BIomechanics Flashcards
biomechanics
the study of mechanical laws and principles as they relate to the human body
can be divided into statistics and dynamics
statics biomechanics
the study of bodies remaining at rest or at equilibrium as a result of the forces acting on them
dynamics biomechanics
the study of moving bodies
kinetics
the area of biomechanics concerned w/ the forces producing motion or maintaining equilibrium
kinematics
the area of biomechanics that includes descriptions of motion w/o regard for the forces producing the motion
what does kinematics allow
to visualize the motion, but no regards to how the motion occurs
force
any energy that tends to cause or change the movement of a body
gravity and muscles in biomechanics (main forces)
resistance
the body weight or external load
ex: holding out body up against gravity or 2 lb weight on the ankle
vector
a force that has magnitude, direction, line application and a point of application
ex: force vectors and resistance vectors
open kinematic chain
refer to movements that occur when the distal segment moves freely in space
- results in isolated joint movement
-distal segments –> our feet or our hands
closed kinetic chain
refers to movements that occur when the distal segment (hands, feet) is fixed and the body moves over that segment
movement at one joint results in simultaneous movements of all other joints in the kinematic chain (predictable manner)
mechanical systems in the body
3
lever system
wheel and axel system
pulley system
lever
any rigid object free to turn about a center of rotation when a force is applied
what are levers in the body
bones
force (lever system)
vector quantity
the energy that tends to cause rotation of the lever
usually muscles
denoted with a “F”
resistance (lever system)
vector quantity
the energy that tends to stop or resist rotation
usually body weight or an external load
denoted w/ a “R”
axis
the point around which the lever will rotate
joints
force arm
the perpendicular distance from the application of the force to the axis
denoted with “f”
other names of force arms
moment arm
lever arm
resistance arm
the perpendicular distance from the application of the resistance to the axis
point of application
both resistance and force vectors have a point of application
force vector point of application: muscle insertion
external load, point of application: where the object is applied
external load, weight of a body part: COG of body part
action line
indicates the pull toward the source or push away from the source
torque
the ability of a force to cause rotation of a lever
T = F x d
d=the shortest distance b/w the action line of the applied force and the axis of the lever, perpendicular tot he action line of the force and intersecting the axis
units of measure for torque
foot-pounds or inch-pounds
when is the lever at equilibrium
when the sum of all the torques are 0
first class levers
when 2 resultant forces are applied on either side of an axis, at some distance from that axis
creating rotation in opposite directions
ex: seesaw
example of first class lever in the body
triceps at the elbow
what do first class levers function to do
balance forces
relationship b/w force arm and resistance arm in first class levers
force arm may be greater than, smaller than or equal to the resistance arm
where is the axis located in a first class lever
anywhere b/w the force and resistance w/o changing the class of the lever
second class levers
whenever 2 resultant forces are applied so that the resistance lies b/w the force and the axis
relationship b/w fa and ra in second class levers
fa is always greater than ra
force arm > resistance arm
example of second class lever in the body
gastroc/soleus at the ankle when lifting the body around the axis of the toes
second class levers function to
magnify forces
will have a mechanical advantage d/t always having a larger force
you can use less force to move a given resistance
third class lever
exist whenever forces on a lever are applied so that the force lies closer to the axis of the lever than the resistance does
fa and ra relationship in third class levers
force arm is always smaller than the resistance arm
example of third class lever in the body
biceps working against gravity
most muscles that create rotation of their distal segments are third class levers
what do third class levers give us
ROM and mobility
function to increase the distance over which an object can be moved
muscle must work harder but will sacrifice that to give us ROM
2 types of wheel and axis systems
rim driven
axel driven
rim driven wheel and axis system
the force is applied at the rim
force arm is the radius of the circle
tend to magnify the force
example of rim driven
thoracic rotation by the obliques and abdominals
axel driven
the force is applied at the axel
the force arm is the radius of the axel
will tend to produce ROM, speed, distance but will sacrifice force
example of axel driven
thoracic rotation produced by small muscles of the back
there muscles have a small force arm and have to work harder but will produce a large ROM
pulley system
when the direction of a muscle pull is altered, the bone or prominence causing the deflection forms an anatomic pulley
pulley will change direction but not the magnitude of a muscle force
change results in improved ability of the muscle to generate force
in what direction is the the change of direction
away from the axis of the joint being crossed
this results in the movement arm of the muscle force is increased
muscle is able to produce more torque
example of pulley system in the body
patella is a pulley that improves the quadriceps ability to produce torque
force couple
lever system is which 2 forces of equal magnitude working at a distance from each other in opposite directions to produce rotation
what is the force coupe muscles are equal in magnitude
you will only get rotation
what if the force couple are not equal is magnitude
you will get some linear motion
example of force couple
anterior/posterior pelvic tilt
abdominals with hamstrings/glutes
types of force systems
linear
parallel
concurrent
parallel
when two or more parallel forces act on the same object at some distance from each other and at some distance from the axis around at which the lever will rotate
mechanical advantage
a measure of the efficiency of a lever
the effectiveness of the effort force as compared to resistance
Mad =
fa/ra
fa > ra then
mechanical advantage is greater than 1
small effort force can create more torque and overcome a larger resistance
tradeoff of mechanical advantage
the muscle force pulls at its point of application through a small arc so the the distal portion of the lever is moving through a greater arc
required muscle force is greater, but results in a larger ROM and increased speed of the distal segment
composition force
in a parallel force system
all forces causing rotation in one direction can be represented by a single vector acting in the same direction with a magnitude equal to the sum of the composing forces
a resultant
resolution force
the process of resolving a force into 2 or more components
taking the forces apart
what happens when a force is applied to a lver at 90 degrees
all force goes into causing movement or rotation of the lever
what happens when a force is applied at any other degrees besides 90
force applied is “Wasted” as the force isnt contributing to only rotations but some translation
rotary component
right angle to the lever
part of the force that moves the lever or is the lever is in equilibrium, part that holds it in place
translatory component
drawn parallel to the lever
portion of the force applied toward linear movement of the lever
what happens when the translatory component is towards the joint
compresses the joint for stability
what happens when the translatory component is away from the joint
distracts the joint resulting in less stability
muscle force
when the force you are resolving is a muscle force
it is always located b/w the 2 component forces
