METHODS

A rapid turning movement were recorded with two cameras Photo-Sonics 16 mm at 200 frames/second.  The turning movement is a 90º degrees turning movement made as fast as possible being the right foot the supporting one.

To define the anatomical axes the anthropometrical model proposed by Vaughan et al. (1992) was used.

To observe the influence of the different JCS versus attitude vector the angles of the three joints (hip, knee and ankle) were calculated and represented. In the turning movement the time represented starts when the subject initiates the movement and finishes when the foot leaves the floor. The origin of angles (0 degrees) is considered to be the standing position.

The different JCS defined are JCS-3 (213), JCS-2 (321), JCS-1 (132), JCS+1 (123), JCS+2 (231), JCS+3 (312). Where the axis 1 is the flexo-extension axis, axis 2 is the add-abduction axis (supination-pronation in the ankle) and the axis 3 is the internal-external rotation. The numbers 213 indicate the order of axis computation following the Woltring nomenclature (Woltring 1994).

The co-ordinates of markers were calculated with the DLT and every marker was smoothed separately with general cross validation (GCV) using quintic B-splines.

JCS-1 is coincident with the system defined by Cole et al. (1993) in the ankle case.
JCS+1 is coincident with the system defined by Grood & Suntay (1983).

RESULTS

To improve the comprehension of the graphs, JCS+1, JCS+2, JCS+3 and attitude vector are represented on the left; while JCS-1, JCS-2, JCS-3 and attitude vector appear on the right.

• red attitude vector (all the graphs)
• green JCS+1 (graphs on the left) JCS-1 (graphs on the right)
• blue   JCS+2 (graphs on the left) JCS-2 (graphs on the right)
• yellow  JCS+3 (graphs on the left) JCS-3 (graphs on the right)

 
The graphs show a result similar to that obtained by Woltring in a slow walk, the vector attitude is like a mean of the different JCS.

In the turning movements studied, the angle's curves calculated with the attitude vector have a form similar to those of the curves calculated with JCS-1 and JCS+1 .

Considering the mathematical advantages of attitude vector :

•  It is less sensible to errors than JCS,
•  It has less problems of continuity (gimbal-lock effect in JCS),

The absolute value of the angles are the same describing the position of distal segment referred to proximal or proximal referred to distal.

REFERENCES

 Cole, G.K.; Nigg, B.M.; Ronsky, J.L.; Yeadon, M.R.; (1993) Application of the Joint Coordinate System to the Three-Dimensional Joint Attitude and Movement Representation: A Standardization Proposal.  Journal of Biomechanical Engineering, 115, 344-349.

Grood, E.S.; Suntay, W.J.; (1983) A Joint Coordinate System for the Clinical Description of Three-Dimensional Motions: Application to the Knee. Journal of Biomechanical Engineering. 105, 136-144.

Soutas-Little, R.W.; Beavis, G.C.; Verstraete, M.C.; Markus, T.L.; (1987) Analysis of Foot Motion During Running Using a Joint Coordinate System. Med. Sci. Sports Exerc. 19, 285-293.

Vaughan, C.L; Davis, B.L.; O?Connor, J.C.; (1992) Dynamics of human gait. Human Kinetics Books, Champaign, Illinois

Woltring, H.J.; (1994) 3-D attitude representation of human joints: a standardization proposal.
J. Biomech. 27, 1399-1414.