View Full Version : ASI responses

Matt Taylor
03-14-2004, 08:01 PM
i originally posted this 12 days ago but didnt appear on the list - so second time lucky

my original post was with regards to the an asymmetry index (ASI) to assess gait symmetry.

The asymmetry index or symmetry index (SI), same thing, is a basic equation
used to determine symmetry

SI = (Xr-Xl)/0.5(Xr+Xl)*100

Xr = values of gait variable for right limb
Xl = value of variable for left limb.

(Herzog W, Nigg BM, Read LJ, Olsson E. Asymmetries in ground reaction force
patterns in normal human gait. Med Sci Sports Exerc 1989;21(1):110-4.)

this equation has been used mainly with regards to GRF, therefore if the
difference between F1for left and right limb was 5% then this is deemed
symmetrical. If the difference was 11% then it would be deemed asymmetrical.
I believe this 10% cut-off, everything below 10% is symmetrical, is purely
arbitrary . This method also has limitations see H. Sadeghi et al. :Gait and
Posture 12 (2000) 34-45, But if subject numbers are small then stats cant be used so it may be the
best option. The vast majority of research that has used this method has
applied it to GRF and used 10% as a cut-off. It appears not to have been
used with regards to moments or powers, therefore is the 10% cut-off point
applicable. This is what I am stuck on, if the 10% was purely arbitrary
then could another arbitrary figure be plucked out of the air for moments
and powers

thanks to those who responded (see below)

I used an index presented by
Durwood B and Rowe (1991) Symmetry - not so simple. Proceedings of the World Confederation for Physical Therapy 11th International Congress, London, United Kingdom p447-449

I think the cut-off point is pretty arbitrary and depends on the variables
that you're assessing. If you want something more objective, you can
establish the cut-off based on the range of asymmetry values observed in
healthy, control subjects.

-- George

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