Is it possible for a force plate to

[erich soemantri]

Hello all,

Our lab just got an AMTI Accupower force plate. The surface area of the force plate (101.6 x 76.3 cm) is wide enough for both foot of a subject to stand on it. So I wonder is this force plate or any force plate existed is capable of measure GRF separately, let's say in case of jumping or weight lifting, from each foot/each side of the force plate. I am sorry if this a foolish question. I am just finding out about how a force plate works myself but I am really curious though.


Cheers,


Erich

[Allan Carman]

Re: Is it possible for a force plate to

Erich

We have two AMTI AccuPower plates that are used for research and teaching. With an AMTI AccuPower plate there is a 10 pin connector that provides 8 channels of continuous analogue outputs of the 4 individual vertical forces (Fz1, Fz2,Fz3,Fz4) and 4 combined horizontal forces (Fx1-2, Fx3-4, Fy2-3,Fy1-4). I use a National Instruments A/D device and Labview to read, analyse and display these channels and with the calibration information supplied (sensitivity matrix, a, b, zo) this opens up all sorts of possibilities for sports related force and power analysis. Including counter movement, drop, squat, and broad jumps, as well as Olympic lifting to produce centre of pressure, displacement, velocity, forces, impulse, power, rate of force development as well as partitioned into phases of movement such as weighting-unweighting, 1^st and 2^nd pull.

I have found the AccuPower software limited in analysis and sample rate and is not used, so you may need to collect the analogue data and do your own analysis to get the data you want at a sufficient sample rate.

As to calculating force under each foot, it could be done indirectly. With one plate you only have one centre of pressure position but if you have a standardised foot placement, you could partition vertical force to right and left foot depending on the position of Centre of Pressure relative to the feet. I have found the horizontal forces to be poor and so have stuck to the vertical forces when using the AccuPower plate.

Cheers
Allan

[erich soemantri]

Re: Is it possible for a force plate to

Hi Allan,

Thank you very much for the extensive answer, that's unfold things to us. Yes, using the force plate with Accupower software is rather constraining.

Let me ask couple of follow through questions:
1. What kind of cable and connector that you use for the force plate-NI A/D device connection?
There is a green phoenix contact connector with a ribbon cable included in our AMTI ACP package. Do you use that for the analogue connection?

2. Is it safe to say that is not possible using only one AMTI Accupower (along with motion capture system) to calculate inverse dynamics of movements with both feet stand on the force plate (like the movements you mentioned: counter movement, drop, squat, and broad jumps and Olympic lifting) ?

Best regards,
Erich Soemantri

[Wagner De Godoy]

Re: Is it possible for a force plate to

Dear Dr. Erich Soemantri,

I have realized a project to try to measure the load in situations of double support in biomechanical force plates in 2002.
This work was done with the contribution of two companies: Motion Lab Systems ans RsScan International.

The data obtained in the project are obsolete, but may serve to aid in a new research, with better results.

You can find a copy of the project at the link below:
"Report: Division of the resulting forces in biomechanics platforms"

https://www.researchgate.net/publication/322952713_Report_Division_of_the_resulting_forces_in_biomechanics_platforms

I hope this information can be useful in your work. I apologize for the translation failures.
Best Regards,

[Allan Carman]

Re: Is it possible for a force plate to

Erich

1. What kind of cable and connector that you use for the force plate-NI A/D device connection?
There is a green phoenix contact connector with a ribbon cable included in our AMTI ACP package. Do you use that for the analogue connection?

Yes, the ribbon cable and green screw terminal can be used to connect the analogue output to your A/D device. You can also buy components and ribbon cable and make up you own break-out box.

I had a look back over the AccuPower plate specifications and found that the analogue output is filtered by a 200Hz lowpass 2nd order filter, something I had not realized. The minimum sampling frequency for a 200Hz maximum frequency of interest is 400Hz (Nyquist limit). However in practice you should sample at around 5 times the maximum frequency of interest being 1000Hz. Sampling rates beyond 1,000Hz will be of limited benefit.

2. Is it safe to say that is not possible using only one AMTI Accupower (along with motion capture system) to calculate inverse dynamics of movements with both feet standing on the force plate (like the movements you mentioned: counter movement, drop, squat, and broad jumps and Olympic lifting) ?

You could do inverse dynamics from a single plate and double support but it will involve assumption as to the forces under each foot. The issue may be finding a software packaged that is capable of doing inverse dynamics and also allow you to modify ground reaction forces and center of pressure in this way, as it is the norm to have a single foot strike per plate.

Cheers
Allan

[erich soemantri]

Re: Is it possible for a force plate to

Allan,


Thanks again for the answers.


Could you please explain briefly the inverse dynamics model that involve assumption as to the forces under each foot? Please mention the software capable of doing it.
Does the model algorithm dispart the resulting double support GRF to under each foot GRF based on body kinematics data relative to force plate?


Sincerely,


Erich

[erich soemantri]

Re: Is it possible for a force plate to

Hello Wagner,

Thank you for the response, I will read the paper first. By the way, I am still a graduate student nor a doctor : )