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Kinesiology > Muscle forces and levers > Flashcards

Muscle forces and levers Flashcards

1
Q

What is a motor unit

A

A motor unit is made up of a motor neuron and the skeletal muscle fibers innervated by that motor neuron’s axonal terminals

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2
Q

Summarise the sliding filament theory

A

Muscle shortens or lengthens because the tick and thin filaments slide past each other without actually changing length
Each myosin molecule is shaped like golf clubs twisted together
Cross bridges point towards the thin filament in a spiralling arrangement - these are essential for muscle contraction

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3
Q

Troponin

A

binds to calcium, releasing tropomyosin from actin allowing myosin binding

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4
Q

Changes with sarcomeres with contraction

A

decreased I band region = z bands are pulled toward the centre of each sarcomere
h zone can disappear

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5
Q

Explain the sliding filament conditions during rest

A

cross bridges lie close to myosin

binding sites on actin closed

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6
Q

Explain the sliding filament conditions during excitation

A

nerve stimulates the muscle
action potential spreads to the T tubules causing calcium ions to be release from th sarcoplasmic reticulum
It combines with troponin molecules on actin

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7
Q

Hills mechanical model of muscle

A

Contractile components. E.g actin and myosin

Elastic components - generate passive tension lengthening,

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8
Q

Length tension relationship

A

Muscle force depends on the length of the muscle - highest force generated at 100-120% resting length

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9
Q

Angle of pull

A

Angle between muscle insertion and bone on which it inserts

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10
Q

Spurt muscle

A

Insertion is closer to the joint than the origin
Muscle force mainly acts to rotate the bone
E.g biceps brachii in elbow flexion

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11
Q

Shunt muscles

A

Origin is closer to the joint than the insertion

muscle force is directed along bone

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12
Q

2 joint muscles

A

Many skills involve movement at both joints; useful to have a muscle that contributes to both
E.g spurt muscle at elbow joint, shunt muscle at shoulder

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13
Q

Can 2 joint muscles produce full wage motion at both joints simultaneously?

A

no

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14
Q

What is the rectus fomoris responsible for?

A

Hip flexion and knee extension

muscle will act on joint where it has the largest moment arm or furthest away from the joint

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15
Q

Describe the relationship between velocity of muscle contraction and cross bridge

A

As the velocity of muscle contraction increases, the cross bridge demand increases which causes fewer cross bridges to attach to and decreased force

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16
Q

Describe the force velocity relationship - eccentric actions

A

Eccentric action created = load by antagonist muscle, gravity o another external load

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17
Q

Levers in the body

A

Bones=levers

Joints= fulcrums

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18
Q

What is a fulcrum ?

A

Point around which the lever rotates

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19
Q

What is an effort arm

A

The part of the lever than the effort force is applied to

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20
Q

What is a resistance arm?

A

The part of the lever that applies the resistance force

21
Q

How do you calculate torque?

A

force x perpendicular distance from joint

22
Q

What does it mean when the resistance torque is equal to the effort torque

A

isometric movement is usually taking place

23
Q

describe the relationship between effort and effort arm and between resistance and resistance arm

A

Inverse relationship

24
Q

1st class lever

A

Fulcrum is between muscle force and the resistance
E F R
A first class lever is designed basically to produce balanced movements when the axis is midway between the force and the resistance.
E.g a seesaw
When the acid is close to the force, the lever produces speed and range of motion
When the axis is close to the resistance, the lever produces force motion
(the force is applied where the muscle inserts in the bone)

25
Q

2nd class lever

A

the resistance is between the fulcrum and the muscle force
F A E
Designed to produce force movements since a large resistance can be moved by a relatively small force

26
Q

3rd class lever

A

the force is between the fulcrum and the resistance
F E R
Designed to produce speed and range of motion movements
Most levers in the body are this type

27
Q

How do you calculate mechanical advantage?

A

Effort arm/ restate arm

28
Q

What is the mechanical advantage

A

Efficiency in about of effort needed to overcome a particular resistance

29
Q

Hill’s mechanical model of muscle

A

Representation of the muscle mechanical response

  • Contractile components e.g actin and myosin generate active tension
  • Elastic components generate passive tension
  • Parallel elastic components e.g connective tissue store elastic energy when stretched, released when muscle recoils
  • Series elastic components e.g tendons transmit tension produced by contractile component to attachment point of muscles
30
Q

What does muscle force depend on

A

The length of the muscle - highest force generated at 100 - 120% of resting length

31
Q

When is active tension reduced?

A

When muscle activated at elongated lengths (fewer cross bridges formed) and shorter lengths (filaments have exceeded ability to overlap, incomplete activation of cross bridges as fewer formed)

32
Q

What contributes to total muscle tension?

A

Contractile and elastic components

33
Q

How do tendons and other connective tissue around muscle produce a higher muscular force?

A

Resist lengthening and store elastic energy thus contribute passively

34
Q

How do muscles create movement?

A

Generates tension which is transferred via tendon to bone - creates movement

35
Q

Angle of pull

A

Angle between muscle insertion and bone on which it inserts (angle of attachment facing away from the joint)

Angle of pull decreases as the bone moves away from the anatomical position

The amount of muscular force eeed to cause joint movement is affected by the angle of pull.

36
Q

Components of muscle force

A

Stabilising/dislocating component - acts parallel to the bone, pulling it into or away from joint

Rotary component - acts perpendicular to bone

37
Q

Force velocity relationship - concentric actions

A

As shortening velocity increases, cycling rate of cross bridges increases so fewer attached at any one time so decreasing force

Velocity is increased as the expensive of a decrease in force

Max velocity with highest load

38
Q

What happens as there is an increase in velocity of muscle contraction

A

Increase cross bridge demand and so fewer cross bridges to attach to and a decrease in force

39
Q

Force velocity relationship - eccentric

A

Eccentric action created = load by antagonist muscles, gravity or another external load

Increase velocity of lengthening increases = increase force

40
Q

Mechanical advantage gained by lever

A

Lever will either give an increase in force or speed

If effort arm is less than resistance arm, less force applied to move the resistance

41
Q

Chin ups

A

Starting a chin up with the elbow in a position where the elbow flexor muscle group is approximately 90 degrees makes it easier because of the more advantageous angle of pull.

The effort arm is greater than the resistance arm so less force applied to move the resistance

42
Q

Active and passive insufficiency

A

As a muscle shortens, it’s ability to exert force diminishes. When the muscle becomes shortened to the point at which it can not generate or maintain active tension, active insufficiency is reached.

If the opposing muscle becomes stretched to the point at which it can no longer lengthen and allow movement, passive insufficiency is reached.

43
Q

Torque

A

=the turning effect of an eccentric force

The greater the distance of the force arm, the more torque produced by the force

44
Q

Eccentric force

A

a force that is applied in a direction not in line with the centre of rotation of an object with a fixed axis

45
Q

Practical application of increasing torque

A

purposely increase the force arm length in order to increase the torque so that we can more easily move a relatively large resistance

46
Q

The resistance arm

A

the distance between the axis and the point of resistance application
longer the force arm, the less force required to move the lever

47
Q

Mechanical advantage gained by lever

A

Lever with give either increase in force or speed

48
Q

What does it mean if the effort arm is greater than the resistance arm

A

Less force applied to move the resistance

49
Q

What does it mean if the effort arm is less than the resistance arm

A

Small movement moves lever with greater speed and range of motion

Kinesiology (16 decks)

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