MARKER SYSTEM AND EMBEDDED AXES
The marker system described here was designed
with a minimum of markers to simplify the identification
of marker trajectories. The position of markers
(2 cm in diameter, weighing 4.4 g, developed in
this study) is shown in Fig. 2 and was selected to
satisfy the rigid body assumption as well as other
practical requirements described by Cappazzo (4).
Two markers are placed on the right and left anterior
superior iliac spines (ASIS). One other marker
is placed on a stick 10 cm long extending from the
top of the sacrum (L4-L5) and in the spinal plane. It
is stabilized by a flexible triangular plate attached to
the body with an elastic belt. Four other markers
are placed on the following locations of the particular
limb under consideration: greater trochanter,
directly lateral to the estimated average axis of rotation
of the knee joint, lateral malleolus, and space
between the second and third metatarsal heads.