Choosing a force plate
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 overviewsForce plates can be used individually or arranged in a walkway format to collect multiple footfalls.
A force plate system consists of the force plate itself:OPT, BP, or OR Series, 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, plate (Accu-series which has a built in amplifier), interconnecting cables, and AMTI’s data acquisition software.
As with the fixed fixed force plate system, to complete your system, all you need do is a connect to a PC with a Windows operating system installed..
Selecting a force plate
|Selecting for gait|
|Selecting for balance|
|Selecting for sports|
- Determine whether a portable force plate or a standard fixed force plate is most 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. Standard fixed force plates on the other hand, offer more versatility in the range of activities for which they can be used.
- 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. For gait 400x600mm plates tend to be most common, while sports applications generally use 600x600, 600x900, or larger.
- Determine the Fz (vertical force) capacity required for your intended use.
Most AMTI force plates are available in 4450, 8900, and 17,800 Newton capacities (1000, 2000, or 4000 lb.) 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. Gait and balance studies only require 1000lb capacity plates. If you would also like the option to measure jumping or other dynamic athletic movements, now or in the future, a 2000lb capacity plate would be best.
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.
- Does your application require optimal accuracy?
AMTI's new Optima Human Performance System provides unprecedented levels of accuracy that are unmatched by any other force plate on the market. If you want the most accurate data for your research, there is no substitute.
Selecting a force plate for gait
|Size||The majority of AMTI's force plates are suitable for gait. The Optima HPS, OR6, and BP400600 series represent the standard size platforms for gait research, while the BP series also provides a wider range of available sizes.|
|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 (1000 lb.) 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 now or in the future.|
|Portable model||AccuGait and AccuGait Optimized (can also be used for balance activities)|
|Mounted models||Optima HPS, BP400600 and OR6 series|
Selecting a force plate for balance
|Size||Most balance applications will only require a top surface area of sufficient size to accommodate the desired stance. When selecting a mounted force plate for balance applications, the smallest appropriate Optima HPS-, OR6- or BP-series platform will yield the highest-quality results.|
|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, AccuSway-Optimized|
|Mounted models||Optima HPS, BP400600 and OR6 series|
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. BP-series force plates provide a wide range of large platforms well-suited for sports applications. Some common sports plates are the BP600900,BP600600, and the BP900900.|
|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 BP series platforms larger than the BP400600 use a composite top plate and are appropriate for high-frequency measurement. High-frequency versions of the smaller force plates in the Optima HPS, OR6, amd BP series are also available.|
|Mounted models||Optima HPS, OPT400600, OPT400600HF, BP600600, BP600900, and BP900900|