MUSCULAR

CONTRACTION

S

COMMON MUSCLE

FEATURES•Nervous control

•Contractibility

•Extensibility (Stretch when force is applied)

•Elasticity (Return to original size after

stretching)

•Atrophy-muscle mass decline as a result of non-

use

•Hypertrophy-muscles grow larger with training

TYPES OF MUSCULAR

CONTRACTIONSIsometric: A muscle contraction where there is no change in its

length

Isotonic: There are two types of isotonic contractions:

concentric and eccentric.

In a concentric contraction, the muscle tension rises to meet the

resistance, then remains the same as the muscle shortens.

In eccentric, the muscle lengthens due to the resistance being

greater than the force the muscle is producing.

Isokinetic:

Isokinetic contractions are similar to isotonic in that the muscle

changes length during the contraction, where they differ is that

Isokinetic contractions produce movements of a constant speed.

Generally used for rehab.

TYPES OF MUSCULAR

CONTRACTIONS

Isometric:

Isotonic:

Isokinetic:

Eccentric:

Concentric:

HOW ARE MUSCULOSKELETAL

MOVEMENTS POSSIBLE?

•The origin is where the muscle is attached to a stable

bone.

•The insertion is where the muscle attaches to the bone

which will be pulled/moved.

•What is the insertion and origin of the biceps muscle?

HOW ARE MUSCULOSKELETAL

MOVEMENTS POSSIBLE?

•For movement to occur a muscle must cross between two bones. Tendons connect muscle to bone.

•Muscles can either contract or relax.•Muscle contracts making angle smaller between the two bones.

•Muscles never work alone…–Agonist = The muscle that creates the movement. “Prime

mover”.–Antagonist = The Muscle that relaxes and allows the movement

to occur. •This is called reciprocal inhibition.

ASSISTANTS

• Fixator or stabilising muscles provide stability to the origin of

the muscle.

• Eg. trapezius stabilises shoulder during elbow flexion

• Synergist or assistant muscles assist with producing the required

movement or reduce unnecessary movement

• Eg. Brachialis and brachioradialis (elbow flexors) assist with elbow

flexion

Characteristics and

Functions of Skeletal Muscle

FibresMuscular strength is dependent

on:

1. Arrangement of muscle fibres

2. Muscle fibre type

3. Gender and age differences

4. Recruitment of muscle fibres

(Discussed later)

1. Arrangement of Muscle

Fibres

a)Fusiform

b)Penniform

i. Unipennate

ii. Bipennate

iii.Multipennate

1. Arrangement of Muscle

Fibresa) Fusiform

• The muscle fibres run the length of the muscle belly.

• Designed for mobility – low force over a long range

• Example: Sartorius and Bicep

b) Penniform

• Fibres run at angles to the tendon.

• About 75% of all skeletal muscles.

• Has three subcategories:

i. Unipennate

ii. Bipennate

iii. Multipennate

1. Arrangement of Muscle

Fibresb) Penniform

i. Unipennate

•Fibres are found on only one side of

a central tendon

•E.g. Tibialis Anterior

ii. Bipennate

•The fibres run off either side of a

central tendon

•Example: Rectus femoris

iii. Multipennate

•Fibres branch out from several

tendons.

•This arrangement enables the body

the generate the greatest force.

•Example: Deltoid

1. Arrangement of Muscle

Fibres

2. Muscle Fibre Type

Two Categories of Muscle Types:

a)Slow Twitch (Type I)

b)Fast Twitch (Type II)

• The percentage of each muscle fibre type

is genetically determined and cannot be

changed with training.

2. Muscle Fibre Type

Slow Twitch

• Type 1

• Slow breakdown ATP

• Slow contraction speed

• Red in colour.

• Resistant to fatigue

• Suitable for long distance events

2. Muscle Fibre Type

• Type 2A

–Resistant to fatigue

–Partially aerobic

–Red

–Fast breakdown ATP

–Fast contraction speed

• Type 2B

–White

–Fast breakdown ATP

–Fast contraction speed

–Fatigue easily

–Anaerobic

Characteristics of Muscle Fibre

Types

3. Gender and Age

Differences

• Muscular power is dependent on gender, size,

age and physical training.

• Higher levels of testosterone in males allows

increased muscle mass development beginning in

puberty.

• Strength peaks at ages 20-30 and then decrease

1% per year.

• Acute responses to exercise depend in the type,

intensity and duration of activity and also the

muscle fibre type recruited

–Increase motor unit and fibre recruitment

–Increase blood flow to muscles

–Increase muscle temperature

–Increased O2 supply and utilisation

–Depletion of muscle energy stores

The Muscular System and Physical

Activity