Biomechanics Part 2 Flashcards
What do kinetics describe?
the effect of forces on the body
Define internal forces
Forces derived from inside the body
Define external forces
Forces derived from outside the body
Define the two internal forces types
Active: activated muscles
Passive: passive tension in stretched tissues (involves give and release of tension/force)
What are external forces? examples?
wind, gravity, friction
things we adapt our movement to
Where is the point of application for musculoskeletal forces?
Where the forces are applied in the joint’s axis of rotation
these forces act on the center of mass of all external forces
What is the angle of insertion?
how the muscle’s insertion is relative to the long axis of the bone
What does a change in the angle of insertion do to the direction of force?
brings the force in multiple other directions
Define the moment arm
Distance between the force acting on the body and its axis of rotation
Joint moment is equal to
Muscle force * Moment arm
Define Static Equilibrium
Internal and external forces equal one another
Explain Joint Reaction force
the muscle wants to translate the moment, but the joint and bone opposing that movement provide force in the opposite direction
Define Static Rotary Equilibrium
Internal moment = External moment
muscle force * internal moment arm = external force * external moment arm
What creates a mechanical advantage?
A longer moment arm
What are the three types of muscle activation?
Isometric, Concentric and Eccentric
Define Isometric muscle activation
Muscle produces force while maintaining a constant length
Define Concentric muscle activation
Muscle produces a force while shortening
Internal moment > external moment
Define Eccentric muscle activation
Muscle produces a force while lengthening
External moment > internal moment
Two muscle action concepts
when a muscle contracts, the freest segment moves
a muscle action can be produced if a moment arm or mechanical advantage is present for that plane of motion
Force couple definition
Forces in opposite directions can produce a movement in one direction
In Static Linear Equilibrium, what role do the biceps muscle force, weight of the forearm, and reaction force of the humerus pushing down play?
Biceps: internal force
External force: weight of forearm
humerus: reaction force
Define muscle action
The potential for a muscle to produce osteokinematic rotation around an axis of rotation in a plane of motion
Define an agonist muscle/muscle group
m. /m. group most directly related to the initiation or execution of a movement
ex. biceps are the agonist of elbow flexion
Define an antagonist muscle/muscle group
m. /m. group that has the opposite action of the agonist m. or m. group
ex. triceps are the antagonist of elbow flexion
