Sport Books Publisher1 Chapter 3. Sport Books Publisher2 Learning Objectives To describe muscle’s...

Sport Books Publisher 1

Chapter 3


Learning Objectives

To describe muscle’s macro and micro structures

To explain the sliding-filament action of muscular

contraction

To differentiate among types of muscle fibres

To describe group action of muscles


Types of Muscle The human body is comprised of 324 muscles Muscle makes up 30-35% (in women) and 42-47% (in men) of

body mass.

Three types of muscle:

Skeletal muscle

Smooth muscle

Cardiac muscle


A. Skeletal (Striated) Muscle Connects the various parts of the skeleton through one or more

connective tissue tendons During muscle contraction, skeletal muscle shortens and moves

various parts of the skeleton Through graded activation of the muscles, the speed and smoothness

of the movement can be gradated Activated through signals carried to the muscles via nerves (voluntary

control) Repeated activation of a skeletal muscle can lead to fatigue Biomechanics: assessment of movement and the sequential pattern of

muscle activation that move body segments


B. Smooth Muscle

Located in the blood vessels, the respiratory

tract, the iris of the eye, the gastro-intestinal

tract

The contractions are slow and uniform

Functions to alter the activity of various

body parts to meet the needs of the body at

that time

Is fatigue resistant

Activation is involuntary


C. Cardiac Muscle

Has characteristics of both skeletal and

smooth muscle

Functions to provide the contractile

activity of the heart

Contractile activity can be gradated

(like skeletal muscle)

Is very fatigue resistant

Activation of cardiac muscle is

involuntary (like smooth muscle)


d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly

Components of skeletal muscle


Muscle Fibres Cylinder-shaped cells that make up skeletal muscle

Each fibre is made up of a number of myofilaments

Diameter of fibre (0.05-0.10 mm)

Length of fibre (appr. 15 cm)

Surrounded by a connective tissue sheath called Sarcolemma

Many fibres are enclosed by connective tissue sheath Perimycium to

form bundle of fibres

Each fibre contains contractile machinery and cell organelles

Activated through impulses via motor end plate

Group of fibres activated via same nerve: motor unit

Each fibre has capillaries that supply nutrients and eliminate waste


Muscle Teamwork Agonist (prime mover):

- the muscle or group of muscles producing a desired effect

Antagonist:

- the muscle or group of muscles opposing the action

Synergist: - the muscles surrounding the joint being moved

Fixators:

- the muscle or group of muscles that steady joints closer to the body axis so that the desired action can occur


Bending or straightening of elbow requires the coordinated interplay of the biceps and triceps muscles


Contractile Machinery:

Sarcomeres Contractile units Organized in series ( attached

end to end) Two types of protein

myofilaments:

- Actin: thin filament

- Myosin: thick filament Each myosin is surrounded by

six actin filaments Projecting from each myosin

are tiny contractile myosin bridges

Longitudinal section of myofibril

(a) At rest


High microscope magnification of sarcomeres within a myofibril


Contractile Machinery:Crossbridge formation and movement Cross bridge formation:

- a signal comes from the motor nerve activating the fibre - the heads of the myosin filaments temporarily attach themselves to the actin filaments

Cross bridge movement: - similar to the stroking of the oars and movement of rowing shell- movement of myosin filaments in relation to actin filaments- shortening of the sarcomere- shortening of each sarcomere is additive

b) Contraction



Contractile Machinery:Optimal Crossbridge formation

Sarcomeres should be optimal distance apart

For muscle contraction: optimal distance is (0.0019-0.0022 mm)

At this distance an optimal number of cross bridges is formed

If the sarcomeres are stretched farther apart than optimal distance:

- fewer cross bridges can form less force produced

If the sarcomeres are too close together: - cross bridges interfere with one

another as they form less force produced


c) Powerful stretching

d) Powerful contraction



Optimal muscle length and optimal joint

angle

The distance between sarcomeres is dependent on the stretch of

the muscle and the position of the joint

Maximal muscle force occurs at optimal muscle length (lo)

Maximal muscle force occurs at optimal joint angle

Optimal joint angle occurs at optimal muscle length


Muscle tension during elbow flexion at constant speed



Tendons, origin, insertion

In order for muscles to contract, they must be attached to the bones to create movement

Tendons: strong fibrous tissues at the ends of each muscle that attach muscle to bone

Origin: the end of the muscle attached to the bone that does not move

Insertion: the point of attachment of the muscle on the bone that moves


Muscle Fibre Types

Slow twitch fibres:

Slow Oxidative (Type I)

Fast twitch fibres: Fast Glycolytic (Type IIb) Fast Oxidative Glyc. (Type IIb)


A. Slow Twitch Fibres

Suited for repeated contractions during activities requiring a

force output of < 20-25% of max force output

Examples: lower power activities, endurance events


B) Fast Twitch Fibres Significantly greater force and speed generating capability than

slow twitch fibres

Well suited for activities involving high power

Examples: sprinting, jumping, throwing


The Muscle Biopsy

Used to determine muscle fibre type

1. Injection of local anesthetic into the muscle being sampled

2. Incision of approximately 5-7mm is made in the skin and fascia

of the muscle

3. The piece of tissue (250-300mg) removed via the biopsy needle

is imbedded in OCT compound

4. The sample is frozen in isopentane cooled to –180C


Muscle Biopsy


The Histochemistry

The biopsy samples are first sectioned (8-10 μm thickness) Sections are processed for myosin ATPase:

Fast twitch fibres – rich in myosin ATPase (alkaline labile)

Slow twitch fibres – low in myosin ATPase (acid labile) Sections are processed for other metabolic characteristics


Nerve-Muscle Interaction

Skeletal muscle activation is initiated through neural activation

NS can be divided into central (CNS) and peripheral (PNS)

The NS can be divided in terms of function: motor and sensory

activity

Sensory: collects info from the various sensors located

throughout the body and transmits the info to the brain

Motor: conducts signals to activate muscle contraction


Activation of motor unit and its innervation systems

1. Spinal cord 2. Cytosome 3. Spinal nerve 4. Motor nerve 5. Sensory nerve 6. Muscle with muscle fibres


Motor Unit

Motor nerves extend from the spinal cord to the muscle fibres Each fibre is activated through impulses delivered via motor end plate Motor unit: a group of fibres activated via the same nerve All muscle fibres of one particular motor unit are always of the same

fibre type Muscles needed to perform precise movements generally consist of a

large number of motor units and few muscle fibres Less precise movements are carried out by muscles composed of

fewer motor units with many fibres per unit


All-or-none Principle Whether or not a motor unit activates upon the

arrival of an impulse depends upon the so called all-or-none principle

An impulse of a certain magnitude (or strength) is required to cause the innervated fibres to contract

Every motor unit has a specific threshold that must be reached for such activation to occur


Intra-muscle Coordination

The capacity to apply motor units simultaneously is known as intra-muscle coordination

Many highly trained power athletes, such as weightlifters, wrestlers, and shot putters, are able to activate up to 85% of their available muscle fibres simultaneously (untrained: 60%)

Force deficit: the difference between assisted and voluntarily generated maximal force (trained: 10%, untrained: 20-35%)


Intra-muscle Coordination cont.

Trained athletes have not only a larger muscle mass than untrained individuals, but can also exploit a larger number of muscle fibres

Athletes are more restricted in further developing strength by improving intra-muscular coordination

Trained individuals can further increase strength only by increasing muscle diameter


Inter-muscle Coordination

The interplay between muscles that generate movement through contraction (agonists) and muscles responsible for opposing movement (antagonists) is called inter-muscle coordination

The greater the participation of muscles and muscle groups, the higher the importance of inter-muscle coordination

To benefit from strength training the individual muscle groups can be trained in relative isolation

Difficulties may occur if the athlete fails to develop all the relevant muscles in a balanced manner


Inter-muscle Coordination cont. High-level inter-muscle coordination greatly improves

strength performance and also enhances the flow, rhythm, and precision of movement

Trained athlete is able to translate strength potential to enhance inter-muscle coordination


Muscle’s Adaptation to Strength Training

Individual’s performance improvements occur through a process of biological adaptation, which is reflected in the body’s increased strength

Adaptation process proceeds at different time rates for different functional systems and physiological processes

Adaptation depends on intensity levels used in training and on athlete’s unique biological make-up

Enzymes adapt within hours, cardiovascular adaptation within 10 to 14 days

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