International Society of Biomechanics
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Standards

Whole Body

M.R. (Fred) Yeadon
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December 19th,1993

Whole body orientation may be defined by successive rotations about lateral, frontal and longitudinal axes. For aerial movement the terms somersault and twist are already in use and correspond to rotations about an axis fixed in space for somersault and a longitudinal body axis for twist. In the Cardan system described, the lateral axis is considered to be initially aligned with the somersault axis. Angles may be determined from film data as described in:

Yeadon, M.R. 1990. The simulation of aerial movement - I. The determination of orientation angles from film data. Journal of Biomechanics, 23, 59-66.

There are advantages to defining the longitudinal axis in such a way that changes in body configuration have minimal effect on the body axes. This may be done as described in Appendix 2 of:

Yeadon, M.R. 1990. The simulation of aerial movement - III. The determination of the angular momentum of the human body. Journal of Biomechanics, 23, 75-83.

This choice of longitudinal axis corresponds approximately to the axis of minimum moment of inertia which is used in a theoretical analysis of whole body aerial movement in:

Yeadon, M.R. 1993. The biomechanics of twisting somersaults. Part I: Rigid body motions. Journal of Sports Sciences, 11, 187- 198.

As a consequence it is better to define the twist or longitudinal axis as the axis of minimum moment of inertia for aerial movement as in:

Yeadon, M.R. 1993. The biomechanics of twisting somersaults. Part IV: Partitioning performances using the tilt angle. Journal of Sports Sciences, 11, 187-198.

For whole body movements in other activities the minimum axis of inertia is unlikely to be as important and so the scheme of Appendix 2 may be more appropriate or even a system of axes fixed in a single segment. I would recommend that to give some consistency, a Cardan system of successive rotations about lateral, frontal and longitudinal axes be employed where these axes are defined relative to the body segments in such a way that they are mutually orthogonal. It will be necessary to have some flexibility to cater for different situations but it would be helpful if reserachers could adopt the same general system as proposed.