1. KKU_Biomech_M2_L1
Center of gravity
Lesson (1)
Dr / Shimaa Essa
Lecturer of physical therapy , faculty of community,
King Khalid university

2. Upon successful completion of this lesson you would be
able to:
1- Define body center of gravity
2- Identify factors affecting location of center of gravity
3- Calculate location of center of gravity
4- Identify body’s bone and soft land marks
5- Apply steps to locate body center of gravity
6- Identify the importance of locating center of gravity

3. • Center of gravity is an imaginary balancing point where the body
weight can be assumed to be concentrated and equally
distributed. Its symbol is COG or CG.
• It is the point of exact center, around which the body may rotate freely
in all directions. It can also be called center of mass.
• Anatomically; This point can be represented by the point of intersection
of the three cardinal body planes (capital, frontal and transverse).
• The center of gravity can be located within or outside the body
depending on the body's configuration and position; it is inside an object
when the object is uniform and outside the object when it is not
uniform.

4. DEFINITIONS:
• Center of gravity is an imaginary balancing
point where the body weight can be
assumed to be concentrated and equally
distributed. Its symbol is COG or CG.
• It is the point of exact center, around which the
body may rotate freely in all directions. It can
also be called center of mass.

5. • Anatomically; This point can be represented by
the point of intersection of the three cardinal body
planes (capital, frontal and transverse).
• At this point; the summation of all forces equal
zero as well as the summation of moments equal
zero so; clockwise moment + counterclockwise
moment = zero.

6. • The center of gravity can be located within or
outside the body depending on the body's
configuration and position; it is inside an
object when the object is uniform and outside
the object when it is not uniform.

7. • It’s is located anterior to the second sacral
vertebra in the anatomical position (standing) in
normal adult person.
1) In new born: above umbilicus.
2) At six month: at the level of six thoracic vertebra.
3) At two years: at the level of umbilicus.
4) At five years: below the level of umbilicus.
5) Adult: anterior to the second sacral vertebra.

9. 1- Age: age
2- Sex: female male
3- Height: Height
4- Position of Any Segment in Relation to Total
Body Segments
5- Weight "the Weight Could be Added or
Subtracted”
(+) Weight goes to the bigger weight
(-) Weight goes to the bigger weight

10. • Total Body COG
The total body COG can be determined using
mathematical or laboratory methods.
I- Mathematical determination of COG:
a) Regarding to sex: “Croskey formula”
b) Regardless to sex: "Palmar formula"

11. Mathematical determination of COG
a) Regarding to sex: COG location can be
calculated in both male and female by “Croskey
formula”
Total body height x 55.44
In female: -------------------------------- = height of COG measured
100 from heel
Total body height x 56.18
In male: --------------------------------- = height of COG measured
100 from heel

12. Mathematical determination of COG
b) Regardless to sex: "Palmar formula"
We can calculate COG regardless to the subject sex by
multiplying 55.7 % of height and then adding 1.4 cm.
Total body height x 55.7
-------------------------------- + 1.4 = height of COG measured
100 from heel

13. - Greater trochanter.
- Anterior superior iliac spine.
- Iliac crest (L4)
- Xiphoid process.
- Spine of scapula.
- Umbilicus.
**As umbilicus may be affected by muscle
weakness or paralysis, so bony landmarks
are more accurate.

14. 1- At first, put an object over the top of the head.
2- Then, measure body height from heel to the tragus
from lateral side to avoid the disadvantage of bad
muscular distribution as belly abdomen.
3- Then, find mathematically the total body COG either
with "Palmar formula" or with "Croskey Formula".
4- Finally, find the relation of the total body COG height
to either bony landmark or soft tissue landmark.

15. 1-To maintain balance through locating
COG at its level during physical therapy
treatment.
2-To enhance patient's gait during
reeducation of walking via
pushing or grasping the patient near to
his COG.

16. 3- Total COG must be well known to identify and
determine the level of performance of athletic player.
As a result, it will help the biomechanics to improve
the players' performance.
4- Segmental COG must be known especially in
amputation. The distribution of the weight of artificial
limb must be equivalent to that of the amputated
limb.
If the weight of the artificial limb increases, the
segmental COG level will change and as a result the
total COG level will change which may place overload
on a diseased part which may cause pain.

17. Summary of
Center of gravity

18. o The center of gravity is the point of exact center, around
which the body may rotate freely in all directions. It can
also be called center of mass.
o The center of gravity is determined by two methods,
Mathematically and Laboratory.
o The mathematical method is conducted through the use
of either Croskey’s or Palmar’s formulas.
o The importance of determining body’s COG is reflected in
patient’s rehabilitation during gait training, and for
prosthetics prescription.