In general what should be the characteristics of an accelerometer to study postural sway?
Hello Nasser,
well this totally depends on the task (1) and the position (2) where you want to put it:
1) if we are taking about a person standing freely on a nonmoving platform 4g is easily enough, but if it is a moving platform it depends on (2).
2) You can mount the ACC on the trunk, on some joint or on the moving platform. Depending on the task you will have higher or lower accelerations and therefore also gravitational forces.
If you want an advise then I would need more information.
Kind regards. Chris
Hello Chris,
Thank you for your answer.
The person would be standing freely on a nonmoving platform executing arm movements during bipedal and unipedal conditions.
To add more prcecision, the acceleromter would be placed at the level of the L5 vertebra
Kind regards
in this case 4 g ACC is more than enough. The sample frequency does not need to be higher than 1000 Hz, I think.
Thank you Christoph. I think there is a misundertanding. My question is related to the resolution of the accelerometer i.e. the minimum detectable difference between two digitized values. In the present case it is 3.9 mg.
oh yes, now I got it! In this case I was totally misunderstanding you!
So then I need to know what you let the people do: Do the tasks require movement of the trunk (in sense of flexion in the hip joint, therefore the movements are rather slow) or are you interested in the sway you get in small movements (for example with high speed movements of the arms)?
We wish to record the postural sway when people are standing still in bipedal and unipedal postures. The movements amplitudes are small.
Are the movements expected fast? If yes then you should be fine, if not then I am afraid the resolution is to small.
You can calculate this yourself if you know the amplitudes of the movements and their time. The timing will be related to the arms movement, so I assume 4 Hz for maximum, now the amplitude of the sway would be a few centimetres. a = d^2x/dt^2.
Best of luck.
Thank you for your answer Fernando. Mainly the condition is quiet standing.
That depends on how vigorous are the "executing arm movements", Nasser Rezzoug.Try it and see what results you get. You will know what frequencies to expect by observing/filming the arm movements. Best of luck.
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