Choosing a force plate

A FORCE PLATE IS DESIGNED TO MEASURE THE FORCES AND MOMENTS APPLIED TO ITS TOP SURFACE AS A SUBJECT STANDS, STEPS, OR JUMPS ON IT. Force plates are regularly used in research and clinical studies looking at balance, gait, and sports performance.

The diagram below shows the three force and the three moment components that are measured as a subject is in contact with the platform.

Fx, Fy, and Fz are the force components and act along the axes of an orthogonal x, y, z-coordinate system. In the diagram, the arrows point in the direction of positive force along each of the axes, following the right-hand rule. Fx and Fy are the horizontal or shear force components, and Fz is the vertical force component.

Mx, My and Mz are the three moment components. Moments are rotations around the corresponding x, y and z axes. Positive moments are determined according to the right hand rule. When looking down an axis (in its positive direction) positive moments have a clockwise rotation.

System overviews

Force plates can be used individually or arranged in a walkway format to collect multiple footfalls.

A complete force plate system consists of the force plate:Optima-HPS, Optima-BMS, or Optima-SPS, an amplifier, a computer or data acquisition system, mounting hardware, interconnecting cables, and AMTI’s data acquisition software.

To complete your system, all you need do is a connect to a PC with a Windows operating system installed.

A complete portable force plate system consists of a portable force plate (Accu-series which has a built in amplifier), interconnecting cables, and AMTI’s data acquisition software.

As with the fixed force plate system, to complete your system, all you need do is a connect to a PC with a Windows operating system installed.

Please visit our Force Plate Mounting Options and Sensing Technology and System Configuration pages for more information.

Selecting a force plate

Selecting for gait
Selecting for balance
Selecting for sports
  1. Determine whether a portable force plate is both required and appropriate for your application.

    AMTI offers three portable solutions in addition to its selection of standard force plates. These lightweight platforms are rugged, economical options designed for those whose applications require mobility and for those without the available lab space for a permanently mounted installation.

    Portable platforms may generally be left free standing and offer comparable measurement performance to mounted force plates. However, each is designed for a specific dynamic range of measurement, making them an appropriate choice when utilized for single-activity studies.

  2. Establish what size top plate will best suit the application.

    AMTI offers a wide range of platform sizes to best meet the needs of individual researcher's applications. Standard platforms sizes range from approximately 400 x 600 millimeters to 1200 x 1200 millimeters. AMTI also regularly provides custom-sized force plates for specialized applications.

  3. Decide the Fz (vertical force) capacity required by your intended use.

    Most AMTI force plates are available in 4450-, 8900-, and 17,800-Newton vertical force capacities. The capacity selected must accommodate the highest vertical load that will be applied to the platform. AMTI force plates are designed with a large safety margin, but platform damage may occur if the device is loaded beyond capacity along any of it axes. The limits of all force and moment components should therefore be examined when selecting a platform capacity.

    It should be noted that there is a tradeoff between platform capacity and platform sensitivity. Doubling the capacity halves the sensitivity and hence, the measurement resolution. It is recommended that you consult available literature on your application to determine the optimum capacity and sensitivity for your force plate.

  4. The Optima-BMS Product Line

    AMTI's Optima-BMS introduces increased levels of accuracy far beyond that of our legacy platforms, yet are currently offered at the same price. If your application requires increased accuracy, the Optima-BMS is your model line of choice.

  5. Does your application require optimal accuracy?

    AMTI's new Optima High Performance System provides levels of accuracy that were previously impossible to obtain from a force platform system. If your application requires optimal accuracy, there is no substitute.

 

Selecting a force plate for gait

Size The 400 by 600 mm and 464 by 508 mm force platforms are the standard size for gait research and will also be useful in a wide variety of other activities. These plates are ideal for gait since they allow participants to land with only one foot on the plate at a time – a requirement for inverse dynamic analysis.
Capacity Selecting the best capacity for your force plate will depend on whether you also intend to perform non-gait work in your laboratory. If your force plate is being used strictly for examining human gait and balance, a 4450-Newton capacity force plate will provide the best resolution and ample overload protection. A higher capacity force plate is recommended if you are also planning to conduct athletic performance testing.
Portable model AccuGait-O (can also be used for balance activities)
Mounted models Optima HPS, BMS400600 and BMS464508

Selecting a force plate for balance

Size Balance applications will require a force plate with a top surface area of sufficient size to accommodate the desired stance. If right-to-left comparisons are desired, two force plates will be needed. Common sizes are the 464 by 508 mm plates(HPS464508 or BMS464508), two 400 by 600 mm plates (HPS400600 or BMS400600) or one or two of the portable AccuSway-O plates. The most accurate force platforms will be the Optima-HPS, while the Optima-BMS offers a more affordable price and higher accuracy than any of our competitors.
Capacity Static balance applications are unique in that they typically generate very small forces and involve very little visible movement. Vertical loads seldom exceed body weight, and the horizontal forces are very small. In order to obtain the highest COP resolution it is best to choose the lowest capacity: 4450 Newtons (1000 lb.) and therefore the highest sensitivity, force plate available.
Portable model AccuSway-O
Mounted models Optima-HPS, BMS400600BMS400600 and BMS464508 models

Selecting a force plate for sports

Size Force plates with large top surfaces are recommended for sports applications as they provide larger target areas for capturing data during dynamic sports activities. Optima-BMS force plates provide a wide range of large platforms well-suited for sports applications. Some common sports plates are the BMS600900,BMS600600, and the BMS900900.
Capacity Sports performance applications are more demanding than normal gait and balance applications. Many sports applications, such as analysis of take-off and landing when jumping, produce large impulse forces which are potentially several times body weight. Higher capacity force plates (8900 Newton or 2000 lb.) are therefore recommended. For extremely high load activities such as Olympic weightlifting a 17,800 Newton (4000 lb.) capacity plate is also available.
Other considerations The impulse rise times in sports applications are relatively short, leading to higher-frequency content in the signal. A common guideline is that your force plate should have a natural frequency five times higher than the maximum frequency component of the signal. All Optima-BMS platforms larger than the BMS400600 use a composite top plate and are appropriate for high-frequency measurement. High-frequency versions of the smaller force plates in the Optima-HPS, and Optima-BMS series are also available.
Portable model AccuPower
Mounted models Optima HPS, Optima-BMS and Optima-BMS
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