1. Center of Gravity/Mass
Center of Gravity (CG): the point around which a body’s weight is equally balanced or distributed in all directions
Center of mass (CM): the point around which a body’s mass is equally balanced or distributed in all directions

2. Or, the point about which the sum of moments = 0

3. NOTE:
If the body is homogenous in density and symmetrical, CG lies at the center of a body
CG not necessarily within the boundaries of a body
Can the CG fall outside the human body?

6. It serves as an index of total body motion
Why is the center of gravity of interest in the study of human biomechanics?
It serves as an index of total body motion
Path of the center of gravity of a runner.
The body responds to external forces as though all mass were concentrated at the CG; this is consequently the point at which the weight vector is shown to act in a free body diagram

8. Determination of the Center of Gravity: The reaction board techniqueL
For equilibrium, moments about A = 0
F2(L) – Wrb(Lrb) – BW(d) = 0
Given: L = 198 cm
Wrb = N
BW = 712 N
F2 = 476 N
Lrb = 99 cm
d = ???
Lrb
476 (198) – 218.1(99) – 712(d) = 0
476 (198) – 218.1(99) = 712(d)
d = (476 (198) – 218.1(99) )/712 = 102 cm
If body height is 176 cm: d = (102/176) x 100 = 58% of height

9. Stability and Balance Balance – ability to control equilibrium
Stability – resistance to the disruption of equilibrium
Factors affecting stability:
Size: more mass, more inertia, more resistance to change
Relation of CG to base of support – if the line of the CG falls within the base of support, stability results
Height of CG: Higher the CG, lower the stability

10. Base of support: Area bound by the outermost regions of contact between a body and support surface(s)

11. 4. horizontally positioning the center of gravity near the edge of the base of support on the side of the external force

12. 5. Lowering the center of gravity