Kinesiology Chapter 3 & 4

Functions of a skeletal muscle?

*Continuation of pressure within body cavities *Body temperature *Control of swallowing and bowel/bladder functions *Protection to the skeleton by distributing loads and acting as shock absorbers

Types of muscle contractions?

*Isometric *Concentric *Eccentric

Functions of a skeletal muscle?

*Movement *Posture *Heat production *Joint stability *Support of visceral organs *Protection of internal tissues from injury

Muscle contraction characteristics

*No muscle can do more than shorten *Muscles only pull never push

Things to observe

--Quality of movement; speed, smoothness, rhythm, abnormal movements such as tremors

Muscle fiber

-A fiber has the ability to shorten half its length therefore a muscle with longer fibers can move a lever a greater distance than a muscle with shorter fibers

What is a motor unit

-A motor neuron plus all the muscle fibers which it innervates. -When the action potential travels down the axon it reaches all the fibers in the MU & all will normally be activated. The neuron and all its fibers act as a unit.

Endurance

-Ability to maintain a force over time or for a set number of contractions or repetitions

Gravity

-Affects all movements; it is both a stimulus and barrier to movement -Primary stimulus to muscle stretch receptors (muscle spindles) that results in muscle contractions yielding trunk and limb movements

Strength

-Amount of tension that a muscle can produce

The force output as it relates to muscle contractions

-Concentric contractions produce the least force output as compared with eccentric or isometric contractions

Characteristics of muscle tissue?

-Conductivity=ability to contract -Conductivity=ability to conduct nerve impulses -Irritability=ability to respond to stimulus -Extensibility=ability to stretch beyond normal length -Elasticity=ability to bounce back after contraction or stretching

Testing validity

-Correct positioning -Careful stabilization -Palpation of muscle -Observation of movement

Single muscle fiber

-Cylindrical elongated cell -Each fiber is surrounded by connective tissue (endomysium) -Multiple muscle fibers surrounded by (perimysium) forms muscle bundle -Groups of muscle bundles together that join into a tendon at each end are called muscles -Entire muscle surrounded by epimysium

In terms of force production

-Eccentric muscle contractions produce the greatest force followed by isometric

Criteria used to measure strength

-Evidence of muscle contraction -Amount of ROM through which joint passes -Amount of resistance against which the muscle can contract including gravity as form of resistance

What are strap muscles designed for?

-Excursion and velocity due to their long muscle fibers

Fatigue accelerated

-Fatigue will be accelerated toward the end of long or severe bouts due to the increased lactate produced by the late recruitment of fast units

Motor unit

-Fiber type of a motor unit is the same but within muscle there are MUs of different types

Types of muscle fiber Cardiac

-Forms wall of heart -Has light and dark bands like striated muscles -Contraction is myogenic -Rate of contraction may be altered by nerve impulses

What are pennate muscles designed for?

-Greater force production due to their large cross sectional areas

Functions of skeletal muscle

-Heat production Muscles use energy in order to contract, escapes as heat Muscles maintain the proper body temperature i.e. shivering to keep warm

What does the power of a muscle depend on?

-How many fibers are present

Eccentric contractions

-Internal force produced by the muscle is less than the external force or resistance producing a lengthening of the muscle

Antagonism

-It is possible for muscles to oppose or antagonize one another -Movement produced by one can always be reversed by another -Antagonism also limits and controls motions

What does range of contraction of a muscle depend on?

-Length of a muscle

MMT primary evaluation tool for patients

-Lower motor neuron disorders -Primary muscle disease -Orthopedic dysfunction

Initial stages of fatigue

-MU fail to produce force -Fast units will be recruited as brain attempts to maintain desired force by recruiting more motor units -The same force production in fatigued muscle will require greater number of MU _Additional recruitment brings in fast, fatigue-able MU

MU and Brain

-MU is the brains smallest functional unit of force developed control -The brain cannot stimulate individual fibers one at a time**MU stimulated by the brain -Action potential in motor neuron results in contraction

Firing pattern

-MU recruitment is regulated by required force -Intensity of the demand determines how many MU will be recruited **In an unfatigued muscle a sufficient number of MU will be recruited to supply desired force (Initially desired force may be accomplished with little or no involvement of fast motor units)

What is posture?

-Maintenance of a fixed body position, by keeping certain muscles in a state of sustained contraction

Muscle fiber types Fast twitch (FG)

-More powerful contractions e.g. latissimus dorsi-sprinter

Functions of skeletal muscle

-Movement Muscle actions generate tension that is then transferred to bone

Agonists

-Muscles contracting and causing movement

Antagonists

-Muscles that perform opposing actions

Synergists

-Muscles that perform the same action

How do muscles produce heat?

-Muscles use energy in order to contract. -The energy escapes as heat maintaining the proper body temperature.

MU organized into smaller units

-Muscles with increased precision movements fingers and eyes

Motor unit

-Name given to a single motor neuron ad all the fibers it activates -Average motor neuron branches out to stimulate about 600 muscle fibers

Types muscle fiber Smooth

-Non-striated -Spindle shaped -Contraction of smooth muscle is slower than striated -May contract myogenically (spontaneously) -Found on walls of visceral organs -Responsible for all internal movements -Involuntary muscle

Fatigue

-Occurs after prolonged high frequency stimuli -Occurs more readily in certain fibers**fast twitch -Muscles cannot sustain/generate expected output even as stimulus continues to be applied

Muscle fiber arrangement Fusiform

-Parallel arrangement throughout muscles (biceps, sartorius) **produce greater ROM

Muscle fiber arrangement

-Pennate-oblique, short fibers with large cross sectional arrangement **produce greater force **Unipennate (FPL)-fibers can fan out one side of tendon **Bipennate (Gastroc) -fibers fan out from central tendon **Multipennate (Deltoid)-oblique fibers converge on one tendon

Procedure for MMT

-Position -Stabilize -Palpate -Observe -Resist -Grade **Resistance not applied for P or 0 **Sometimes slight resistance applied if complete ROM in gravity eliminated plane to see if P or P+

Muscle fiber types Slow twitch (SO)

-Postural muscles good capillary supply so less build up of metabolic waste-marathoner -The soleus has > than FG fibers and is therefore more resistant to fatigue

Functions of skeletal muscle

-Posture Maintenance of a fixed body position by keeping certain muscles in a state of sustained contraction

Power

-Product of the force -Requires timing and coordination

Gravity

-Provides resistance to muscle power therefore must be considered when assigning a muscle grade ***Movements against gravity and applied resistance performed in vertical plane i.e. moving up ***Tests for weaker muscles (0, T, P, P-) usually performed in horizontal plane i.e. moving sideways

Break test

-Resistance is applied after patient has reached the end of available ROM and OT attempts to break the contraction -Resist in opposite direction of test movement

Fast twitch

-Respond rapidly but also fatigue rapidly therefore designed for mobility, non-postural

Slow twitch

-Respond slowly and are fatigue resistant therefore designed for stability and posture

Firing pattern

-Slow twitch fibers have the lowest threshold for recruitment **They are selectively utilized example walking slow/running **If suddenly an increase pace to run larger units will be recruited -As the intensity of exercise increases in any muscle, the contribution of the fast fibers will increase

Tetanus

-State of maximum contraction reached when action potentials stimulate muscles repeatedly at high frequencies (very little or no relaxation between contractions) **Can be painful (statically holding a heavy object)

Eccentric muscle contractions use

-Strengthening activities and exercise programs

Force summation

-Sustained contraction results from continuous action potentials from CNS ; muscle only partially relaxes between stimuli

Insertion

-The attachment that moves furthest on contraction

Origin

-The attachment that moves the least on contraction (often proximal)

Regulation of muscular force

-The brain combines 2 control mechanism to regulate the force a single muscle produces 1. Recruitment **Size principle-smaller MU (fewer m.fibers) have a small motor neuron and a low threshold for activation **These units are recruited 1st **As more force is demanded, progressively larger MU are recruited **Requirements for force are low but control demands are high Examples-playing piano, writing **Recruiting only a few muscle fibers gives possibility of fine control **Smaller MU are generally slow twitch fibers-marathon runners **Larger MU are composed of fast twitch fibers-sprinters **Recruitment occurs in an all or none manner

Substitution

-The brain thinks in terms of movement not of individual muscle contractions and therefore a muscle may attempt to compensate for weaker muscles that cannot perform a desired movement.

Concentric contraction

-The force produced by a muscle is greater than the external force or resistance producing a shortening of the muscle

What happens in an isometric contraction?

-The tension produced against resistance is in equilibrium and there will be no change in the external muscle length, no motion and no mechanical work

Manual muscle testing

-To measure maximal contractions of a muscle or muscle group -Determine amount of muscle power -Record gains and losses in strength -Assess how weakness is impacting performance/occupation -Prevent deformities that result from imbalances of strength -Determine need for assistive devices

Size of a MU

-Varies according to muscle function -Muscles with increase force demands and decreased fine control (quads) are organized into larger motor units

Tone

-Your readiness to contract

Isometric contraction

-internal force generated by the muscle does not exceed the external force of resistance

Interior components of a muscle cell

1. Cell membrane **Controls what enters and leaves the cell 2. Contractile proteins **Contractile machinery of muscle fibers **Organized into units called sarcomeres **Muscle length determined by how many sarcomeres line up next to each other **It is the individual myofibril, long chains of sarcomeres which produce force in muscle cells 3. Muscle spindles **Skeletal muscles contain specialized proprioceptive sense organs called muscle spindles which function to detect muscle stretch **Each muscle spindle consist of an encapsulated cluster of small striated muscle fibers. Impulses in fiber causes spindle to contract **When a muscle is stretched the sensory receptors are distorted and stimulated and relay of this information leads to muscle contraction 4. Golgi tendon organs **Located at point where muscle fibers attach to tendon **They protect tendon from stress resulting from intense periods of muscle contraction by providing an inhibitory feedback to relax muscle **Golgi tendon organs composed of collagen fibers of tendon associated with sensory nerve ending that are stimulated by excessive stretching of collagen fibers **Thus the Golgi tendon organs and muscle spindles have opposing actions and work together to integrate spinal reflex systems 5. Capillaries **Not part of muscle cell **Physically link muscle to cardiovascular system **Endurance exercise increases demand on nutrient supply and waste removal but also stimulate growth of more capillaries **Strength training decreases capillary to muscle fiber diameter ratio. Muscle fiber grows in diameter but number of capillaries remains unaltered

Types of muscle contraction

1. Concentric With bones free to move; force generated is great enough to exceed the load (shortening) 2. Eccentric With bones free to move. Force is less than load (lengthening) 3. Isometric Increase in tension without change in length; Visible muscle length does not change example yoga, carrying laundry load 4. Isotonic Muscle shortens while lifting constant load Uses specific equipment to maintain amount of load, force and speed example CPM machine 5. Tonic **Different groups of cells are kept contracted at different times **Does not produce noticeable movement **Keeps muscle tight so that it is ready to respond more quickly when movement is necessary **Responsible for maintenance of posture **Muscles with less than normal tone are flaccid **Occurs from lack of use of muscle or from damage to the motor neurons that bring impulses to it **Long duration of flaccidity=atrophy (reduction in size of muscle cells)

Regulation of muscular force

2. Rate coding **Within a given MU, there is a range of firing frequencies **Slower units operate at a lower frequency range than faster units **Force generated by a MU increases with increasing firing frequency Example refiling a cup while holding it off the table **If an action potential reaches a muscle fiber before it has completely relaxed from a previous impulse, then force summation occurs

Muscle contraction

53% of its length at the most

The only muscle operation

Contraction

Muscle test grade

Grade 5-Normal Complete full ROM against Max resistance Grade 4-Good Complete full ROM against Mod resistance Grade 3+ Complete full ROM against Min resistance Grade 3 Complete full ROM against gravity Grade 3 Complete partial ROM against gravity Grade 2+ Complete full ROM in gravity eliminated plane with resistance Grade 2 Complete full ROM in gravity eliminated plane Grade 2- Complete partial ROM in gravity eliminated plane Grade 1 Trace-only a flicker of movement Grade 0 No palpable movement

Bones

Represent about 20% body weight of a normal person

Muscle

Represents about 40% of weight of normal person

Types of muscle fibers Striated

Striated /skeletal -Among largest cells in body -Contraction is typically fast and occurs only when a cell is stimulated -Visible movements and voluntary muscle