Module 1-3 Flashcards
what are internal mechanics?
mechanical factors that produce and control movement from inside the body (muscle action, ligaments)
what are external mechanics?
mechanical factors affecting the body from without (gravity, brick falling on your head, car accident)
what is an idealized force vector?
a single force vector representing the net effect of all force vectors to simplify computation
what is the CoM?
a single point about which a body’s mass is equally distributed - not always located within the body
what is the equation for moment of force?
M = d x F (moment = moment arm x force; measured in N)
what is the moment arm?
the perpendicular distance from the axis of rotation to the line of force action
what is the formula for pressure?
p = F/A (pressure = force / area; measured in Pa or Nm²
what does active balancing involve?
keeping the CoM above and within the base of support
what is the CoP?
weighted average location of all downward forces acting on the ground - location depends on foot placement and neuromuscular response to maintain balance
what are the CoP equations?
CoPx = -My/Fz ; CoPy = Mx/Fz
how many degrees of freedom are in AP & ML standing balance?
AP has 1 DoF, at the ankle joint (think of it as an inverted pendulum)
ML has 5 DoF, 2 hip joints, 2 ankle joints, motion of torso relative to lower body that is influenced by changes in stance width
what is the concept of four-bar linkage?
the ankle and hip angles are mechanically coupled, as stance width increases:
a change in ankle angle leads to a larger change in hip angle, proprioceptors at the hip detect motion, CoM excursion increases
what happens to ML standing balance as stance width increases?
the same hip movement produces a greater moment on the four-bar linkage; inertia decrease
define load
an externally applied force
define deformation
change in shape of a body when a load is applied
define material mechanics
internal response of materials to externally applied loads
define stress
resistance developed by tissue when externally loaded; categorized as compressive, tensile, or shear
what is the formula for stress?
σ = F/A (stress = force / area; measured in Pa)
how do we compare stress applied to different tissues?
normalize it by dividing the force applied over the area of the tissue; tissues with greater area will be more stiff
define strain
deformation of tissue subjected to external load; also categorized as compressive, tensile, or shear
what is the formula for strain?
ε = (l - l₀) / l₀ (strain = (final length - initial length) / initial length)
how can we define stiffness?
the slope of the load-deformation curve; opposite of stiffness is compliance
what is Hooke’s law?
stress and strain are linearly related; note that biological tissues don’t always behave linearly due to their fluid components
what is the Hooke’s law equation?
σ = E x ε (stress = elastic modulus x strain)
what is load stiffness of the human body equal to?
mgh; remember the small angle approximation
what is viscoelastic tissue?
living tissue with water components, the path that the tissue follows after unloading differs from the path taken during loading; energy loss occurs during deformation
define energy
the capacity for doing work
define work
the energy in the process of transfer from one physical system to another
what is potential energy?
the energy that a physical system stores because of its position (ex: springs)
what is gravitational potential energy?
energy is stored in a physical system
because of its vertical position or height in a gravity field
what is kinetic energy?
the energy that a physical system possesses due to its motion
how can energy expenditure during locomotion be measured?
by measuring oxygen consumption and/or production or carbon dioxide as well as heat radiation from the human body
how we minimize energy expenditure during walking?
- exchange between Ek and , we simply fall forward and then step to catch ourselves, muscles only have to restore a small amount of energy that is not recovered
- some muscles are inactive during the swing phase to use less energy
what is an example of energy dissipation in the gait cycle?
there is negative work done at the end of the gait cycle to prevent the leg forward
gait cycle: what is double support?
when both feet are on the ground
gait cycle: what events are in the first part of the diagram?
right single support, right stance phase, left swing phase
gait cycle: what events are in the second part of the diagram?
left single support, right swing phase, left stance phase
gait cycle: what is the cycle (stride) duration?
the time from a heel strike to the next heel strike on the same side
define step length
the length from the heel of one foot to the heel placement of the other foot in the next step
define step width
the perpendicular distance between foot placement of steps
define muscle architecture
muscle fiber arrangement relative to the axis of force generation (angle usually varies between 0-30 at rest)
what is physiological cross-sectional area (PCSA)?
the sum of the cross-sectional areas of all fibers in a muscle (numbers of sarcomeres in parallel); directly proportional to the maximum tetanic tension generated by the muscle
what is the formula for PCSA?
muscle mass (g) x cosθ / muscle density x fiber length
what is muscle fiber length proportional to?
fiber excursion and velocity; fibers in pennate muscles is typically much shorter and have smaller excursion
what is passive tension created by?
elongation of titin or connective tissue components of muscle (fascia, tendon)
what are the components of Hill’s muscle model?
contractile component (CE)
series elastic component (SEC)
parallel elastic component (PEC)
