16) Introduction to Kinesiology (Lab 5)

COM

• the point on an object or body where mass is evenly distributed in all directions (ex: balance or pivot point)

• every part of the body has its own COM

COM displacement

• displaces during all movements

• changes depending on the position you’re in

COG

• the point on the body where the force of gravity acts

• COG is interchangeable/synonyms w COM

COG goes right to COM

muscles are resisting gravity from pulling down so

• gravity

• applied contact force

external forces that act on the body

vGRF

• vertical ground reaction force that arises in response to our body contacting the ground

• pushes up against gravity

EMA

• external movement arm is the perpendicular distance between an external force and joint center (axis of rotation)

• directly proportional to mechanical advantage

mechanical advantage for the system

EMA length determines the

see saw example

• smaller weight or force produced by the child means that he has to have a certain large distance from the center to balance with the man with the greater force on the other side

• the child has the mechanical advantage

BOS

• area beneath a person or an object that makes contact with the support surface

balance

the ability to maintain the COM w/in the bounds of the base of support

mass is evenly distributed in all directions w/in a body

center of mass/gravity is the location where

COM/COG, applied

gravity acts on the _____ but other external forces can be ____ anywhere on the body

the distance between where the force is applied anywhere on the body (like us adding weights)

the EMA represents

mechanical advantage of the external force (large = large; small = small)

the length of EMA represents the

stationary support surface

BOS is the area of the body that makes contact with the

the bigger is more stable

bigger base of support vs smaller base of support

re-establish the position of COG within BOS = loss of static balance

when the COG exceeds to the BOS such that an action must occur to

by positioning/shifting our COM over our feet/BOS… brought BOS back to COM

explain how we can get out of a chair without moving trunk

• above the knee is closer to COR of hip which has a smaller EMA from knee to hip giving pt a greater mechanical advantage and more force (harder for us to break)

• at the ankle is farther away from COR increasing the EMA and giving the PT a greater mechanical advantage and the pt less force (easier for us to break)

in what position did you have to use more force to break your partner’s resistance to hold the leg up and why?

neither

what plane are you most unstable in when standing w both feet shoulder width apart

frontal

what plane are you most unstable in when standing in tandem stance

sagital

what plane are you most unstable in when standing w both feet on tip toes

frontal

what plane are you most unstable in when standing on one foot