The document describes the segmental method for calculating the body's center of gravity. It involves dividing the body into segments, estimating the mass and center of gravity of each segment based on data from cadaver studies, then using calculations to determine the overall center of gravity location. The method takes several steps and uses tables to record segment data. It provides an estimate of the body's center of gravity but has weaknesses like being time-consuming and relying on older cadaver data.

1. Centre Of Gravity
Segmental Method

2. Lesson Objectives

Demonstrate ability to calculate Centre of mass
using the Segmental method

Identify the strengths and weaknesses.

3. Segmental method

The segmental method is the estimation of the
location of the body’s total centre of gravity

It is based on the concept that each individual
segment has its own centre of gravity

A standard set of values for mass ratio, and centre of
gravity for each body segment is used.

Cartesian coordinates are obtained for each
segment

4. Segmental method

A study on cadavers by Dempster (1955) helps us
quantify body segment parameters

Dempster collected data from 8 complete cadavers to
determine centre of rotation at each joint, segment
lengths masses and volumes.
Segment
Head
Trunk
Upper Arms
Forearms
Hands
Thighs
Shanks
Feet
Centre of Gravity Location
(% of length)
59.8% from Vertex
44.9% from supersternale
57.7% from shoulder
45.7% from elbow
79.0% from wrist
41.0% from hip
44.6% from knee
44.2% from heel
Relative Mass
(%)
6.94
43.46
5.42
3.24
1.22
28.32
8.66
2.74

5. Step 1
Make an educated guess as to
the location of the centre of
gravity
Step 2
Carefully Mark the following
segment endpoints on your drawing:
1. Vertex
2. Chin-neck Intersect
3. Suprasternal Notch
4. Shoulder axis
5. Elbow axis
6. Wrist axis
7. Knuckle
8. Hip axis
9. Knee axis
10. Ankle axis
11. Heel
12. toe

6. Step 3
Construct a stick figure, by
drawing straight lines
between appropriate end
points
Step 4
Measure the length of each
segment and record in table
1

7. Step 5
Using the lengths, and the data expressing each body CG as a
percentage of segment length, calculate the CG of each body segment.
Segment
Length (mm)
Centre of Gravity Location
(% of length)
Centre of Gravity Location
(mm)
e.g. Head length x 0.598
Head
59.8% from Vertex
Trunk
44.9% from supersternale
Upper Arm
57.7% from shoulder
Forearm
45.7% from elbow
Hand
79.0% from wrist
Thigh
41.0% from hip
Shank
44.6% from knee
Foot
44.2% from heel

8. y
Step 6
Mark the segment CG locations on
your diagram
Step 7
Plot horizontal and vertical
axis. Then for each segment,
measure the horizontal (x)
and vertical (y) distance from
each CG location to each
axis
x

9. Step 8
To find each segment moments about each axis. Multiply the relative
mass of each segment by its distance from the axis
Segment
Relative Mass
Horizontal CG Distance (X)
Horizontal Moment
Vertical CG Distance (Y)
Vertical Moment
(%)
(mm)
(mass % x X)
(mm)
(mass % x Y)
E.g. 6.94 x X
Head
6.94
Trunk
43.46
Upper Arm
5.42
Forearm
3.24
Hand
1.22
Thigh
28.32
Shank
8.66
Foot
E.g. 6.94 x Y
2.74
∑=
Centre of Mass Location X =
X=
∑=
E.G ∑ horizontal moment
100
Y=
E.G ∑ Vertical moment
100
Y=
Step 9
Calculate the X and Y co-ordinate for the TOTAL BODY CENTRE OF
GRAVITY by dividing the sum of segment moments about each axis by
the total relative body weight (100, which represents 100% of body

10. y
Step 10
Plot the Centre of gravity
location (x,y) on your
diagram
Check against your
estimated guess.
x

11. Weaknesses / Strengths.....






Data based on 8 cadavers, old ones at that. Is this data
relevant to athletes? (muscle structure)
Human error in plotting points
Time Consuming
Can be applied to actual sporting movements and
techniques
Computer software could be used to improve accuracy/
speed.
Can be fully automated using computer system to get
quantitative analysis.

12. Conclusion

Demonstrate ability to calculate Centre of mass
using the Segmental method

Identify the strengths and weaknesses.

13. Table 1
Segment
Length (mm)
Centre of Gravity Location
(% of length)
Centre of Gravity Location
(mm)
e.g. Head length x 0.598
Head
59.8% from Vertex
Trunk
44.9% from supersternale
Upper Arm
57.7% from shoulder
Forearm
45.7% from elbow
Hand
79.0% from wrist
Thigh
41.0% from hip
Shank
44.6% from knee
Foot
44.2% from heel
Table 2
Segment
Head
Trunk
Upper Arm
Forearm
Hand
Thigh
Shank
Foot
Relative Mass
(%)
Horizontal CG Distance (X)
(mm)
Horizontal Moment
(mass % x X)
E.g. 6.94 x X
Vertical CG Distance (Y)
(mm)
Vertical Moment
(mass % x Y)
E.g. 6.94 x Y
6.94
43.46
5.42
3.24
1.22
28.32
8.66
2.74
∑=
Centre of Mass Location X =
X=
∑=
E.G ∑ horizontal moment
100
Y=
Y=
E.G ∑ Vertical moment
100