9/3c Biomechanics Part 2 Flashcards
what does force cause
motion
internal forces
muscle force/contraction - any force within the body
external force
produced by forces acting outside of the body
- gravity + the weight of a part of the body
- wind
- friction
- change in movement in response to external forces
musculoskeletal forces
humans are constantly producing internal forces (predominantly during muscle activation) in order to control external forces during movement tasks
active force
muscle activates
passive force
forces are generated by passive tension in stretched tissues
-someone moving your body OR doing a quad stretch
point of application
where forces are being applied in relation to the axis of rotation
center of mass
location where the gravitational forces are being applied at any limb/element of the body
angle of insertion
- orientation of the muscles insertion relative to the long axis of the bone
- when you change the angle of insertion, the total force is broken into x and y components
- at 90 degrees force is optimal
muscle moment arm
distance between the force that is acting on the body and its axis of rotation
what does muscle force do to a joint?
it creates a torque/moment about the joint allowing for rotation
linear force measure
N or lbs
angular force measure
Nm or lbft
static rotary equilibrium
internal moment = external moment:
(Muscle Force x Muscle Force Distance from joint axis of rotation) = ((mass of limb x gravity) x center of mass distance from the joint axis of rotation)
Static linear equilibrium
internal force = external force:
force generated by the muscle = reaction force pushing off of joint that muscle is acting on
in which position would a PT have to apply more force to maintain specific rotary equilibrium?
the position where the moment arm is less
Is a shorter moment arm advantageous to a patient?
Yes and no - the patient has to exert more force, but it makes it harder for the PT to then break their position
Muscle Activation
I - Isometric
C - Concentric
E - Eccentric
Isometric activation
muscle produces a force while maintaining a constant length. STATIC
Concentric activation
Muscle force overcomes the external force and muscle shortens. M(internal) > M(external)
Eccentric activation
Muscle produces a force while lengthening. Negatives at the gym, muscle resists being pulled apart - does NOT actively lengthen. M(internal) < M(external)
Can muscles have multiple actions based on the position of segments?***
YES
Does internal moment arm change when the joint position changes?***
YES - think about a rod with an axis of rotation closer to you vs farther away from you and you are the muscle force. it will be easier for you to rotate the rod when the axis of rotation is farther away from you
Conceptual framework for muscle
when a muscle contracts the free-ist segment moves
a muscle action can be produced if a moment arm/mechanical advantage is present for that plane of motion (same muscle can have multiple actions depending on the moment arm and axis of rotation)
agonist muscle
muscle or muscle group most directly related to initiation or execution of a movement
-biceps agonist for elbow flexion
antagonist muscle
muscle or muscle group that has the opposite action of the agonist muscle group
-triceps antagonist for elbow flexion
muscle synergy
muscles work together in synergy to produce a movement
force couples
forces in opposite directions produce a movement in 1 direction
-straight leg raise: force couple between your erector spinae, iliospoas, and sartorius
