Dear Inmaculada,

Great question! I have often wondered about this.

I think the cross leg (usually my right - I wonder if it is always the
right?) pushes the supporting tibia backwards and thereby forces the
knee into a stable posture, with the ground reaction vector well
forwards. This allows the quadriceps to be relaxed with confidence.

Two possibly related questions are:

1. Why do customers prefer bars to have a rail on which to put one foot?
2. Why do birds stand on one leg when they are asleep?

Dr. Chris Kirtley MD PhD
Associate Professor
Dept. of Biomedical Engineering
Catholic University of America
620 Michigan Ave NE, Washington, DC 20064
Tel. 202-319-6134, fax 202-319-4287

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