Learning Objectives

Question 1

what are the active contractile components of skeletal muscle

Answer 1

1. myosin heavy chain
2. actin

Question 2

what are the active regulatory components of skeletal muscle

Answer 2

1. tropomyosin
2. troponin
3. myosin light chain

Question 3

explain the steps of the sliding filament hypothesis

Answer 3

1. Ca2+ from SR attaches to troponin that causes tropomyosin to shift and expose active site on actin
2. myosin attaches to actin pulling Z discs within sarcomere closer and narrowing H band
3. binding of actin and myosin forms a cross-bridge

Question 4

the amount of force generation depends on

Answer 4

number of cross-bridges formed

Question 5

what is the ideal length of ACTIVE muscle fibers to produce largest force

Answer 5

resting length

Question 6

when considering the whole muscle, what dominants muscle force production when muscle is shortened vs. lengthened

Answer 6

shortened: active force generation

lengthened: passive tension

Question 7

what is stress

Answer 7

normalized force that is applied to a specific area

Question 8

what is strain

Answer 8

normalized change in shape that occurs in direction of applied force

Question 9

what is the stress-strain relationship

Answer 9

more force applied to an object the greater the deformation

Question 10

what is the elastic region of the stress-strain curve

Answer 10

stress applied to tissue when unloaded does not cause permanent deformation. Will return to original shape

Question 11

what is the yield point on stress-strain curve

Answer 11

point where further stress will cause permanent deformation

Question 12

what is the plastic region of the stress-strain curve

Answer 12

when stress is released from the tissue it will have some elastic recovery but also permeant deformation. Returns to NEW length

Question 13

what is residual strain

Answer 13

deformation remaining after unloading if taken beyond yield point (difference at the bottom of graph between lines)

Question 14

does the ultimate strength happen before or after the failure point in the plastic region of the stress-strain curve

Answer 14

before

Question 15

define hysteresis

Answer 15

energy lost due to H2O when the stress is removed from a tissue as it returns to its original length, it has a lower amount of stress per amount of strain

Question 16

define stress relaxation

Answer 16

when tissue is held at constant strain, overtime the stress will decrease

Question 17

define creep

Answer 17

tissue under constant stress will change in length overtime

Question 18

greatest whole muscle force of max activated muscle is at what length of muscle

Answer 18

Middle?

Question 19

PASSIVE muscle force is greatest at what muscle length

Answer 19

longest

Question 20

what structure is responsible for most of the passive force at slight to moderate stretch

Answer 20

structural proteins like titin

Question 21

what structure is responsible for most of the passive force at extensive stretching

Answer 21

extracellular CT (like tendon)

Question 22

how does viscosity influence muscle force production

Answer 22

increases resistance to motion and lowers energy return of lengthening an elastic structure

Question 23

what is force capacity with increase velocity during a concentric contraction

Answer 23

decreased force production

Question 24

what is force capacity with increase velocity during a lengthening contraction

Answer 24

increases

Question 25

why does force increase during eccentric contractions at high velocity

Answer 25

1. increased resistance leads to increased tension/force production 2. passive tension due to serial + parallel components to provide additional force 3. higher number of cross-bridge formation 4. rapid reattachment compared to shortening

Question 26

what is one reason for the decreased force production with increased velocity during concentric contractions

Answer 26

less time for cross-bridge formation

Question 27

are muscle responses to external moments usually in the same direction or different compared to the external force

Answer 27

different

Question 28

describe the internal forces that can counter a given muscle moment

Answer 28

other muscles that attach to the body segment of interest. Such as elbow flexion, the triceps also attach on the ulna and cause an extensor moment, but this is smaller than the other elbow flexors so does not prevent a net flexion moment, but does decrease it

Question 29

define net muscle moment

Answer 29

sum of all internal moments (torques) acting about given axis. only consider internal forces that DO NOT go through axis of rotation

Question 30

what is the relationship between linear and angular motion of body segments

Answer 30

linear distance traveled is equal to radius of travel arc x angular displacement (means you could increase pitch speed or club speed just by increasing length)

Question 31

define primary active muscle

Answer 31

muscle that acts directly to produce or control a desired movement at a given joint or joints

Question 32

what factors de we consider when identifying the primary muscle of an action

Answer 32

1. cross-sectional area 2. line of pull 3. length 4. moment arm

Question 33

define synergist

Answer 33

muscle(s) working cooperatively to assist the performance of another muscle

Question 34

define helping synergist

Answer 34

muscle that acts locally or peripherally to given muscle to assist in producing or controlling desire motion of joint

Question 35

define stabilizing synergist

Answer 35

muscle that acts local or peripherally to another muscle to: 1. prevent undesired motion of a joint into another plane 2. stabilize segments adjacent to moving joint

Question 36

define muscle action

Answer 36

potential for a muscle to cause movement in particular direction about given joint axis - dictated by LOA - dependent on starting position of joint

Question 37

how do we determine muscle action when we are not in anatomical position anymore?

Answer 37

1. starting position of joint 2. rotational degrees of freedom of joint 3. L.O.A 4. segment that has least resistance to motion (could be distal or proximal)

Question 38

define muscle activation

Answer 38

neuromuscular process of muscle motor unit recruitment to create muscle tension

Question 39

define mechanical work

Answer 39

force x displacement * can also be angular and use torque (moment) instead of force

Question 40

define positive work

Answer 40

force is applied in SAME direction as displacement

Question 41

define negative work

Answer 41

force applied in opposite direction as displacement

Question 42

net concentric activity is related to positive or negative work

Answer 42

positive (displacement of item is in the SAME direction as the force generated)

Question 43

net eccentric activity is related to positive or negative work

Answer 43

negative (displacement of item is in the OPPOSITE direction as the force generated)

Question 44

is work occurring during an isometric contraction

Answer 44

no

Question 45

define mechanical power

Answer 45

force x displacement / time

Question 46

what could you calculate if you knew the stair height and number of steps

Answer 46

displacement

Question 47

define mechanical energy

Answer 47

capacity to do work - either kinetic or potential energy

Question 48

what are the variables for kinetic energy

Answer 48

- mass - velocity

Question 49

what are the variables for potential energy

Answer 49

- mass - gravity - height of object

Question 50

define metabolic energy

Answer 50

energy produced through anaerobic and aerobic metabolism

Question 51

what is the difference between movement economy and movement efficiency

Answer 51

movement economy: just looks at energy used (through O2 consumption) movement efficency: looks at output/ input mechanical work accomplished for a given amount of O2 consumption

Question 52

define mechanical efficiency

Answer 52

percent of energy expended by the body that is converted to mechanical work

Question 53

define movement economy

Answer 53

metabolic energy used for given amount of submax movement

Question 54

what does an EMG signal represent

Answer 54

sarcolemmal action potentials (net change from all M.U in the recording area over a period of time)

Question 55

what is common-mode rejection

Answer 55

when using multiple recording electrodes if they record a signal at the time exact time it can be rejected and filtered out (signals from skin, etc)

Question 56

what are some clinical uses for EMG

Answer 56

1. timing of muscle activity 2. relative exertion level 3. muscle fatigue 4. biofeedback

Question 57

what do we currently use to obtain image information in labs? what information does it provide

Answer 57

used to use photos or cinematography now use videos. obtain info about position and time

Question 58

what are electrogoniometeres? pros and cons

Answer 58

obtains info about changes in voltage with movement of goni arms, but would need one for each axis of movement at joint so not used a frequently

Question 59

what are inertial measurement units used for?

Answer 59

collect acceleration data directly and used for joints or body segments

Question 60

how do we usually measure muscle activity

Answer 60

EMG