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Corey Scholes
06-03-2008, 10:35 AM
Hi Dalia,

In answer to your question:

"i found that some measures of the GRF are more in unloaded conditions, in comparison to loaded conditions"

There are numerous factors that might explain this finding and most of them centre around stiffness regulation of the hip, knee and ankle. Changes in walking velocity and step length can lead to alterations in joint stiffness which in turn modify the magnitude of the ground reaction forces. So if your subjects are walking at a self-selected velocity they may be speeding up/slowing down or adjusting their step length.

Alternatively, with all other factors being equal some individuals will reduce their lower limb stiffness to compensate for the increased load which shifts load absorption from the articulating surfaces of the joints to the eccentrically contracting muscles.

My apologies for the lack of references.


Corey Scholes
PhD Candidate
Institute of Health & Biomedical Innovation
Queensland University of Technology, Brisbane Australia

-----Original Message-----
From: * Biomechanics and Movement Science listserver [mailto:BIOMCH-L@NIC.SURFNET.NL] On Behalf Of dalia mosaad
Sent: Wednesday, 28 May 2008 4:17 AM
Subject: [BIOMCH-L]

I'm conducting my doctoral thesis which requires measuring the 3-D ground reaction force (GRF) (vertical-antro posterior and mediolateral forces) in children.
-I take the GRF for the children (8-11 years) with different bag style (ordinary backpack and new style ergononmic bag).

-The child walk on a 5-meter walkway with the forceplate(AMTI) at the midway(i have only one force plate).

- Firstly, the child walk without bag as a refernce value.

- Then, the child carry one of the 2 bags (random choice),each bag has 15%of the body weight, and walk along the walkway at a self selected velocity, repeating this step till making right foot landing mid-plate (3-5 trials).

- The previous step repeated with the other bag.

- The previous steps conducted to measure the GRF for the right side.

- For measuring GRF for the left side we conduct the same steps but by asking the child to walk and make the foot landing by the left side

My sample is 30 subject, after i started application on 7 children, i found that some measures of the GRF are more in unloaded conditions, in comparison to loaded conditions. I don't know is it logic? Can the acceleration be the cause in that? is there any point i must pay attention for in the following cases.
Thanks in advance for you insights.
Dalia Mosaad, PT, PhD studentAssisstant lecturer Faculty of physical therapyCairo University
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