ANTHROPOMETRY - Biomechanics and Motor Control of Human Movement - page 85

Figure 4.2 Density of limb segments as a function of average body density.

4.1.3 Segment Mass and Center of Mass
The terms center of mass and center of gravity are often used interchangeably.
The more general term is center of mass, while the center of gravity refers
to the center of mass in one axis only, that defined by the direction of gravity.
In the two horizontal axes, the term center of mass must be used.
As the total body mass increases, so does the mass of each individual
segment. Therefore, it is possible to express the mass of each segment as
a percentage of the total body mass. Table 4.1 summarizes the compiled
results of several investigators. These values are utilized throughout this text
in subsequent kinetic and energy calculations. The location of the center of
mass is also given as a percentage of the segment length from either the distal
or the proximal end. In cadaver studies, it is quite simple to locate the center
of mass by simply determining the center of balance of each segment. To
calculate the center of mass in vivo, we need the profile of cross-sectional
area and length. Figure 4.3 gives a hypothetical profile where the segment
is broken into n sections, each with its mass indicated. The total mass M of
the segment is:

n

M = m i (4.3)

i = 1

where m i , is the mass of the i th section.