Introduction to Sports Biomechanics: Analysing Human Movement ...

Table 5.1 Calculation of the two-dimensional position of the whole body centre of mass; cadaver data adjusted to correct for fluid loss
x-COORDINATE y-COORDINATE
MOMENT =
m′ym PROXIMAL DISTAL MASS
CENTRE3 ,
ym MOMENT =
m′xm MASS
CENTRE3 ,
xm DISTAL
xd PROXIMAL
xp LENGTH
RATIO1,2 lr
SEGMENT MASS
FRACTION
m′ = mi/m Head and neck 0.081 0.500
Trunk 0.497 0.450
Right upper arm 0.028 0.436
Right forearm 0.016 0.430
Right hand 0.006 0.820
Right thigh 0.101 0.433
Right calf 0.046 0.433
Right foot 0.014 0.449
Left upper arm 0.028 0.436
Left forearm 0.016 0.430
Left hand 0.006 0.506
Left thigh 0.101 0.433
Left calf 0.046 0.433
Left foot 0.014 0.449
Whole body 1.000 — — — — = Σm′xm — — — = Σm′ym Notes:
1. Using simple ratios although many biomechanists use regression equations.
2. Defined as the distance of the centre of mass from the proximal point divided by the distance from the proximal to the distal point. Joint centre locations are given in Box 6.2. The proximal point
is the proximal joint and the distal point is the distal joint except for the following. For the head and neck, the ‘proximal’ point is the top (vertex) of the head and the distal point is the midpoint of a
line joining the tip of the spinous process of the seventh cervical vertebra and the suprasternal notch (or of the line joining the two shoulder joint centres). For the trunk, the proximal point is the same
as the distal point for the head and neck and the distal point is the midpoint of the line joining the hips. For the hand, the distal point is the third metacarpophalangeal joint (the third knuckle). For
the foot, the proximal point is the most posterior point on the heel (calcaneus), and the distal point is the end of the second toe.
3. xm = xp + lr (xd −xp); ym = yp + lr (yd − yp).