A Physio's Guide to Plyometrics

For many physiotherapists, plyometrics are considered outside of their wheelhouse. However, there has been promising research of late indicating significant health and performance benefits one can glean from an appropriate plyometric training program. Of interest clinically are the improvements in bone mineral density (1), decreased risk of falls in the elderly (2), improvements in tendon properties (3), improved running efficiency and speed (3-5), and improved general overall sporting performance for athletes (3,5,7).

For this reason many physiotherapists are now looking to upskill themselves in the area of plyometrics. Understanding the scalable continuum of both upper limb and lower limb plyometrics can allow clinicians to optimise the rehab process I outlined in my previous blog on the rehab continuum (8).

Plyometric exercises lie along a continuum of intensity in terms of the biomechanical forces placed on the body. This can even change with subtle variations to the same plyometric exercise. Therefore you really are only limited by your imagination in designing appropriate plyometric exercises for the goals of your patient or athlete.

The Three Components of Plyometrics
Before we get too deep on plyometrics let’s refresh ourselves on the basics.
Plyometric exercises are generally described in three phases of musculotendinous unit action:

Eccentric
This is the phase where the musculotendinous unit deforms under load created by a rapid stretch. During this stage kinetic energy is being used to create strain on the series elastic components of the muscle-tendon unit (MTU). During this time the muscle will be mostly acting to stiffen the tendon with an isometric pre-contraction, then eccentrically lengthen slightly as the joint angles change.

Amortization
This phase is the transition between the eccentric and concentric phases. This is where kinetic energy is transferred and stored as elastic potential energy relative to the degree of tendon stiffness or compliance. You can think of this as the loaded spring ready to rapidly bounce back to its length. The quicker this phase, the more of that elastic energy will be transformed back into kinetic energy for the upcoming concentric phase. Muscles are working isometrically here to facilitate the spring like tendon.

Concentric
This is when that stored elastic potential energy converts back to kinetic energy, and combines with the associated conscious and reflex muscle contraction forces. The end result is explosively propelling the systems centre of mass in the applied direction (3,6,7).

Clinical Pearls for Practice
“Quicker / more explosive” plyometric performance will be indicative of: Strong effective pre-contraction
‘Stiffer’ tendon
Low – moderate eccentric phase joint angle changes
Quicker amortization phase

“Slower / more controlled” plyometric performances will be indicative of the opposite:
Lower magnitude of pre-activation
More compliant tendon
Higher eccentric joint angles
Slower amortization phase

Knowing this becomes important when rehabbing athletes for different sports which prioritise different plyometric qualities (e.g. a beach volleyballer vs a hurdler).

Plyometric Progressions
I generally split plyometric prescription into four phases. These act as checkpoints along an intensity of loading spectrum.

Any plyometric exercise sits somewhere along this spectrum exhibiting traits closer to one phase or another. Below is a pictorial example of different plyometric exercises, and the specific biomotor qualities they train (7).

Force Absorption Phase
This phase is centred around the eccentric portion, teaching the patient how to decelerate the systems mass in the most safe and efficient manner. For risk mitigation we want to have first performed our clinical examinations of the area, as well as a few pre-requisite functional assessments. Before beginning this first stage of plyometrics the patient should have:

Minimal pain
Minimal swelling
Close to full ROM
Muscle strength and endurance > 60% of unaffected side
Lower limb:
- good single leg balance (eyes open > 30 seconds) - good neuromuscular control (maintain good alignment during single leg squat – half depth)

This phase consists of very basic exercises:
Lower limb – tall to short landings, altitude landings, running mechanics retraining, falling start catches
Upper limb – incline falling pushup catch, catching a ball

To progress difficulty in this phase you could increase the height of landing drills, add an external load, or even a perturbation to balance. The main goal in this phase is to build robust, unbreakable desired deceleration movement patterns to achieve the goal task.

Force Creation Phase
This phase is the beginning of assessing and coaching the concentric portion of a plyometric movement, as well as the use of a single amortization phase.

Performing bilateral and unilateral maximal broad jump and vertical jump assessments at the start of this phase can be useful for programming and risk identification. To be confident in being able to program exercises in this phase I like to see a 70% LSI in muscle strength.

Whether you are performing vertical force creation exercises (such as seated vertical jumps) or horizontal exercises (such as broad jumps), the patient will be having to finish with a less controlled higher force eccentric phase. So having achieved competence of the prior phase can be reasoned to be a good prerequisite in most cases.

This phase consists of the following types of exercises:
Lower limb – seated vertical jump, box jump, broad jump, single hop, olympic lift pull derivatives
Upper limb – single rep plyometric incline push up, med ball shot put

To progress difficulty in this phase you could increase height, length or load.

Stretch-Shortening Cycle Phase
This phase involves the real assessment and progression of the musculotendinous unit towards the movements specific to athlete’s goals. This is where we put multiple contacts together of some of the previous movements in a single rep. Here we are testing the efficiency of the stretch-shortening cycle to store and release energy through multiple controlled contacts.

The assessments we have previously performed should be close to 90% LSI and we can even do some multi-contact assessments (e.g. triple crossover hop) to help guide programming and progress.

Be sure to watch force absorption and creation strategies as the number of contacts per rep increases (e.g. the second landing and hop of a triple hop may use a different strategy to the first). There will likely need to be lots of coaching to ensure the appropriate strategies are used.

This phase consists of the following types of exercises:
Lower limb – skips, bounds, multi-contact hops, skater hops, barbell squat jumps, power cleans
Upper limb – plyometric push ups, push press, med ball catch and throws

To progress difficulty/intensity in this phase you could increase height, length or load.

Maximal Demands Phase
This phase is where we want to bulletproof the patient for returning to their goal activity. Here we should be assessing and training towards the capacity to handle higher than task-specific plyometric intensities.

All previous assessments should be greater than 95% LSI and we should be testing competence in goal-specific tasks.

The level of control: chaos in the plyometric exercises should be leaning in favour of chaos (i.e. more dynamic and reactive). Here we should be checking for how robust the previously built motor patterns are under the highest levels of intensity.

This phase consists of the following types of exercises:
Lower limb – depth jumps +/- subsequent jump, sports specific jumping / landing, e.g. AFL marks (for any Aussies out there!), multidirectional multi-contact hops
Upper limb – shoulder hops, push jerks, reactive cuff catches, reactive wall ball bounces

To progress difficulty in this phase you could increase height, length or load.

Prescribing Plyometrics
So we know what plyometrics are, and that there is a continuum of exercise intensities across the four phases above, but how do we actually prescribe plyometric loading?

Luckily there has been some work on this and I like to split it into two different types of prescription here.

‘Plyometrics only’ programming:
Beginner – 80-100 ‘contacts’ per week
Intermediate – 100-120 contacts per week
Advanced – 120-140 contacts per week
Split across 2-3 sessions per week, with minimum 48 hours between sessions

Mixed model programming (plyometrics + other training):
Per session: 2-5 sets, 1-6 contacts per set
2-3 x per week, with minimum 48 hours between sessions

Remember to balance stress throughout your athlete’s programs. So if your athlete is doing a plyometrics only program their volumes (number of contacts) is able to be a lot greater than if they are doing plyometrics amongst a more holistic training program (6).

Conclusion
By having a solid understanding of plyometric assessment and prescription, physiotherapists can take their clinical reasoning around exercise prescription to another level. With the health and performance benefits from a well integrated plyometric program now evident, I think it’s time physios “spring into action” and become experts in the therapeutic use of plyometric exercise.

Physiotherapy Westville