Hundreds of professional sporting organizations are now using force plates due to their affordability and feasibility. Testing takes less than a minute to perform, provides rapid feedback, and produces objective data with high reliability when used properly.
Unfortunately, many people overcomplicate this tool or find the complexity daunting. This post serves as an actionable resource for those wanting to advance their evaluation of neuromuscular performance using force platforms. It’s no more or less than the musings of one avid force plate user.
While I’ve been incredibly fortunate to have extensive guidance in this area from the very best, including the outstanding mentorship of Dr. Daniel Cohen and further guidance from the likes of Dr. Phil Graham-Smith, Drew Cooper, and Daniel Martinez, any errors below are mine. Academic and detailed texts exist in the literature and more are on the way. I mention these at the end of this post.
A Word on Force Plates and Professional Growth
Many strength coaches are either into using technology or not. Hopefully, most are realizing that one way or another, technology is now a part of our jobs. Many have begun to use force plates and found themselves overwhelmed with the information and options or ended up overcomplicating matters and confusing athletes and staff—sometimes making their lives more difficult than necessary.
Throughout this post, I refer to preferred minimalist approaches. And while I offer significant detail, the vast majority of force plate users will benefit most from the information on protocols, setup, logistics, and data use—not complexity, test selection, or niche variables. Of course, this comes back to the concept of simplicity done very well, which is overused but still true!
In the day-to-day operations of sports science, we often seek answers to the following questions:
- What and how much did the athlete do. How hard did they work? What was the load?
- How did they respond to the load? What is their current status and readiness?
- How normal is the above, and if not, what are the necessary changes to the next prescribed load?
The first two questions have an important dovetailing dynamic that could use more attention, while the third question is a matter of systems engineering, analytics resourcing, and individual intelligence.
Given that leading sports science professionals openly admit that as a field, we are poor at assessing load, why are we not focusing more on response to load? After all, it matters less what has caused stress than the awareness and accommodation of the stress itself.
Understanding response to recent load is perhaps more valuable than information on the amount of the load, says @CoolHandJakeGS. #forceplates Share on XPut another way, playing and running more than usual in last night’s game is not functionally different from a poor night’s sleep regarding today’s decisions. This detail and differentiation are useful, but we aren’t there yet. If we all agree that each day we are tasked with communicating to stakeholders the readiness of each athlete and our professional advice on their management, it’s fair to assume that clear and detailed understanding of athlete status—including their response to recent load—is significantly more valuable than information on the amount of the load.
Enter force plates.
Background: Technology, History, and Biomechanics
Force platforms, also called force plates, are (typically metal) surfaces upon which athletes can perform a variety of movements. The plates are under-rigged by strain gauges or load cells that measure force and time at high-frequencies.
Jumping, landing, and isometric movements typically are assessed through the derivations of impulse to produce velocity, momentum, and flight outputs and from these measures, power, acceleration and displacement. Assessments of the forces applied to and by objects are categorized as kinetic. Kinematics (or the motion of objects), on the other hand, require more (and much more expensive) technology and specialized biomechanical and statistical analyses.
Until recently, force plates often featured significant limitations on their feasibility in daily sporting environments:
- Single, large, and very heavy platforms prevent limb-specific (and therefore asymmetry) outputs
- Portability issues
- Labor-intensive data extraction requiring both specialized computing skills and prohibitive amounts of time
- Software limitations
Currently, there are multiple available technologies providing instantaneous feedback to users with automatic variable calculation in the dozens, with often over one hundred variables available to compare and contrast athletes and inter-individual variations over time. Of important note is that this article will focus on applications of uni-axial force platforms, measuring only vertical displacements; tri-axial force platforms providing insight on horizontal displacement and thus opening great possibilities for dynamic multidirectional assessments are of outstanding value in cases where an organization has the resources, time, buy-in, standardization of testing, and specialized skillsets available to evaluate the resultant data. However, as the vast majority of practitioners and organizations either do not have such resources and/or have not yet integrated “simple” vertical assessments into their programs for the greatest possible return of value, I will focus on those such applications here.
Common Procedures: Types of Tests and Typical Prescriptions
We categorize tests on uniaxial force plates as jump-landing (or jumps), landing, or isometric movements. With rare exceptions, these evaluations are designed explicitly for standardized neuromuscular evaluations. This does not mean generic, nor without intended or possible application and transferability to sporting qualities. It means that the movements are not sport-specific and instead provide neuromuscular information from which we can derive sport-specific insights.
Force plate movement tests are not sport-specific; they provide neuromuscular information from which we can draw sport-specific insights. Share on XAn example is a sport where a technical coach perceives an athlete has a weakness with change-of-direction ability. When this happens, the physical preparation staff executes an intervention and examines pre- and post-measures of rates of force development in the eccentric phase of a countermovement jump. The staff uses this information to assess an objective marker of outputs representing the qualities necessary to execute the key movement skills.
Common Tests
In applied settings, the two most common tests performed are the double-leg countermovement jump (CMJ) and the isometric mid-thigh pull (IMTP). Each has variations, including a single-leg CMJ (SLCMJ) and the use of either a squat rack (IsoSquat) or parallel bars for the isometric pull. I encourage you to consider your population and facility logistics to decide the appropriate application.
The next most common tests are the squat jump (SJ) and drop jump (DJ). The SJ is excellent for examining isolated concentric qualities—jumping ability in the absence of an elastic component and countermovement.
Shot-put throwers, football linemen, rugby forwards, and ice-skaters probably all benefit more from regular SJ testing than other athletes, but it has its place in initial profiling and intermittent monitoring for any athlete. For example, quarterly or at each training-cycle changeover period.
Comparing SJ and CMJ outputs, such as jump height or peak power, provides context on eccentric and concentric qualities (sometimes called the eccentric utilization ratio). Output comparisons also provide a nice second layer of jump analysis that examines training adaptations or retention of qualities over periods of time, such as in-season.
The DJ is a very interesting test. For many practitioners, it’s the go-to test because it’s the method through which we can derive the most information—contact time as well as flight time—from jump mats and similar technologies.
I’m not a huge fan, however. Cases where athletes drop jump reliably are far too rare, and athlete aversion to the impactful movement is far too common. The test does help examine how an athlete lands on the ground and their ability to turn around and leave the ground as quickly as possible. But the movement is far less idiot-proof (easy to teach, hard to mess up à clean data) than CMJ.
The drop jump has a place in profiling and intermittent testing, but it has limited reliability and athletes are especially averse to it when sore, says @CoolHandJakeGS. Share on XAlso, athletes can use technical strategies that result in false-positive performances. Or they can feel far less coordinated than they do with similar sporting skills, which creates false-negative information. DJ has its place in profiling and intermittent testing, but for me, it’s not sufficiently valuable as a regular testing method.
Another common and essential jump test is the land-and-hold (LAH). LAH is a profiling and intermittent monitoring tool that’s criminally underrated. While we can learn much information from the landing of the CMJ, we derive more specific information and deliberate context from an isolated landing. I expect future research will demonstrate its use for lower body injury screening and rehabilitation. I imagine this as a centerpiece for diving, gymnastics, throwers, and aerial skiers.
The land-and-hold jump test is my dark horse pick for the top three must-do tests in any setting, says @CoolHandJakeGS. #forceplates Share on XPerformed single- or double-leg, the LAH is my dark horse pick for a top three must-do tests in nearly any setting. Credit to Will Morgan (Australia Winter Sports) and Phil Graham-Smith for pointing me toward this one and up-skilling me on it.
Finally, position-specific isometric tests have become quite popular recently, with a range of variations offered in the literature and current practices. Common favorites are the calf, hamstring/posterior chain, and shoulder tests.
Position-specific isometric tests are very useful, and demand for upper-body tests will grow as throwing and racquet sports modernize. Share on XI’ve used all three in track and field and found them to be very useful. The supine single-leg posterior chain showed the strongest correlation to anything we measured to 60m and 100m sprinting performance in our Florida State sprinters during the 2017-18 season. While traditionally force plate tests have looked at lower body or total body movements, the demand for upper-body specific tests will continue to grow as throwing and racquet sports modernize (Ashworth 2018).
When to Administer Tests
For ideal best practice in any running-based or field and court sport, I suggest administering all of the above tests at the start of the season (and both start and end of preseason, if feasible). Administer the LAH, SL-CMJ, secondary Isos, and SJ tests monthly or at the turn of each training phase, and the CMJ + IMTP (or variation) or LAH as often as possible, preferably >3x/wk.
Test Administration and Cueing
As with any data collection, standardization and ecological validity are extremely important. One common fallacy when discussing CMJ eccentric variables is that they are not reliable. This is a byproduct of many studies that did not include cueing toward maximal velocity-effort.
When administering a CMJ, I cue the athlete to “be explosive and jump as high and as fast as you can!” If the athlete jumps as fast as they can, jump height will be true and, therefore, sensitive—reliable data is sensitive data.
Eccentric variables vary far more than concentric variables for the following reason: athletes are highly capable of altering jump strategy—often subconsciously or unintentionally—to take more time than typical for their countermovement (eccentric phase) to produce normal jump outputs. A classic example of a fatigued athlete is one who takes 100-200ms more than normal for the eccentric duration and yet produces a completely normal jump height. This is a common and brilliantly useful situation that practitioners should be looking for when administering CMJs.
When an athlete is cued to jump explosively and as fast as they can (often a second time after a slow first jump) during their attempts to jump quickly, their jump height may drop off, revealing fatigue. Conversely, a fresh athlete often displays reduced eccentric duration more than they will increased jump height or peak power.
With the IMTP & IsoSquat tests, and really any isometric test, pay attention to the athlete’s stability before the movement. The cueing depends on whether you’re interested in the rate of force development (RFD) or only peak force measures. Many practitioners do 1-3 reps of each, first cueing to ease into a true max and then instructing an explosive and fast pull.
Outputs: Variables and Meaningful Data
Force plate data is best examined through a lens zooming in and out. Many variables are useful to watch when profiling and screening athletes and when looking at long term trends. More acute and ongoing observations, however, are better narrowed to a handful of metrics known to be reliable (and therefore sensitive) and pertinent.
Where machine learning techniques are feasible, examining raw data or a large menu of variables can be beneficial. During week to week testing of the rhythms of a season, 3-6 variables from the CMJ are often sufficient to provide actionable monitoring information within healthy populations. The IMTP/IsoSquat, SJ, DJ, and LAH provide only a few variables that I’ll detail at the end of this section while the rest will focus on CMJ outputs.
Although there is always a place for loading up all of a players’ time-course data and examining their trends, I find it useful to break down typical “data views” to one of the following contextual purposes (each of which I examine more fully in the following sections):
Profiling and Screening: Initial, healthy baseline data to compare and contrast athletes within and between groups, evaluate their condition at the end of the offseason/start of the preseason, and filter for potential high-risk individuals.
Intermittent Monitoring: Monthly, quarterly, or at intervals representing the start or end of training and competitive phases specific to intended adaptations of physical statuses. Ideal for examining training effects and retention of qualities during competitive and high volume or low rest periods.
Load-Response Monitoring (LRM): As frequent as possible, with contextual accommodations for the acute and heteroscedastic nature of single data points. Match Day +2 is a typical LRM examination, comparing athlete data to their normal MD+2 as well as MD or MD- data. Discovering how an athlete typically enters a loaded period and how they respond to loads can be hugely beneficial for athlete management.
Rehabilitation: When an athlete is injured and in the return-to-perform (RTP) process, what we examine, how we examine it, and which tests we perform may be quite unique.
Profiling, Screening, and Intermittent Monitoring
In my experience, the variables of particular note in profiling, screening, intermittent monitoring, and long term athletic development (LTAD) (year to year) are often the same:
Jump Height. While we should not ignore this variable, we best treat it as a contextual placeholder representing overall athleticism and should not provoke reactions from day-to-day variation nor false negatives where stable. Mechanical and jump strategy variables described below are more sensitive.
Concentric Impulse and Eccentric Deceleration Impulse. These are phase-specific representations of force outputs. Deceleration, typically dependent on software applications, represents the eccentric phase minus unloading. Impulses are rate-vectors reported as Newton-Seconds (Ns). Impulse is the amount of force applied within the time taken. We can visualize it as the area under the curve/slope on a force-time trace. These (especially concentric) are closely related to jump height and are fairly stable, yet can evolve significantly with training effects and training age.
RSImod. Probably the ultimate catch-all jump performance metric that is also synonymous (though calculated slightly differently) with Flight Time:Contraction Time, RSImod encompasses how high and how fast. Anecdotally, RSI may continue evolving across training age after jump height plateaus, and there may be individual athletes who jump through the roof compared to those who jump very high and do so very fast!
Peak Power (relative and absolute). A mixed variable because explaining what exactly power is can be extremely ambiguous. Power is another interesting variable that provides isolated comparisons and, in contrast to jump height and RSI, can encompass body mass as a factor.
Load-Response Monitoring
For load-response monitoring, RSI can remain with the following sensitive variables added.
Eccentric Duration (ED). My favorite variable for monitoring readiness, or fatigue and freshness. ED will vary widely with jump strategy and mechanics provided we cue the athletes to consistently jump as fast as they can (or explosively). Transient or acute changes in RSImod likely will be reflected in ED, with athletes under fatigue or with otherwise impaired neuromuscular status demonstrating increased (elongated) ED. Individual sport athletes, when tapered or brought to peak for performances, can display reduced (shortened) ED.
Eccentric Deceleration RFD (EDRFD). Another favorite variable, this will wax and wane with ED, yet can represent quite different qualities. Stiffness is a misused term and concept, and this post will not cover spring-mass models. For me, EDRFD nicely represents an athlete’s bounce. If it’s poor, their ACL risk is possibly elevated (before considering asymmetries and a host of other factors). If it’s great, the athlete likely possesses a strong change-of-direction ability.
Concentric Impulse @ 100ms (Con-Imp100) (or another time constraint). Whereas total impulse answers the question of “how much force was applied in the time it took to complete the jump phase” (concentric, eccentric, etc.), Con-Imp100 informs how much force the athlete applied in the first 100ms of the concentric phase.
Concentric Rate of Power Development (Con-RPD). Cormie identified this in 2008 as a useful variable, essentially representing acceleration, using watts per second. Visualized as the slope of the power curve on a kinetics graph, RPD correlated with acceleration in collegiate sprinters in unpublished data. Sprinters who had higher RPD were consistently ahead at the 5m and 10m mark in races. RPD can be weight (/kg) or time (e.g., @50ms) constrained for more granular analysis.
Rehabilitation
Rehabilitation features its own set of contextual factors. First, great consideration—and the influence of medical staff—must be taken as to when we can integrate certain tests safely as well as at what stage certain variables become relevant. For example, bilateral CMJs reasonably may be integrated during lower body RTP far earlier than SL, though both are very useful and healthy baseline data is essential where feasible.
Further, practitioners will notice that eccentric peak velocity (Cohen, Aspetar in Press) may take a while to return to near healthy standards even when the rehabilitating athlete can perform jumps. Often asymmetries “disappear” early in the RTP process because athletes are not yet moving quickly enough to manifest intra-limb differences in meaningful magnitudes.
In any case, asymmetries and jump strategy or mechanical variables are likely to be a focus of RTP monitoring. While output variables such as jump height and total impulse may return to healthy baselines relatively quickly, EDRFD and its asymmetries, time-constrained impulses, and landing asymmetries often take far longer to revert to healthy norms in rehabilitating athletes.
Variables From Movements Other than the Countermovement Jump
Drop Jump. The DJ is typically integrated for contextual RSI information, though looking at contact time on its own has value, as does asymmetries.
Squat Jump. In the SJ, jump height is often the only metric used for comparison with CMJ-JH as a concentric utilization ratio, which essentially compares how much jump height ability the countermovement produces—how much force and velocity an athlete produces without an eccentric phase. We can also examine CMJ-parallel metrics from the concentric phase, including impulse, peak power, and RPD.
Land-and-Hold. The LAH typically provides only three metrics, all of which have contextual value. Time to stabilization (TTS) represents the duration between the instant of landing and the moment in which the weight (represented by force) detected by the plate stabilizes to within a set range, depending on the technology. Peak landing force refers to how stiffly or softly the athlete lands on the plates, which is relevant if we cue the athlete one way or the other. Asymmetry between limb-specific peak force is very interesting and can be a key marker during lower body injury rehabilitation. With that in mind, many practitioners choose to favor single-leg LAH and compare both TTS and peak landing forces between limbs once the athlete is cleared to do so.
Isometrics. With IMTP and other isometrics, variables can become quite nuanced with the right population. Stone’s recent 25-year review is a fantastic read on the topic. Most often, two metrics receive attention: peak force and RFD. Examining both, depending on cueing, is useful (see test administration section).
Looking Ahead: Future Research, Evolving Applications, and New Technology
New software capabilities will include auto-detection and analysis of traditional resistance training movements, such as squats and cleans, as well as more advanced force-time curve visualizations like waveform analyses. The research will begin to assess which variables may relate more closely to transient versus residual and chronic fatigue, as well as those which relate to more specific sport skills such as on-field speed.
While some inroads have been made in these areas already, much of this article’s content relies heavily on word-of-mouth best practice while the literature lags behind, as in any applied science.
Like most sports science information, there is work to be done to establish standards and benchmarks for different populations and variables. As each athlete and scenario is different, the question of “what is a good score” remains intentionally unanswered in many cases. The more data we can share, the more informed we’ll be, and the better technologies will be used.
Summary
Force plates are an extremely useful objective tool we can use to assess and monitor athletes, in particular their responses to load. Accordingly, force plates provide a very significant advantage over more limited jump-assessment technologies. I encourage you to use a broad range of tests in profiling and screening and intermittent monitoring and do very regular monitoring with CMJ (and, where feasible, IMPT/IsoSquat and LAH) over less frequent monitoring with more tests.
As with any sports science practices, data value and practice efficacy are directly affected by establishing meaningful changes and signal-to-noise balances, while minimizing report outputs and excessive data use as well as maximizing efficiency and actionable information streams.
Regardless of how well established a load monitoring system may be in a given environment, load management cannot be truly effective without a strong integration of load-response evaluations. Force plates provide an outstanding tool with which to do this.
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Further Reading and References
An upcoming Aspetar (Sports Medicine) Journal features a special collection of papers for those interested in neuromuscular monitoring in their programs, including a piece on rehabilitation and single-leg jumps. I highly recommend these! Also, when the NSCA releases its sports science programming, the textbook will include a chapter about using force plates, taking a more long-form and academic approach to the above concepts.
Cormack, Newton, McGuigan, et al. (2008). “Neuromuscular and endocrine responses of elite players during an elite Australian rules football season.” International Journal of Sports Physiology and Performance.
Mooney, Cormack, O’Brien, et al. (2013). “Impact of neuromuscular fatigue on match exercise intensity and performance in elite Australian football.” Journal of Strength and Conditioning Research.
Gathercole, Sporer, Stellingwerff, et al. (2015). “Alternative countermovement-jump analysis to quantify acute neuromuscular fatigue.” International Journal of Sports Physiology and Performance.
Bromley, Turner, Read, et al. (2018). “The effects of a competitive soccer match on jump performance and inter-limb asymmetries in elite academy soccer players.” The Journal of Strength and Conditioning Research.
Stone, O’Bryant, Hornsby, et al. (2019). “Using the isometric mid-thigh pull in the monitoring of weightlifters: 25+ years of experience.” UK Strength and Conditioning Association.
Constantine, Taberner, Richter, et al. (2019). “Isometric posterior chain peak force recovery response following match-play in elite youth soccer players: associations with relative posterior chain strength.” Sport (open access).
Taberner, Allen, Cohen. (2019). “Progressing rehabilitation after injury: consider the ‘control-chaos continuum.'” British Journal of Sports Medicine.
P Cormie, JM McBride, GO McCaulley. (2008). “Power-time, force-time, and velocity-time curve analysis during the jump squat: impact of load.” Journal of Applied Biomechanics.
