3.1 Introduction to Plyometrics

The short version

Jump onto a box, land, pause for a beat, then step off. That is a jump. Drop off a low box and spring straight back up the instant your feet touch the floor. That is a plyometric. From the outside the two look almost identical. Inside your legs they are completely different jobs, and that difference is the entire subject of this article.

The trick is not the jumping. It is the switch — how quickly you go from absorbing force to producing it. Get that switch fast enough and your tendons start giving you free energy, like a stretched elastic band snapping back. Take too long over it and the free energy leaks away as heat and you are just doing a slow squat with extra steps.

What follows explains what actually happens in your body during one of these reps, why the time your foot spends on the ground is the number that defines the whole method, how to judge whether a drill is hard or easy in a way that is actually useful, and how to build up to it without wrecking your knees. Everything comes back to one idea: plyometrics train how fast you can produce force, not how much force you can produce.

‌

Bounce, not jump

Every rep has three parts, and the middle one is the whole game. You go down, you switch, you go up. Sports science calls the switch the amortisation phase, which is a needlessly grand name for something that lasts a few hundredths of a second. Everything you are trying to train lives in that tiny window. The going down and the going up are just what happens either side of it.

Two things help you during the switch, and both have a short shelf life. When a muscle and tendon get stretched fast, the tendon stores energy the way a bow does when you pull the string, and your nervous system fires off a reflex that adds a bit of extra pull. Both are useful. Both fade fast. Hold the bottom position for even half a second and you have thrown most of it away — which is exactly why a pause turns a plyometric back into an ordinary jump.

Intensity has nothing to do with how tired you feel. This one catches almost everybody out. Hard, in this context, means how much force lands on your tissue in that instant of contact. Dropping off a tall box and rebounding is brutally intense even though it takes one second and leaves you breathing normally. Skipping for two minutes feels far worse and is far gentler. If you judge these drills by how much they make you puff, you will get the dosing exactly backwards.

Count landings, not sets. One foot strike is one ground contact, and contacts are the currency here. It is worth actually counting them, because the cost to your tendons and joints piles up much faster than your legs let on. Feeling fine at the end of a session says very little about how your knees will feel two days later.

Strength sets the ceiling; this stuff helps you reach it. Think of strength as the size of the engine and plyometrics as how quickly the throttle responds. A powerful engine with a sluggish throttle is slow. A snappy throttle on a tiny engine is still a tiny engine. You need both, and neither one is a substitute for the other.

You have to be able to land before you are allowed to bounce. That is not a formality, it is the entry requirement. If you cannot come down from a modest height and absorb it quietly and under control, adding a rebound on top just means the same messy landing happening faster and with more force. Landings first, always.

Tired legs cannot do this. The moment fatigue arrives, contact times stretch out, the bounce disappears, and you are grinding through reps that no longer train the thing you came for. So this work goes early in a session, while you are fresh, and a set ends the moment it starts to feel heavy rather than springy. Stopping early here is not laziness, it is the point.

The rest of the article goes into the detail: each of the three phases properly, how contact time separates fast from slow variations, real intensity rankings, landing progressions, and how to slot the work into a training week. Those sections are more technical, so read them when you want the mechanism rather than the map.

‌

Why the fast reversal matters

When a muscle and its tendon are stretched rapidly, two useful things happen at once. First, the tendon behaves like an elastic band and stores energy. Second, sensory receptors inside the muscle detect the speed of the stretch and trigger a reflex that increases muscle activation. If the muscle then shortens immediately, both contributions are added to the voluntary effort and the resulting output is greater than the muscle could produce from a standstill.

‌

The catch is that both contributions are perishable. Elastic energy stored in a tendon dissipates as heat within a fraction of a second, and the reflex contribution fades just as quickly (Komi, 2000). Pause at the bottom of the movement and you throw both away. This is why a countermovement jump, where you dip and immediately jump, is reliably higher than a squat jump started from a held position (Bobbert et al., 1996).

‌

The three phases of a plyometric actionA left to right chain showing the eccentric loading phase, the amortisation or transition phase, and the concentric output phase, with the amortisation phase highlighted as the critical variable.The three phases of a plyometric actionEccentricMuscle lengthens under load. Elastic energyis stored in tendon and the stretch reflexis triggered.AmortisationThe transition between lengthening andshortening. Measured in milliseconds.Energy leaks away as heat the longer itlasts.ConcentricMuscle shortens. Voluntary contraction plusrecovered elastic energy plus reflexcontribution produce the output.

Figure 3.1.1 — Every plyometric repetition passes through the same three phases. The middle phase, amortisation, is the one that separates a plyometric from an ordinary jump: The shorter it is, the more of the stored elastic energy survives to contribute to the push.

‌

The three phases in plain language

• Eccentric phase. The muscle lengthens while resisting. In a depth jump this is the moment your feet contact the ground and your ankles, knees and hips begin to bend. Force is high here, often several times bodyweight.
• Amortisation phase. The changeover from lengthening to shortening. Nothing appears to happen, which is why it is easy to ignore, but this is where the method succeeds or fails. Short amortisation preserves the stored energy; long amortisation wastes it.
• Concentric phase. The muscle shortens and the body accelerates. The output here is the sum of voluntary contraction, recovered elastic energy and the reflex contribution.

‌

Coaches often describe the goal as minimising time on the ground. That is a practical shorthand for keeping the amortisation phase short. It is also why plyometric coaching cues almost always emphasise speed off the ground rather than height achieved.

‌

What plyometrics are not

Plyometrics are not a conditioning method. A set of ten depth jumps should leave you barely breathing and completely fresh, because the goal is a small number of very high-quality efforts. If a plyometric session feels like a cardiovascular workout, it has been programmed as circuit training and will not produce the intended adaptation.

‌

They are also not a substitute for strength training (Requena & Newton, 2010). The relationship works the other way around: Strength raises the amount of force available, and plyometrics train the ability to express a large fraction of it in the very short time windows that sport allows. An athlete with a modest strength base will get some benefit from plyometrics but will run out of runway quickly.

‌

A useful rule of thumb: If you cannot control the landing, you are not ready to rebound from it. Landing competence is the gate through which all plyometric progression passes.

‌

The mechanisms in more detail

Elastic energy storage in the series elastic component

Muscle fibres themselves are poor springs. The elastic behaviour that plyometrics exploit comes mostly from the tendon and the connective tissue in series with the contractile fibres, collectively described as the series elastic component. When this tissue is stretched it stores energy in the same way a stretched spring does, and it returns a large proportion of that energy if the shortening follows quickly enough.

‌

The efficiency of this return depends heavily on tendon stiffness. A stiffer tendon transmits force more directly and returns stored energy faster, which is advantageous for short-contact activities such as sprinting and repeated hopping. A more compliant tendon stores more energy over a longer stretch, which suits movements with a longer, slower countermovement. This is one reason that different athletes respond differently to the same plyometric prescription.

‌

Tendon adapts, but on a slower timescale than muscle. Increases in tendon stiffness are typically observed over months rather than weeks, and they respond particularly well to heavy slow loading and to sustained isometric work, not only to fast plyometric loading. A complete programme usually contains both.

‌

The reflex contribution and its limits

Muscle spindles lie within the muscle and are sensitive to both the amount and the rate of stretch. A rapid stretch produces a burst of afferent activity that reaches the spinal cord and returns as increased motor drive to the same muscle. This is the stretch reflex, and it arrives fast enough to contribute to force during the concentric phase of a quick plyometric action.

‌

Alongside it, the Golgi tendon organ sits at the muscle-tendon junction and reports tension to the spinal cord through Ib afferents. Textbooks describe this as a protective brake that cuts motor drive once tension gets high, and describe plyometric training as turning that brake down. Neither half stands up well: Ib feedback is better understood as one input into task-dependent spinal and supraspinal control, its effect on motor output can be inhibitory or facilitatory depending on the task, the phase and the joint position, and there is no direct human evidence that training desensitises or withdraws a protective brake (Chalmers, 2002). It is more accurate to say that plyometric training improves neural drive and coordination during fast eccentric-to-concentric transitions than to attribute the change to a single mechanism.

‌

Because the reflex contribution depends on the rate of stretch, it is sensitive to how the movement is performed rather than to how much load is used. This is why technique and intent matter more in plyometrics than in most other training methods.

‌

Fast and slow stretch-shortening cycles

It is conventional to divide stretch-shortening cycle actions into fast and slow categories based on the duration of ground contact, with roughly 250 milliseconds used as the dividing line (Flanagan & Comyns, 2008). Sprinting, repeated hopping and short-contact bounding sit in the fast category. A countermovement jump, a change of direction from higher speed, and most jumping for maximum height sit in the slow category.

‌

The distinction matters because the two categories are trained by different exercises and transfer to different tasks. An athlete who needs to improve maximum vertical jump height is working mainly on slow stretch-shortening cycle qualities. A sprinter who needs to reduce ground contact time at top speed is working mainly on fast qualities. Training one does not automatically improve the other.

‌

• Fast stretch-shortening cycle (SSC). Ground contact under roughly 250 ms. Small joint excursions, stiff ankle behaviour, high reliance on tendon elasticity. Trained by pogo hops, ankle hops, short-contact hurdle hops, depth jumps and sprinting.
• Slow SSC. Ground contact above roughly 250 ms. Larger joint excursions, greater reliance on muscular contribution. Trained by countermovement jumps, box jumps, broad jumps and loaded jump variations.

‌

Measuring intensity and quality properly

The most common programming error in plyometrics is treating intensity as a subjective feeling. A more defensible approach is to recognise that intensity means the peak force the tissue must accept. Ground contacts from a greater height, on one leg, or with added load all raise peak force, regardless of how easy the exercise feels (Chu & Myer, 2013).

‌

Where measurement is available, the reactive strength index provides a practical objective measure. It is calculated by dividing jump height by ground contact time, so it rewards jumping high and leaving the ground quickly, which is exactly the quality the method aims to develop (Flanagan & Comyns, 2008). Tracking it across a training block reveals whether reactive ability is improving or whether accumulated fatigue is degrading it.

‌

Even without equipment, ground contact time can be judged usefully by ear. Consecutive contacts should sound short, light and rhythmic. When contacts become audibly heavier or the rhythm becomes uneven, the set has gone past the point where it is training the intended quality.

‌

Where plyometrics sit on the force-velocity curveA descending curve of force against velocity, with labelled regions for maximal strength at high force and low velocity, power in the middle, and speed and plyometrics at high velocity and lower force.Where plyometrics sit on the force-velocity curveForce-velocity relationshipLowModerateHighLowModerateHighMovement velocityForce producedMaximal strengthPowerSpeed and plyometrics

Figure 3.1.3 — Plyometrics occupy the high-velocity end of the force-velocity relationship. Heavy strength work builds the ceiling; plyometrics train the ability to express force in the very short time windows that sport actually allows.

‌

What plyometric training actually changes

Meta-analytic reviews of plyometric training consistently report improvements in vertical jump performance, with typical gains in the region of several centimetres over training blocks of six to ten weeks (Kellis et al., 2009). Improvements are also commonly reported in sprint performance over short distances, in change of direction ability, and in measures of reactive strength (Markovic & Mikulic, 2010).

‌

The adaptations underlying these changes are a mixture. There are neural changes, including improved motor unit recruitment and better timing of activation across the muscles crossing a joint. There are musculotendinous changes, including altered tendon stiffness and changes in muscle architecture. There are also coordination changes that are best described as skill: The athlete simply becomes better at performing the specific task.

‌

The practical implication of the skill component is that a substantial part of early improvement is task-specific (Markovic & Mikulic, 2010). An athlete who trains only double-leg vertical jumping will improve at double-leg vertical jumping more than at single-leg lateral bounding. Programmes should therefore include the movement directions and limb configurations that the sport actually demands.

‌

Programming plyometrics without breaking anyone

Plyometric programming is mostly about restraint. The method works with small doses of very high quality, and most of the problems that arise in practice come from doing too much, doing it when tired, or progressing intensity before the athlete has earned it.

‌

Sequencing intensity

Progression should follow tissue tolerance rather than the calendar. The ladder below is a workable default sequence, but movement between levels is governed by the readiness criteria that follow it, not by elapsed weeks.

‌

A plyometric intensity ladderFive stacked rows ordered from lowest to highest intensity, from landing drills through to depth jumps and single leg reactive work, showing how plyometric exercises are sequenced.A plyometric intensity ladder1. Landing and absorptionAltitude landings, snap-downs, drop landings to a stick. No rebound at all.2. Low-amplitude hops in placeAnkle hops, pogo hops, jump rope. Short contacts, small displacement.3. Jumps for height and distanceCountermovement jumps, box jumps, broad jumps. Landing is controlled, not rebounded.4. Repeated and reactive jumpsHurdle hops, repeated broad jumps, bounding. Consecutive contacts with short ground time.5. Shock and single-leg reactiveDepth jumps, depth drop to hurdle hop, single-leg depth jumps. Highest force, lowest volume.Lower forceHigher force

Figure 3.1.2 — Intensity in plyometrics is not about effort or fatigue, it is about the peak force the tissue must accept. Work upward only when the current level is landed quietly and under control.

‌

Readiness criteria before progressing plyometric intensityA table with progression stages as rows and readiness criteria as columns, showing what should be true before an athlete moves to the next level of plyometric intensity.Readiness criteria before progressing plyometric intensityLanding qualityVolume toleranceStrength baseLanding and absorptionLands quietly, holds position 2–3sNo next-day joint sorenessCan squat bodyweight with controlLow-amplitude hopsRhythmic, quiet, knee stays quietTolerates 60–100 contactsCalf and foot tolerate dailywalking loadJumps for height/distanceLands balanced, knees track overfeetTolerates 80–120 contactsSquat pattern loaded and painfreeRepeated and reactiveContact time stays short acrossrepsTolerates 100–140 contactsDemonstrable eccentric controlShock and single-legNo knee valgus, no secondary hopLow volume only, 30–60 contactsWell-established strength history

Figure 3.1.4 — Readiness is judged on movement quality, not on how long an athlete has been training. If any column fails, the athlete stays at the current level.

‌

Counting volume

Volume in plyometrics is counted in ground contacts. A set of five hurdle hops is five contacts per repetition sequence, and it accumulates quickly across an session. Typical guidance for a training session ranges from around 60 to 100 contacts for athletes new to the method, up to roughly 120 to 150 for well-trained athletes performing lower-intensity work, with high-intensity shock work kept substantially lower (Potach & Chu, 2016).

‌

These numbers are guidance rather than prescription. The more useful discipline is to record contacts, watch how the athlete responds over the following two days, and adjust. Tissue that is being loaded faster than it adapts usually announces itself as tendon soreness that appears the day after and lingers.

‌

Placing plyometrics in the session and the week

1. Warm up thoroughly, including some low-level hopping to prepare the ankle and foot.
2. Perform plyometric work early, after the warm-up and before heavy strength or conditioning work.
3. Keep rest between sets generous, typically one to three minutes, because the goal is a fresh nervous system rather than accumulated fatigue.
4. End each set on quality: When contact time lengthens or landings become noisy, the set is finished regardless of the number written on the programme.
5. Allow at least 48 hours between high-intensity plyometric sessions targeting the same tissue.

‌

Combining plyometrics with strength work

The two methods are complementary and the sequencing within a session usually favours placing plyometrics first, because they demand a fresh nervous system and are compromised by prior fatigue. An exception is deliberate contrast or complex training, where a heavy strength set is followed after a short rest by an explosive set in order to exploit post-activation potentiation. That approach can be effective but requires an established strength base and careful management of the rest interval.

‌

Across a training year, the usual pattern is to build a strength base first and then bias toward plyometric and speed work as competition approaches, while maintaining enough strength work to hold the ceiling in place.

‌

Sport applications

For basketball and volleyball, both fast and slow stretch-shortening cycle qualities matter. Repeated jumping within a rally is a fast quality; a maximal block or approach jump is closer to a slow quality. Programmes usually need both, with the added requirement of single-leg competence because so much jumping in these sports is off one leg.

‌

For sprinting and field sports, the emphasis shifts firmly toward fast stretch-shortening cycle work and toward horizontal force production. Ankle hops, short-contact hurdle hops, bounding and sprint-specific plyometrics carry more relevance than maximal vertical jumping.

‌

For combat sports, plyometric qualities appear in the legs for level changes and footwork, and in the trunk and upper body for striking. Medicine ball throws and rotational work sit alongside lower-body jumping.

‌

For older athletes and general populations, the method still applies but the entry point moves earlier in the ladder. Low-amplitude hopping and controlled landings deliver meaningful benefit for bone density, tendon health and the ability to recover balance, without the tissue cost of shock work.

‌

Common mistakes

• Using plyometrics as conditioning. Long sets performed to fatigue turn a power method into a circuit. Contact time lengthens, quality collapses, and the specific adaptation is lost while the injury risk rises.
• Treating jump height as the only outcome. A high jump with a long ground contact is not a good plyometric repetition. Track height and contact time together, or at minimum listen for short, quiet contacts.
• Progressing box height instead of quality. Raising the box is the most visible way to progress and often the least useful. If contact time lengthens as the box rises, the increase has made the exercise worse.
• Skipping the landing phase. Athletes who cannot absorb and hold a landing are not ready to rebound from one. Time spent on altitude landings and snap-downs is not wasted preparation, it is the foundation.
• Adding plyometrics at the end of a hard session. The method depends on a fresh nervous system. Performed on tired legs it trains a slower, less reactive version of the pattern.
• Ignoring the single-leg case. Most sporting jumps and nearly all running contacts are single-leg. A programme built entirely on double-leg jumping leaves an obvious gap.
• Counting sets instead of contacts. Contacts are the unit of tissue loading. Counting sets consistently understates the true dose, particularly for repeated-jump exercises.

‌

Coaching cues

• Off the ground fast, not up high
• Land quiet, and hold it
• Ankles stiff, knees quiet
• Think of the floor as hot
• Same rhythm every contact
• Stop the set when the sound changes
• Tall through the hips

‌

FAQs

How often should I do plyometrics?

For most athletes, two sessions per week of dedicated plyometric work is sufficient, with at least 48 hours between sessions that load the same tissue in the same way. Low-intensity hopping and landing work can be performed more frequently, often daily as part of a warm-up, because the tissue cost is much lower.

‌

Do I need to be strong before starting plyometrics?

You need enough strength to control landings, which is a lower bar than the frequently quoted requirement of squatting one and a half times bodyweight. That figure is a reasonable guideline for high-intensity shock work such as depth jumps, but it is not a prerequisite for low-amplitude hopping or landing drills. A more useful test is whether the athlete can land a drop from a low box quietly and hold the position.

‌

Are plyometrics safe for young athletes?

Appropriately prescribed plyometric training is generally considered safe for children and adolescents, and it is commonly included in youth athletic development and injury-prevention programmes (Lloyd et al., 2015). The requirements are competent supervision, an emphasis on landing mechanics, modest volumes, and progression based on movement quality. The risk comes from excessive volume and poor technique rather than from the method itself.

‌

How long before I see results?

Measurable improvements in jump performance are commonly reported over training blocks of six to ten weeks. Some early improvement appears sooner and is largely coordination: The athlete becomes better at the specific task. Changes in tendon properties develop more slowly, over months.

‌

Should I feel sore after plyometrics?

Mild muscular soreness after an unfamiliar session is normal. Tendon soreness, particularly around the Achilles or patellar tendon, that appears the following day and persists is a signal that volume or intensity has outpaced adaptation. Reduce contacts, return to a lower level on the ladder, and rebuild more gradually.

‌

Is jumping rope a plyometric exercise?

Yes, in the sense that it involves rapid stretch-shortening cycle actions at the ankle with very short ground contacts. It sits low on the intensity ladder, which makes it a useful preparatory and low-level option, but the small joint excursions mean it will not develop high-force reactive qualities on its own.

‌

Recommended videos

Each video below was chosen because it covers a specific part of this article in more depth than text alone allows.

‌

‌

‌

‌

‌

‌

‌

‌

‌

‌

Related reading on FitXplor

• 3.2 The Stretch-Shortening Cycle
• 3.3 Landing Mechanics and Force Absorption
• 3.8 Jump Training and Vertical Power
• 3.9 Reactive Strength and Elastic Qualities

‌

References

Komi, P. V. (2000). Stretch-shortening cycle: a powerful model to study normal and fatigued muscle. Journal of Biomechanics, 33(10), 1197–1206.

Bobbert, M. F., Gerritsen, K. G., Litjens, M. C., & Van Soest, A. J. (1996). Why is countermovement jump height greater than squat jump height? Medicine & Science in Sports & Exercise, 28(11), 1402–1412.

Markovic, G., & Mikulic, P. (2010). Neuro-musculoskeletal and performance adaptations to lower-extremity plyometric training. Sports Medicine, 40(10), 859–895.

Sáez-Sáez de Villarreal, E., Requena, B., & Newton, R. U. (2010). Does plyometric training improve strength performance? A meta-analysis. Journal of Science and Medicine in Sport, 13(5), 513–522.

Sáez-Sáez de Villarreal, E., Kellis, E., Kraemer, W. J., & Izquierdo, M. (2009). Determining variables of plyometric training for improving vertical jump height performance: a meta-analysis. Journal of Strength and Conditioning Research, 23(2), 495–506.

Flanagan, E. P., & Comyns, T. M. (2008). The use of contact time and the reactive strength index to optimize fast stretch-shortening cycle training. Strength and Conditioning Journal, 30(5), 32–38.

Potach, D. H., & Chu, D. A. (2016). Program design and technique for plyometric training. In G. Haff & N. T. Triplett (Eds.), Essentials of Strength Training and Conditioning (4th ed.). Human Kinetics.

Chu, D. A., & Myer, G. D. (2013). Plyometrics. Human Kinetics.

Hewett, T. E., Myer, G. D., Ford, K. R., et al. (2005). Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes. American Journal of Sports Medicine, 33(4), 492–501.

Lloyd, R. S., Oliver, J. L., Faigenbaum, A. D., et al. (2015). Long-term athletic development, part 1: a pathway for all youth. Journal of Strength and Conditioning Research, 29(5), 1439–1450.

Chalmers, G. (2002). Strength training: Do Golgi tendon organs really inhibit muscle activity at high force levels to save muscles from injury, and adapt with strength training? Sports Biomechanics, 1(2), 239–249. Read on Europe PMC