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Breaking Down To Jump Up: Understanding Plyometrics With Force Plates

cmj force plate Jan 24, 2024

In the world of athletic development, speed and jumping performance are often key qualities that determine performance. Plyometric exercises, which are based on the science of the stretch-shortening cycle, play a key role in improving athletic performance and serve as important criteria for returning to sports after injury. These exercises use the body's natural elastic properties to create explosive movements, offering a dynamic approach to training. A solid grasp of plyometrics enables professionals to design programs that significantly boost physical capabilities, leading to improved health and performance outcomes for athletes and individuals alike.

In this article we will discuss how the use of smart force plates like AxIT Stomp-IT can be used to break down and understand the key elements of jumping.

  1. What assessments can be employed?
  2. Which metrics to look at?
  3. Basic strategies for interventions.

Understanding the Stretch-Shortening Cycle (SSC)

The SSC is like the body's rubber band. It involves a three-step process where a musculotendinous unit is rapidly stretched, storing elastic energy as it reaches maximal length, and subsequently recoiling and shortening rapidly to generate an action such as jumping into the air.

By breaking down these phases into appropriate Force Plate tests using Stomp-IT, practitioners can better determine where the focus is needed for the athletes they work with.

Eccentric Absorption.

As described, the initial phase focuses on the eccentric component of movements, often referred to as the "force absorption" phase. This entails rapidly transitioning joints in the lower body from an extended to a flexed position. An example assessment and training exercise for eccentric absorption is the "tall-to-short" or "drop squat." This test can be created with a Custom Test variation of your standard squat assessment in AxITs software.

When evaluating results, metrics related to eccentric motions are key indicators. This phase sets the foundation for landing – much like learning to land before taking flight, this is an important first step.

The most important metric here is Peak Force. This is the maximum eccentric force generated throughout the movement; progression is indicated by increased peak force as the athlete becomes more adept at the action.

For athletes returning from injury, often the symmetry of the affected and unaffected limbs is most important. By establishing a target value, often around 10-15% asymmetry, clear criteria for advancement can be set.

Interventions at this stage might focus on general strength, isometrics and basic technical drills.

Concentric Development.

Concentric development targets the muscle-shortening facet of the jump and SSC. Immediately following the eccentric and energy storage phase of the jump, muscles rapidly contract as joints transition from flexion to extension. Concentric development is assessed using a Squat Jump test.

The Squat Jump assessment zeroes in on the concentric phase, which starts exactly where the drop squat assessment ends – at the bottom position of the squat. By pausing in this position before performing the jump action we remove the elastic effect of the SSC and allow AxIT to measure concentric force production.

Key metrics for concentric force development are:

  • Jump Height: Peak vertical displacement post take-off, indicative of enhanced concentric power.
  • Take Off Velocity: Maximal upward speed, improving this value indicates enhanced speed with increased power.
  • RFD: Rate of force development during take-off; reflects acceleration capability and improves with targeted power-focused training.

Interventions at this stage may focus on concentric variations including dead starts, super slow eccentric to concentric tempo reps, pause reps and fast concentric efforts.


Jump tests combine the two movements tested above. It involves executing the eccentric and concentric components consecutively, marking the introduction of the stretch-shortening cycle. In a normal jump, the tissue lengthening to shortening occurs during a deeper, slower contact time (>0.25 secs) resulting in predominantly hip and knee joint movement from flexion to extension, and can be assessed using the Countermovement Jump (CMJ) test in the AxIT software.

CMJ metrics provide a comprehensive view of how athletes navigate jumping actions. Key metrics include:

  • Jump Height: Reflecting improved SSC utilization and elastic properties as power increases.
  • Eccentric Braking Impulse: Reflects proficiency in achieving greater momentum during eccentric phases.
  • Concentric Propulsion Impulse: Modifying exercise tempo for greater momentum in the take off phase can enhance performance.

Interventions at this stage may focus on building greater eccentric capacity such as controlling the depth of the eccentric phase, using eccentric overload with external load such as weights, flywheels or resistant bands.

Repeat Jumps.

Repeat jumps advance Jump Integration by introducing frequency. This involves consecutively performing bouts of the SSC typically under a short contact time of <0.25 seconds, resulting in greater fast stretch and a more ankle-dominant focus. The 10/5 Repeat Jump/Hop Test evaluates this by observing performance changes over time, particularly as the athlete looks to optimize their efficiency in repeat jump performance.

Noteworthy metrics include:

  • Reactive Strength Index (RSI): Average relationship between ground contact and Jump Height
  • Ground Contact Time (GCT): Ground time between jumps, the shorter this time, typically the more elastic the jump. May help to indicate if this should be a training focus.

Interventions at this stage will often focus building the capacity of the shank tissues as well as improving technical ability.

Drop Jump.

Drop Jumps (DJ) intensify SSC stimulus by creating more eccentric load due to the drop down height. This elevates force demand for transitioning from lengthening to shortening, rendering the plyometric action more challenging and making it a more advanced assessment of plyometric capacity and reactive strength.

Relevant metrics include:

  • RSI: Looks at the relationship between an outcome variable (height) vs strategy variable (contact time). Where is the optimum relationship
  • Ground Contact Time: Time on the ground, driven by cues and the same training factors as Repeat Jump/Hop Tests.
  • Jump Height: The ultimate reflection of jump performance.

Interventions at this stage may focus on using RSI to help determine optimal drop height for training ie which height does the athlete perform best? Typically the greater the stretch load tolerance, the greater the height the athlete can train at for drop jump, and depth jump exercises.


Breaking down the details of plyometric exercises in the mentioned stages gives professionals a clear view of their clients' physical strengths and areas that need improvement. This understanding not only helps create personalized training plans but also sets a strong base for meeting specific criteria when working with athletes aiming for a successful comeback in sports. By using various tests, professionals can identify imbalances, find areas that need improvement, and recommend specific exercises to connect the gap between rehabilitation, a secure return to competition, and achieving top performance.

Want to learn more?

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