Week 3 pt. 2: Test 1 Flashcards
what are the challenges of using movement analysis vs just a diagnosis
human movement is complex
influenced by environmental, psychologic, physiologic, and mechanical factors
solution to using movement analysis in practice
start with kinematic eval (motions) and kinetics (forces)
study these effects on body
study the musculature
what is newtons first law
law of inertia
body at rest will stay at rest unless acted on by an external torque
what is newtons second law
law of acceleration
acceleration of a body is directly proportional to the force causing it
acceleration takes place in the direction of the force
acceleration is inversely proportion to mass
F=ma
what is newtons 3rd law
for every force there is an equal and opposite reaction
what is mass
property of a physical object that quantifies the amount of matter it contains
stays the same regardless of location (i.e. not gravity dependent)
resistance that a body of matter offers to change in its position or speed upon application of force
what is inertia
directly proportional to mass
the tendancy of an object to remain unchanged
i.e. more inertia in a 7lb ball than a 5lb one; takes more force to move it
what is the center of mass
point from which its weight force acts
closely coincides with COG
in human body, COM in anatomical position lies just anterior to S2
what happens if COM is not supported
becomes unbalanced and there tends to be rotation
describe COM in a segment of the body vs the whole extremity
segment = relatively stable
whole extremity = can change when the segment relationships change
what is the difference between a force and a torque
force is required to start/stop/change linear motion
torque is required to start/stop/change rotational motion
what is static equilibrium
linear and rotational velocities are at zero
what is dynamic equilibrium
when linear and/or rotational velocities is not zero but is constant
what is mass moment of inertia (I of a body)
resistance to change a body’s angular velocity
linear counterpart to inertia
depends on the mass of the body but ALSO on the distribution of mass about the axis of rotation
describe how COM of separate limb segments can affect the mass moment of inertia
COM of separate segments do not move (i.e. thigh vs calf)
BUT depending on the movement of the limb, the distances of the COM segments can change relative to the axis of rotation (i.e. the hip)
this change can thus alter the mass moment of inertia
(for example extending the leg back would increase the mass moment of inertia compared to a neutral position because the calf/thigh are further from the hip)
would a longer or shorter limb have a greater mass moment of inertia
a longer limb
during the swing phase of running, why is there knee flexion and dorsiflexion
reduced torque needed to accelerate/decelerate
what is the equation for torque
torque = F x moment arm
unit = Newton meters (Nm)
how is torque related to mass moment of inertia
inversely proportional
Sum of T = I x a
what is momentum
quantity of motion possessed by a body
what is impulse? relevance?
force applied over a period of time
the body develops mechanisms to lessen peak external forces by prolonging the time (i.e. landing with prolonged joint motion and eccentric motion)
i.e. foot contact of gait; foot pad increases duration of loading
what is work
W = force x linear displacement
or W = torque x angular displacement
what is power
power = work / time or rate of work
positive power = work done by concentrically active muscles
negative power = work done by external load against eccentrically activated muscles
isometric = NO WORK
how does newtons 3rd law apply to the human body
foot produces a force on the ground during walking and the ground produces a ground reaction force (GRF) in the opposite direction, but in equal magnitude
describe posteriorly directed forces vs anterior directed forces in relation to GRF
posterior = i.e. initial floor contact
anterior = i.e. propulsion impulses
if they are equal, net change is 0 and momentum stays the same
what is anthropometry
measurement of features of the human body
what is the significance of joint reaction forces (JRF)
often major focus of treatment programs designed to lessen pain and prevent further joint degeneration in persons with arthritis
If you reduce the magnitude of these joint forces it allows changes in activation patterns that ultimately decrease the total weight transmitted through the joint
when does Mx (x component of biceps muscle force) create a compression vs distractive force on the elbow joint
compressive when directed towards the elbow
distractive when directed away from the elbow
what elbow position maximizes the potential for both internal and external torque
90 degrees
