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  • Writer's pictureJo Clubb

Jump Testing with Force Plates Explained

Updated: May 24

In sports science, jump testing has become a cornerstone of athlete performance assessment. Across team sports, understanding the mechanics and outputs of various jump tests can provide invaluable insights into an athlete's muscle power and neuromuscular function. This post will delve into the basics of jump testing, focusing on popular tests such as the countermovement jump, squat jump, and drop jump, and explain how force plates enhance the depth of information from these assessments.


Why measure jumps?


Jump testing has become a common method for assessing athletic capacities, because it offers a straightforward method, time efficiency, and familiarity in the triple extension movement demand for most athletes. While jumping is obviously crucial in sports like basketball and volleyball, its measurement is valuable across all sporting disciplines, as the tests can reveal different aspects of an athlete's physical condition and help track progress in physical capabilities.


Force plates, such as VALD's ForceDecks, provide detailed insights into jump performance by measuring highly precise force-time data, from which measures such as velocity, acceleration, and power can be derived. They enable not only the assessment of the overall jump outcome, but also in understanding the strategies an athlete has used to achieve those outcomes. For more on how force plates work, have a read of our force plate guide.



In the following, let's take a look into three of the most popular jump tests used in applied practice; the countermovement jump (CMJ), squat jump (SJ), and drop jump (DJ), along with key points for measuring each.


Countermovement Jump (CMJ)


The CMJ is widely implemented, owing to its natural movement pattern for

athletes and the lower technical demands compared to other

jump tests, such as a drop jump (Bishop et al., 2023). It involves a downward movement followed by an explosive upward jump.


Key Points

  • Arm Swing: Deciding whether to allow arm swing is crucial as it can influence jump height by adding upper body momentum. With arm swing is referred to as an Abalakov jump test whereas, a CMJ is offered conducted without for greater test control.

  • Body Weight Measurement: Ensuring a stable pre-jump phase on the force plate is essential for accurate data.

  • Force-Time Curve: The force-time curve for CMJ (shown in the figure below by VALD Performance) includes phases like unweighting, braking, and propelling, which provide insights into the athlete's performance dynamics.

A CMJ forcetime curve is shown in grey, with annotations displaying key landmarks
Key Landmarks in a Countermovement Jump (courtesy of VALD)

Squat Jump (SJ)


The squat jump starts from a static squat position and involves only the concentric phase of the jump, eliminating the eccentric demand during the downward phase of a CMJ. This makes it useful for assessing concentric force production alone.


Key Points

  • Concentric Focus: By removing the eccentric phase, the SJ highlights the athlete’s ability to generate force without the benefit of the stretch shortening cycle.

  • Visual and Data Assessment: Ensure the athlete does not dip before jumping, which can be checked both visually by watching the athlete and via the force-time curve.


Eccentric Utilisation Ratio (EUR)

Combining data from CMJ and SJ, the eccentric utilisation ratio (EUR) assesses how effectively an athlete uses their stretch-shortening cycle (SSC). An EUR above 1.1 indicates good utilisation, as it represents 10% greater performance with the SSC.


For those at 1.1 and above, a mixed program incorporating both strength and ballistic training is recommended. However, lower than 1.0 suggests a focus on plyometric training to enhance the athlete's ability to utilise their SSC. However, just as we discussed with the Dynamic Strength Index (DSI), any simplified ratio has its limitation and such training decisions should be made from a mixture of information.


Drop Jump (DJ)


The drop jump tests an athlete’s reactive strength by measuring their ability to quickly transition from the eccentric (landing) phase to the concentric (take-off) phase. This test is performed from a height, and the goal is to minimise ground contact time while maximising jump height. Whereas, the CMJ assesses the slow SSC, the DJ tests the fast SSC.


Key Points

  • Reactive Strength Index (RSI): Calculated by the ratio of jump height to contact time, RSI provides insights into an athlete’s reactive strength.

  • Plyometric Profiling: Testing DJ across a range of drop heights allows the plotting of RSI and a plyometric profile. Eamonn Flanagan has recommended if RSI decreases (or ground contact times >250ms are observed) with increasing height, the individual's reactive strength capacities are not sufficient.

  • Safety and Technique: Given its greater physical and technical demands, ensure athletes are capable of performing the DJ safely, especially those recovering from injuries, and a suitable box height is used.


FAQs on Jump Testing with Force Plates


What is jump testing?

Jump testing involves assessing various jumps to measure an athlete's muscle power and neuromuscular function. Understanding the requirements and mechanics of different jump types, enables practitioners to determine the most suitable test(s) to use with their athletes.


What is a countermovement jump (CMJ)?

A CMJ involves a downward movement followed by an explosive jump, providing a simple method for testing lower body power and force capabilities.


How does a squat jump (SJ) differ from a CMJ?

The SJ starts from a static squat, focusing on concentric muscle power by eliminating the pre-jump downward movement (the eccentric phase) seen in CMJ.


What is the eccentric utilisation ratio (EUR)?

EUR compares performance metrics, such as jump height or power, from CMJ and SJ to evaluate how effectively an athlete uses the stretch-shortening cycle. If the EUR is below 1.1, focussed plyometric training may be warranted to improve their SSC capability.


What is a drop jump?

A DJ involves jumping off a height and immediately rebounding, testing the athlete's reactive strength and ability to transition quickly from landing to take-off.

(RSIS


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The logo for the sports technology company, VALD Performance, in orange on a white background. The logo is an outline of a Viking style helmet, with the words VALD PERFORMANCE capitalised underneath.

This article is support by VALD Performance. For more information, about their technology, visit their website.

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