TYPES OF MUSCLES
Types of Muscles Tissue
There are three types of muscle tissue:
Skeletal – are those muscles
attached to bones. This muscle tissue is known as striated;
that is, the fibers or cells contain alternating light
and dark striations (bands) that are perpendicular to
the long axes of the fibers. Skeletal muscle tissue
is voluntary; that is, it can be made to contract or
relax by conscious control.
Cardiac – striated muscle forming
most of the wall of the heart. Its contraction involuntary.
Smooth- located in the walls of hollow
internal structures such as blood vessels, the stomach,
intestines, uterus and bladder. Smooth muscle fibers
are nonstriated and involuntary.
All muscles are prone to hypertrophy. Some smooth muscle
fibres, such as those in the uterus, retain their capacity
for division and can grow by hyperplasia.
Skeletal Muscles vary
in structure and function. Fibres vary in:
- colour depending on their oxygen stores [stored
in the myoglobin until needed by mitochondria].
- contraction velocity,
- their ability to split Adenosine Triphosphate (ATP).
Faster contracting fibres have greater ability to
- metabolic process they use to generate ATP.
- onset of fatigue.
Based on these structural and functional
characteristics, skeletal muscle fibres are classified
into three types: Type I fibres, Type II B fibres and
Type II A fibres.
|Twitch / Contraction Speed
|Oxygen Carrying Capacity
|ATP Split [Conversion]
||Rare in Humans
As you can probably work out – some muscles are
designed for quick bursts of intense action and others
for controlled endurance.
Any fitness program will identify the types of activities
you encounter in your normal day and work to develop
the right kinds of muscle tissue. For example: fast
twitch muscles are needed for the arms in golf and tennis;
whilst in these same sports, the legs require endurance
in both coupled with quick contraction in tennis.
Type of Muscle Loss with Age
Studies have shown that limb muscles from older men
and women are 25-35% smaller and have significantly
more fat and connective tissue than limb muscles from
Type II [fast-twitch] fibers are smaller in the old,
while the size of Type I [slow-twitch] fibers is much
Significantly smaller total number of muscle fibers
Significantly lower relative Type II fiber area, and
a significant increase in Fiber Type I area with increasing
These results indicate a gradual decrease in size/volume
with advancing age, accompanied by a replacement by
fat and connective tissue. This sarcopenia [aging atrophy]
appears to be due to a reduction in both number and
size of muscle fibers, mainly of Type II, and is to
some extent caused by a slowly progressive neurogenic