Module 1-3

Question 1

what are internal mechanics?

Answer 1

mechanical factors that produce and control movement from inside the body (muscle action, ligaments)

Question 2

what are external mechanics?

Answer 2

mechanical factors affecting the body from without (gravity, brick falling on your head, car accident)

Question 3

what is an idealized force vector?

Answer 3

a single force vector representing the net effect of all force vectors to simplify computation

Question 4

what is the CoM?

Answer 4

a single point about which a body’s mass is equally distributed - not always located within the body

Question 5

what is the equation for moment of force?

Answer 5

M = d x F (moment = moment arm x force; measured in N)

Question 6

what is the moment arm?

Answer 6

the perpendicular distance from the axis of rotation to the line of force action

Question 7

what is the formula for pressure?

Answer 7

p = F/A (pressure = force / area; measured in Pa or Nm²

Question 8

what does active balancing involve?

Answer 8

keeping the CoM above and within the base of support

Question 9

what is the CoP?

Answer 9

weighted average location of all downward forces acting on the ground - location depends on foot placement and neuromuscular response to maintain balance

Question 10

what are the CoP equations?

Answer 10

CoPx = -My/Fz ; CoPy = Mx/Fz

Question 11

how many degrees of freedom are in AP & ML standing balance?

Answer 11

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

Question 12

what is the concept of four-bar linkage?

Answer 12

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

Question 13

what happens to ML standing balance as stance width increases?

Answer 13

the same hip movement produces a greater moment on the four-bar linkage; inertia decrease

Question 14

define load

Answer 14

an externally applied force

Question 15

define deformation

Answer 15

change in shape of a body when a load is applied

Question 16

define material mechanics

Answer 16

internal response of materials to externally applied loads

Question 17

define stress

Answer 17

resistance developed by tissue when externally loaded; categorized as compressive, tensile, or shear

Question 18

what is the formula for stress?

Answer 18

σ = F/A (stress = force / area; measured in Pa)

Question 19

how do we compare stress applied to different tissues?

Answer 19

normalize it by dividing the force applied over the area of the tissue; tissues with greater area will be more stiff

Question 20

define strain

Answer 20

deformation of tissue subjected to external load; also categorized as compressive, tensile, or shear

Question 21

what is the formula for strain?

Answer 21

ε = (l - l₀) / l₀ (strain = (final length - initial length) / initial length)

Question 22

how can we define stiffness?

Answer 22

the slope of the load-deformation curve; opposite of stiffness is compliance

Question 23

what is Hooke’s law?

Answer 23

stress and strain are linearly related; note that biological tissues don’t always behave linearly due to their fluid components

Question 24

what is the Hooke’s law equation?

Answer 24

σ = E x ε (stress = elastic modulus x strain)

Question 25

what is load stiffness of the human body equal to?

Answer 25

mgh; remember the small angle approximation

Question 26

what is viscoelastic tissue?

Answer 26

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

Question 27

define energy

Answer 27

the capacity for doing work

Question 28

define work

Answer 28

the energy in the process of transfer from one physical system to another

Question 29

what is potential energy?

Answer 29

the energy that a physical system stores because of its position (ex: springs)

Question 30

what is gravitational potential energy?

Answer 30

energy is stored in a physical system because of its vertical position or height in a gravity field

Question 31

what is kinetic energy?

Answer 31

the energy that a physical system possesses due to its motion

Question 32

how can energy expenditure during locomotion be measured?

Answer 32

by measuring oxygen consumption and/or production or carbon dioxide as well as heat radiation from the human body

Question 33

how we minimize energy expenditure during walking?

Answer 33

1. 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 2. some muscles are inactive during the swing phase to use less energy

Question 34

what is an example of energy dissipation in the gait cycle?

Answer 34

there is negative work done at the end of the gait cycle to prevent the leg forward

Question 35

gait cycle: what is double support?

Answer 35

when both feet are on the ground

Question 36

gait cycle: what events are in the first part of the diagram?

Answer 36

right single support, right stance phase, left swing phase

Question 37

gait cycle: what events are in the second part of the diagram?

Answer 37

left single support, right swing phase, left stance phase

Question 38

gait cycle: what is the cycle (stride) duration?

Answer 38

the time from a heel strike to the next heel strike on the same side

Question 39

define step length

Answer 39

the length from the heel of one foot to the heel placement of the other foot in the next step

Question 40

define step width

Answer 40

the perpendicular distance between foot placement of steps

Question 41

define muscle architecture

Answer 41

muscle fiber arrangement relative to the axis of force generation (angle usually varies between 0-30 at rest)

Question 42

what is physiological cross-sectional area (PCSA)?

Answer 42

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

Question 43

what is the formula for PCSA?

Answer 43

muscle mass (g) x cosθ / muscle density x fiber length

Question 44

what is muscle fiber length proportional to?

Answer 44

fiber excursion and velocity; fibers in pennate muscles is typically much shorter and have smaller excursion

Question 45

what is passive tension created by?

Answer 45

elongation of titin or connective tissue components of muscle (fascia, tendon)

Question 46

what are the components of Hill's muscle model?

Answer 46

contractile component (CE) series elastic component (SEC) parallel elastic component (PEC)