is further amplified when they are performed in a “repeat” effort as opposed to performing single repetitions. In such a case, they may even be more intense than single effort drop jumps.
Drop Jumps & Single leg jumps #
Drop jumps are definitely a high intensity plyometric activity, more so when the drop height exceeds the athlete’s vertical jump height. This is further amplified through single leg variations, in which the high eccentric loads are being isolated to a single leg. This in addition to the short time frame in which landing and jumping forces are absorbed and applied makes the single leg fast SSC jumps very intense plyometric exercises.
In addition to having an understanding of how to categorize plyometrics based on their intensity, exercise specificity also needs to be considered when constructing a plyometric training plan.
Plyometric Exercise Specificity #
Exercises can either have general or specific effects depending on the context.
J.B. Morin has referred to two general strategies in which sport performance can be enhanced:
- Increase physical output (force production)
- Increase efficiency of physical output (force application)
He explained this through the example of sprinting, in which specific skipping and bounding drills could be used to enhance the efficiency of physical output, whereas general strength training and plyometrics could be incorporated to increase physical output in general.
Based on this idea, general training is aimed at increasing the overall force production or rate of force production abilities. Specific training is aimed at optimizing the application of the produced force. Both are essential qualities to train in athletes.
Every exercise exists on this continuum from general to specific, with the main consideration being the similarity of the biomechanics of an exercise in relation to the sporting activity we are trying to improve.
Eamonn Flanagan uses 4 areas to compare the correspondence of plyometric exercises to sporting activities:
- Does the plyometric exercise have similar ground contact time to the sporting activity?
- Does the plyometric exercise generate force vertically and horizontally in a similar way to the sporting activity?
- Is the plyometric exercise bilateral or unilateral? How does this relate to the sporting activity?
- Is the plyometric a single effort or repeated effort exercise? How does this relate to the sporting activity?
Returning to the sprinting example, we could look at different plyometric exercises in relation to the 4 areas outlined. A drop jump, for example, does not correspond well with sprinting. Drop jump is bilateral, sprinting is unilateral. Whereas drop jump is a fast SSC activity, the ground contact times in maximal velocity sprinting are even shorter. Drop jump is a vertical activity, whereas sprinting also requires a strong horizontal force component. Sprinting is also more repeated effort than a drop jump. This makes a classic drop jump exist more in the "general" end of the continuum in relation to sprinting motion.
Drop jumps can still be used to produce very high forces against the ground in short contact times. Such activity is a strong stimulus for fast SSC reflex, contributing towards base level neuromuscular adaptations. Such adaptations will allow the athlete to express high rates of force production in more specific activities further into the training plan.
Alternatively, there are ways to make the drop jump more comparable to sprinting. The drop jump could be performed on one leg from a box height more relevant to sprint mechanics along with shorter ground contact times and potentially a forward bound to improve horizontal force production abilities too. Such modifications would shift the drop jump more towards the "specific" end of the continuum and make it more resembling of sprinting actions.
Regardless of how the drop jump is applied, both general and specific exercises have a place in training context. Referring back to J.B. Morin’s two principles, increasing both absolute force production and the efficiency of force application are necessary to optimize performance.
Plyometric Periodization #
While there is no such thing as one optimal approach to plyometric exercise periodization, Eamonn Flanagan has come up with a 4-phase framework that provides an overview of the principles on how to periodize plyometric training.
Phase 1: Foundation #
The foundation phase is all about teaching the athlete technique. That involves how to land, jump and hop effectively. Even if fast SSC reactive strength is the ultimate goal of training, slow SSC activities can still help with jumping and landing mechanics. Additionally, jump landings could be used to develop eccentric strength. Thirdly, the use of low intensity fast SSC activities such as pogo hops can be included to introduce the athletes to reactive movements. As mentioned earlier, these should be kept sub-maximal and short ground contact times should be emphasized over jumping for maximal height. The hopping could be done in short series of up to 20 repetitions per set. Skipping and low intensity bounding variations could also be included here.
Phase 2: Development #
The development phase is where fast SSC exercises start moving towards moderate intensity. Hops could still be included, but a low hurdle could be used to jump over to incorporate jumping a bit higher than before, while still remaining in the sub-maximal realm of training. Still, short ground contacts should remain the emphasis. Postural control is also key, with the athlete needing to keep a tall strong posture throughout the hopping actions without collapsing during the activity.
For field sports athletes, this phase might also include change-of-direction (COD) activities. These could take the form of multi-directional hops over low hurdles or lateral pogo hop series. COD activities apply shear forces to the joints involved, making proper joint alignment and body control crucial to stay healthy. The COD activities could be started in a slow SSC fashion with full landings and longer ground contact times to ease into it.
The developmental phase is also when reactive strength endurance work should be introduced. This simply means the incorporation of longer series of 30-50 repeated sub-maximal low-to-medium intensity hops or skips. The “extensive” work helps to condition the ankle stabilizing musculature, which according to J.B. Morin, are used to fatigue and thus only doing short series will never really challenge them.
Phase 3: Realization #
As the name of this phase implies, we can now advance to high-output, maximal-effort reactive strength training. General fast SSC activities like drop jumps or maximal effort repeated hops are ideal. The aim is to apply a strong overload stimulus to improve fast SSC mechanisms. Short ground contact times and maximal jump height is to be emphasized.
In this phase, we need to start looking for more specificity to assist in the transfer of the developed qualities to the specific sport. Coming back to the sprint example, drop jumps can be made more specific with the goal of enhancing sprint performance in mind. To satisfy the COD requirements of a field sport athlete (in case they are not doing enough COD work in their technical sports practice already), high-intensity multi-directional fast SSC activities could be used here.
It’s important to not lose focus of the fact that sports training will at the end of the day be the most specific form of training for the athlete. Incorporating specificity into plyometric training can assist the overall sports training by helping to overload specific aspects of performance. But you will never replicate the actual sport.
Phase 4: Transfer #
The final phase is all about training transfer to actual performance. As such, unilateral, horizontal, or multi-direction plyometrics may remain the main emphasis of this stage due to increased specificity. Maximal effort should be continued when performing those activities, as this is what sporting contexts require.
It is important to note that whereas these phases have been explained as by separate entities, there should be a flow to phase transfer. The switch from one phase to the next should in no way be abrupt. Depending on the individual athlete’s needs, some elements of activities introduced in the earlier phases might be taken further into following stages if that reflects an existing weakness of the athlete. The phase lengths may need to be varied depending on in which phase a particular athlete needs more work or how fast they are able to progress through the phases. Some might need more foundation work due to the lack of such training in the past, whereas others might be able to progress faster.
In terms of the training frequency and training volume for plyometric training, 2 plyometric sessions per week can be effective. At least 10 weeks of plyometric training with 20+ total training sessions will be required to maximize performance improvement. The phases that incorporate high-intensity plyometrics (phases 3-4) should have around 50-60 jumps per session to maximize the training adaptations.
Again, keep in mind that the phases outlined as described by Eamonn Flanagan are in no way supposed to be used as a rigid structure. You might have a long-term plan in how to progress the plyometric training for a specific athlete, but it should still be modified and adjusted along the way. Don’t stick to this exact model. Take the underlying principle presented and apply them in a context specific to you.
Whereas this article is entirely focused on the presence of SSC in the lower limbs, it is important to note that such a function also exists in upper-limb movements, i.e. during throwing actions. How to make the most of upper body plyometric activities, commonly through the use of medicine ball throws, is an entirely different discussion and would add pages to this article. As such, it is best kept for another time.
As referred to throughout the text, the ideas presented belong largely to Eamonn Flanagan, William Ebben, and J.B. Morin. All credit to those great men.