SEHS Topic 4.3 Continued – The Fundamentals of biomechanics – Part II

Factors affecting the location of the total body COG1. Age:

Since body segments differ in proportion to total height from birth to maturity, the transverse plane of the center of gravity will lie in a different section of the body as age increase, but the proportion of height will be constant.

The level of the COG ( Center of Gravity) will gradually decrease till it reaches the level of the second sacral vertebra at adulthood.

Cont’d Sex: • Since the distribution of body mass differ from

males to females the COG will be located higher in males than in females.

Addition to subtractions of weight in some parts of the body: Addition of weight: carrying weight will move the COG towards the location of load. E.g. carrying a weight above the head will raise it upwards. Carrying a weight behind the trunk will move the COG backwards.

COG Cont’d

Subtraction of weight, e.g. amputation of one limb will move the COG upwards and towards the sound side.

1. Body build. 2. Height.

COG Cont’d: Explain that a change in body position during sporting activities can change the position of the C.O.M./C.O.G

• The location of the center of gravity can be outside the human body during activities depending on relationship of body segments.

• The change in position of limbs from the anatomical position ( when the arrangement of the body shifts), e.g. raising both arms will raise the COG.

Additional Images – COG: Where is it?

Distinguish between first, second and third class levers

• First off…..What are levers?• Definitions – Lever: Rigid bar that turns about an axis of rotation or a

fulcrum (A) – Motive Force (F): effort or exertion applied to cause

movement against resistance or weight (a.k.a. Effort)– Resistive Force (R): opposes motive force (a.k.a. Load)

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Distinguish between first, second and third class levers Cont’d

Label anatomical representations of levers