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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

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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 Activated through signals carried to the muscles via nerves (voluntary

control) Repeated activation of a skeletal muscle can lead to fatigue

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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

Activation is involuntary

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C. Cardiac Muscle

Has characteristics of both

skeletal and smooth muscle

Functions to provide the

contractile activity of the heart

Is very fatigue resistant

Activation of cardiac muscle is

involuntary (like smooth muscle)

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

Components of skeletal muscle

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Muscle Fibres Each fibre is made up of a number of myofilaments

Surrounded by a connective tissue sheath called

Sarcolemma

Many fibres are enclosed by connective tissue sheath

Perimycium to form bundle of fibres

Group of fibres activated via same nerve: motor unit

Each fibre has capillaries that supply nutrients and

eliminate waste

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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

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

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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

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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

Longitudinal section of myofibril

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Contractile Machinery:Optimal Crossbridge formation

Sarcomeres should be optimal distance apart

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

Longitudinal section of myofibril

c) Powerful stretching

d) Powerful contraction

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Contractile Machinery:

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

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Muscle tension during elbow flexion at constant speed

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Contractile Machinery:

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

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Muscle Fibre Types

Slow twitch fibres:

Slow Oxidative (Type I)

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

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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

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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

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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

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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

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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

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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 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

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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